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A History of Hindu Chemistry from the Earliest Times to the Middle of the Sixteenth Century A.D. v1.c18: The Wastage of Gold in the Course of Preparing Jewelry in Bengal

A History of Hindu Chemistry from the Earliest Times to the Middle of the Sixteenth Century A.D. v1.c18

Language
English

Contents

The Wastage of Gold in the Course of Preparing Jewelry in Bengal

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² "Indian Engineering." XIX (1896). The Mechanical Operations of Melting and Hammering have been left out.

Soldering

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The next process that we shall consider is soldering. This is undoubtedly the most important process that the goldsmith has to perform from a commercial point of view. It is in the course of this process that the practical goldsmith plays those mischievous tricks which go so hard against those who purchase his productions or order for them. The quality or quantity of solder (or *pān*) employed is the first question that is universally enquired into in all cases of commercial dealings in Indian jewelry; and while by melting some articles the value of the gold per tola is reduced by Re. 1 or 2 only, we frequently find cases in which the value is decreased at the ruinous rate of Rs. 8 or Rs. 10. This last state of affairs arises when the solder consists almost entirely of a mixture of baser metals and is at the same time fraudulently used in larger quantities than what is absolutely necessary.

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Considered, however, from the standpoint of a chemical student who investigates the subject of ascertaining the amount of metal that is lost in the operations of the goldsmith, the process of soldering is scarcely important enough to receive a separate treatment. The preparation of the solder and its reduction to the condition of small thin bits are embraced in the discussion of melting and hammering; while the loss during the blowing operation, during which the reducing flame of an oil lamp is made to play upon the solder and the parts it is meant to join together, may be supposed to have been treated during the discussion of the subject of loss of gold by volatilisation. The fact that almost all solders contain a little zinc perhaps makes the loss in their case to be much greater than in that of an alloy of gold and copper only. The following three sets of figures give the weight of gold and the weight of solder before the process of soldering and the weight of the article after the operation has been finished :—

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| Gold | Solder | Wt. of Gold & Solder after operation. |
| Tolas annas pies. | Tolas annas pies. | Tolas annas peis |
| 6 0 0 | 1 0 0 | 6 15 0 |
| 2 0 0 | 0 8 0 | 2 7 13/4 |
| 3 8 0 | 1 4 0 | 4 10 3 |

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Thus, on the whole a loss of 11 1/4 pies takes place in dealing with 14 1/4 tolas of materials. This gives the rate of loss at .79 pies per tola.

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It is proper to observe that of the loss that takes place during soldering, about one-third is due to purely physical causes, *e. g.* the loss of pieces of solder which fly off before the blowpipe. The above figures are accordingly not to be supposed as affording an accurate estimate of the amount of material that is lost by vapourisation during the operation of soldering.

Filing and Cutting

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These are the two operations of the goldsmith in the course of which gold is lost to an appreciable extent. The work of cutting is done by a class of men called *nakāshiwalās* to whom the articles are made over for the purpose. In recognition of the fact that loss of gold must inevitably take place during the operation of cutting, the goldsmith, when he takes back the articles and the particles that are chopped off the surface from the *nakāshiwalās*, generally makes an allowance of one pie per tola in favour of the latter.

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The loss which takes place during the operation of cutting as well as the loss during filing, *i.e.* rubbing the surface of gold with a steel file to make it smooth, is due to causes of a purely mechanical nature and can be prevented to a great extent by the means suggested for minimising such loss in the course of hammering and drawing.

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The operation of cutting is always, and that of filing some times, effected after the article has been coloured and polished. But as the chemical process of colouring will be treated of separately in the following pages, the mere mechanical operation of cutting and filing are here put in for the purpose of preserving continuity.

The Chemical Operations of the Goldsmith : Cleansing, Colouring and Polishing

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We now come to a process which, though not so important in the eyes of the goldsmith as some of the processes before described, is yet of the greatest consequence in the enquiry in which we are engaged. This is the process of colouring.

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If it were possible for our goldsmiths to work with pure gold, the appearance of the material would suffer very little by the various processes of heating, hammering, &c., and a mere mechanical rubbing would throw off the superficial dirt and be sufficient to expose the natural yellow surface of the unalloyed metal. This property of pure gold is due to the fact that no oxides of gold are formed at temperatures to which the metal is exposed during the operations of the goldsmith. Indeed it is well-known that gold does not unite with oxygen at any temperature.

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But the case is different with copper, the oxide of which is formed at temperatures which are ordinarily attained by the goldsmith in the course of his operations. Hence, if a mass of copper is heated in the goldsmith's fire, it is divested of its bright red colour and acquires a dirty black appearance due to the formation of a coating of cupric oxide. Now, an alloy is nothing but an intimate mechanical mixture of its constituent metals—the molecules of the several metals lying promiscuously as it were. In an alloy of gold accordingly in which copper forms a constituent part, the particles of the latter are freely interspersed between those of gold. When such a substance is heated in air, the gold particles retain their primitive yellow, but the particles of copper, which are exposed to air, are oxidised into CuO. This substance is, as we know, a black amorphous powder and it gives to the whole mass a black appearance, which becomes darker as the metal is hammered over and the powder is thoroughly spread over the surface of the metal.

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An interesting and rather curious experiment clearly illustrates the above explanation. If a piece of gold containing a little copper be heated in air and care be taken not to rub the metal in any way so as to spread the black oxide of copper over the surface, it will be found that the metal, if free from external dirt or soot, will be still yellow and tolerably bright. The yellow of the more numerous gold particles overpowers the colour of the black oxide of copper. If, however, this black substance be spread over the surface of the metal, the colour instantly changes. The spreading of the oxide is easily brought about by hammering, and thus we can take an apparently bright piece of metal and, by hammering reduce it to a jet black mass.

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The ignorant goldsmiths explain this blackening by supposing the stain of the black steel hammer to adhere to the surface of gold.

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We may, perhaps, in this connection mention a particular artifice which is sometimes employed by our goldsmiths to cleanse the surface of a gold and copper alloy, which has been blackened by fire. This method is employed whenever it is desirable in the course of working to expose the bright surface, but where it would be inconvenient, impossible or unnecessary to apply the long and laborious mode of cleansing or colouring which we shall hereafter describe, It is found that if a blackened piece of gold and copper alloy be heated in a charcoal fire to redness and then water be sprinkled on the fire, the alloy at once acquires the bright colour of gold. This phenomenon, though often practised by our goldsmiths, is a puzzle to the most intelligent among them. * * * * * The true explanation of the operation seems to be that, when placed in a charcoal fire, the cupric oxide is reduced to metallic copper. But if it is taken out when hot, it comes into contact with the air again and is oxidised. What the goldsmith does is to suddenly cool down the metal when in the reduced state and not to allow it to come into contact with the open air, until it has cooled sufficiently down, so as not to be liable to re-oxidisation.

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From what has been stated above, it will be easily seen that when a piece of golden ornament has been completed by the manufacturer, it is of a dirty dark colour and must be cleansed before it can be used. In this country mere cleansing is not sufficient, for the popular taste does not approve the new golden articles appearing and being used in the yellow colour of true gold. The articles must be "coloured" before they can be made over to the customer, by which is meant that a bright reddish colour must be imparted to them. The particular tinge which is liked by different persons is different, some people liking a colour verging very nearly on red or orange, while others have a fancy for a colour which approaches to reddish violet.

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The process of imparting the requisite shade of colour to articles of gold is one of the most cumbrous and complicated chemical operations in the whole range of indigenous arts and manufactures of India. The numerous chemical reactions that take place in the several stages of the business are of more than ordinary interest; while the immense loss of gold that apparently takes place leads one to wonder why the subject has not as yet been taken up seriously by commercial or scientific men.

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The process of colouring, so recently as 20 years ago, was universally carried out by the goldsmiths themselves, and in the villages and smaller towns the state of affairs is still the same. But in the metropolis and at the bigger stations of the province, the advantages of the principle of division of labour have lately begun to be felt in every branch of art and manufacture, and the result, so far as this particular subject is concerned, has been the springing up of a class of people whose sole business is to colour ornaments and other articles of gold. These men are known among our goldsmiths as the rungwalas. They do not charge any remuneration for their labour, but retain the fluid in which, during the process of colouring, a quantity of gold is dissolved.

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We will now follow the rungwala through the course of a complete set of processes for colouring, skipping over the mere mechanical parts of the work, but dealing a little fully with the portions which are of a chemical nature.

The Processes of the Rungwala

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The shop of a Calcutta *rungwala* is one of the most miserably furnished working-places in the whole metropolis. A charcoal fire, a pair of bellows, a few crude pieces of indigenous earthern-ware, two or three coarse pots of China, together with a few other little things, are all that greet the eager sight of the observer whom business or curiosity leads to his dark and ill-ventilated den.

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The *rungwala* has to wait till a sufficient number of golden articles are accumulated in his hands. He does not generally commence the process until he has got at least ten tolas of gold for colouring. Because the cost, the trouble and the time required, as he says, in going through a complete series of operations are such as to prohibit his doing the work with a smaller amount of gold at a time. Ordinarily a "khola", as the amount of gold coloured at one operation is called, consists of about 20 to 30 tolas of gold.

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Having got the amount of gold sufficient for working a *khola*, the first thing that the *rungwala* has to do is to cleanse the articles of all external dirt as well as the blackess due to the formation of CuO. With this view he first heats them in a charcoal fire, thus causing all the oil, charcoal dust, and other foreign substances on the surface to burn off. He next puts an earthen vessel on his fire and boils in it about a seer of the unripe fruit of tamarind (Tamarindus Indica), a sustance containing considerable amount of tartaric and other acids in the free state. Taking out these boiled articles and squeezing them so as to extract the extremely acid pulp he forms a thick syrupy fluid. In this fluid he boils the articles till the dilute acids dissolve away the cupric oxide, leaving a yellow surface of pure gold. It is found that the solution of tamarind pulp becomes distinctly blue in vitrue of the formation of copper salts.

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In the place of this rather clumsy mode of cleansing, which is largely practised even in the metropolis, some of the more adventurous rungwalas use a rather more clever and neater method. Instead of preparing a large amount of tamarind pulp, they obtain from the grocer's an ounce or two of a dull white crystalline substance which they call "acid," and a solution of this serves equally well, if not better, for their purpose. To the question as to what the substance called "acid is, they cannot give a satisfactory reply. And even the grocer who sells it cannot enlighten the inquirer more than to this extent that the article is a *gād* (scum) or a bye-product in the manufacture of some acid. Having subjected the substance to a rough chemical analysis, we came to to conclusion that the substance should be nothing more nor less than KHSO₄ or hydric potassic sulphate, an acid salt and a bye-product, as we know, in the process of manufacturing nitric acid. The reaction of this substance on the copper seems to be this:— 2 KHSO₄ + CuO = K₂SO₄ + CuSO₄ + H₂O.

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The normal salt di-potassic sulphate, copper sulphate and water are formed.

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What takes place in the gold as regards the particles of copper takes place also in the solder used as regards the particles of both zinc and copper that are on the surface.

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The oxides of copper and zinc are acted on by the dilute acids of the tamarind or the hydric potassic sulphate as the case may be, and are dissolved away in the form of soluble salts. The reaction in the latter case is:— 2 KHSO₄ + ZnO = ZnSO₄ + K₂SO₄ + H₂O.

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As the solder contains a large amount of silver, its appearance after the copper and zinc have been dissolved away, is almost perfectly white, which appears rather prominent by the side of the bright yellow surface of gold.

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The next operation of the *rungwala* is perhaps intended to carry on the operation of cleansing to a further extent. He takes about half a pound of common salt, and mixes it with an equal amount of ordinary potash alum, purchased from the bazar.

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The mixture is then reduced to the form of a fine paste. The *rungwala* now covers each of the articles to be coloured with a thin layer of this paste of salt and alum and then places them on the fire. After the paste has dried up it is washed off with water, and generally the colour of the gold appears a little bit improved. The reason of this lies in the fact that the few particles of cupric oxide that remain on the surface are not wholly dissolved out by dilute acid in the first operation are got rid of by this process.

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After having been subjected to these two processes, the article acquires almost perfectly the beautiful yellow of pure gold; but as has been stated already the *pān* or solder appears at the same time as white as pure silver. The contrast of these two different colours placed in close contiguity is rather marked; and the next operation of the *rungwala* is intended to remedy this defect. In order to make the solder and the metal appear of the same colour, he actually covers the surface of the solder with a layer of gold taken from the article itself. This is done in the course of the third process, which we will describe rather fully, as it is the most important of these stages of manipulation at which loss of gold takes place in considerable amount.

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Having placed an open earthen vessel on his fire and having put some water in it, the *rungwala* prepares a mixture consisting of about four parts of nitre (say 1 lb.), one part of common salt and 1 part of alum (say ¼ lb each).¹ He then puts the mixture into the vessel, taking care always that the water in the vessel be not more than what is necessary for dissolving about half the amount of salts added. The solution is then heated till it boils evolving large quantities of gases and fumes, amongst which chlorine can be easily detected by its unmistakable corroding odour.

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¹ Cf. p. 73 under "killing of mercury and gold," where a mixture, among other ingredients, of alum, common salt and saltpetre technically called a *vida*, is used.

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In this boiling solution the goldsmith places the cleansed ornaments so as to keep them wholly immersed. He examines them from time to time and after a while finds that a layer of shining gold has formed on the surface of the white solder. When this deposit is sufficiently thick and the whole article presents the appearance of being formed out of a homogeneous material he takes them out and, washing them well, prepares them for the next operation.

Chemical Explanation

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It is difficult to find out exactly the series of chemical reactions that take place during this period. Various impurities in the articles employed make the inquiry doubly complicated. It would, however, do for our purpose to investigate briefly the principal decompositions and formations that occur, and with this view we may suppose the reagents employed to be chemically free from foreign substances.

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It is well-known that if nitric and hydrochloric acids are brought together, certain reactions take place. If the acids be tolerably concentrated they act upon one another at ordinary temperatures, the mixture becoming yellow and giving off minute bubbles of gas, smelling like chlorine. If the acids be dilute, we have to heat the mixture to bring about the chemical change. The action that takes place consists of two of stages :—

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First, the oxygen from the nitric acid oxidizes the hydrogen of the hydrochloric acid, thus :— HNO₃ + 2HCl = H₂O + HNO₂ + Cl₂ ... (i)

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Secondly, the unstable nitrous acid that is formed acts on another molecule of HCl, producing a compound known as nitrosyl chloride and water, thus :— HNO₂ + HCl = NOCl + H₂O ... (ii)

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The reactions (i) and (ii) when expressed by a single equation may be written as follows :— NO₂OH + 3HCl = NOCl + 2H₂O + Cl₂ (iii)

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Now, here, instead of free nitric and hydrochloric acids, we have saturated solutions of a nitrate and a chloride, and an action similar to the above may take place under the influence of heat only, instead of water, the hydrates of the metals present in the nitrate and the chloride are formed. Thus, instead of equation (iii) we may have the following action :— NO₂.OK + 3NaCl + 2H₂O = NOCl + 3NaOH + KOH + Cl₂.

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When the solution boils and these actions set in, the *rungwala* puts the golden articles in it. The chlorine liberated as well as the chlorine in the nytrosyl chloride attacks the gold and reduces it to the form of a soluble chloride, which mixes with the mass of the fluid. The NO of the nitrosyl, which is liberated, is itself a colourless gas, but it rapidly unites with the oxygen of the air and forms the red fumes of nitrogen peroxide which, together with chlorine, are liberated in large quantities during the third stage of colouring.

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Now we know that if a solution of gold chloride of sufficient strength is formed and a piece of silver is dipped into it, gold is deposited on the surface of the silver, while a portion of the silver is worn away. The reaction is as follows :— AuCl₃ + 3Ag = 3AgCl + Au.

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This reaction takes place in connection with the surface of the solder which is exposed. A layer of gold is formed upon it entirely hiding the white surface, so that to all appearance the whole article seems to be composed of the same material.

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In the explanation given above, the use of alum that is added to make up the *jamak* (as the solution employed in the third stage described above is called) has not been shown, and indeed this point we have not been able to clear as satisfactorily as perhaps it is capable of.¹ It seems to undergo no chemical change, and hence does not act in the capacity of a mordant in this case, as it does so widely in the arts of dyeing or calico printing. It is also found that if no alum is added to the jamak, the coating of gold on the solder is produced, but it adheres very lightly to the surface and does not stand such processes as rubbing or brushing. Hence it seems that the only function of the alum is to fix the coating, i. e. to make it adhere firmly to the surface of the solder. Experienced goldsmiths are also of opinion that, but for the alum, the gilding of the pān would not be permanent. The way in which this is done by the alum is to a certain extent a matter of conjecture. We suppose that the action is of a mere mechanical nature. When the particles of gold stick to the surface of the solder, small quantities of alum solution remain in the pores between the separate particles. These afterwards dry up and crystallise, and the minute crystals act as a sort of mortar between the particles of gold and the surface of the solder, as well as between the particles themselves.

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¹ Mr. Chakravarti all along fails to realise the important part which alum plays in yielding sulphuric acid. Moreover in the above equation chlorine cannot be expected to be set free in presence of alkalies; see below under "the Hindu method of manufacturing calomel."

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The third process in the course of colouring is by far the most important source of loss of gold in the whole series of manipulations that the metal has to undergo. We have seen that the losses at all other stages are due to causes of a mere mechanical nature and are necessarily small. In all these cases, the gold escapes the vigilant eye of the worker and hence the extent to which it is lost sight of is minute indeed. Here for the first time the gold undergoes a chemical change—it ceases to exist as gold altogether—and is consequently lost for ever to the illiterate goldsmith.

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We should remark that only a very small part of the gold that is dissolved out in the *jamak*—as the solution of nitre, alum and salt used in the third stage described above is called—is re-deposited on the surface of the solder. A large portion of the gold remains in the solution as AuCl₃. NaCl. 2H₂O. The helpless *rungwala* can do nothing with his valuable fluid but dispose it off for a trifling sum to a class of men called *jamakwalas* who have a crude method of their own to extract some quantity of the gold from the *jamak*. We shall return to the *jamakwala* subsequently. We must now proceed to the fourth or last stage of colouring, during which the requisite colour is imparted to the metal. The articles, after being extracted from the boiling *jamak* solution, are thoroughly washed and rubbed with a brush, after which another bath is prepared for them. This consists of a solution of tamarind pulp, nitre and common salt in water, which is placed in an earthen pot on fire and heated to ebullition. A little sulphur is then added after which the articles are placed in the liquid. The sulphur is added in a finely divided state, obtained by rubbing a stick of sulphur with a little water on a piece of slate. Care is always taken to add an insufficient amount of sulphur at first, for it is found that the shade of colour that is produced in the gold depends solely on the quantity of this ingredient, which accordingly requires exceedingly carefully regulation. The *rungwala* now examines the colour from time to time, adding more sulphur gradually if he wants the colour to deepen. When the requisite shade of colour is reached, he stops adding the sulphur and keeps on boiling for some time more, after which he takes the articles off the solution and gives them a final wash and polish. If too much sulphur is added in this operation the colour becomes deep violet and finally black, and the whole process is vitiated. Under the circumstances the rungwala has to recommence the work from the very beginning.

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It may be noticed that the acid or the commercial hydric potassic sulphate is never used in this stage, as it is used in the first, instead of the tamarind pulp. The reason seems to be that as nitre is also present in the mixture, the addition of KHSO₄, in the presence of other substances, may result in the formation of nitric acid under the influence of heat.

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The chemical actions that take place during the fourth or last stage of colouring seems to be extremely difficult of explanation. There can be little doubt, however, as to the fact that the reddish violet colour is due to the deposition of a thin layer of some compound of gold on the surface of the articles. It is the determination of this compound and of the exact nature of the process by which it is formed that presents all the difficulty.

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The fact that the sulphur is one of the most essential things that are required in the production of the colour would seem strongly to suggest at the first glance that the reddish violet tint is due to the formation of one of the sulphides of gold. It appears that the subject and constitution of the compounds of gold and sulphur is one which has not yet been fully investigated by chemists. But it seems to be a well-established fact that no sulphide of gold is known which is of any other colour than black. This stands in the way of our accepting the hypothesis that the reddish violet colour of gold obtained by the Indian goldsmith is due to the formation of a layer of sulphide on the surface. From the fact that if the colouring is allowed to be overdone *i. e.* if the articles be boiled further after the required tint has been obtained, the gold acquires a deep violet colour, the same conclusion is arrived at.

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Accordingly, in spite of the fact that the amount of sulphur added regulates the whole operation of the last stage of colouring, we are constrained to search for the reddish violet colour that is developed in the formation of some other compound than a sulphide. The nature of the colour being the same as would be produced by a thin layer of a violet substance on a yellow surface, it follows that the colour of the compound formed must be violet. And the fact that when the colour is overdone, *i. e.* when a thick layer of the coloured substance is formed on the surface, the appearance of the metal is dark violet, abundantly confirms the hypothesis. The only compound of gold that possesses this characteristic colour being aurous oxide Au₂O, we are forced to the conclusion that the colour of gold is due to the formation of a thin layer of suboxide on the surface of the metal.

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An examination into the nature of the chemical actions that take place during the operation clearly shows that Au₂O is the compound formed. We have seen in investigating the chemical changes during the third stage of colouring that KNO₃ and NaCl being heated together, yield free chlorine together with KOH and NaOH. This chlorine after being liberated in the fourth stage attacks the gold and a small amount of auric chloride is formed. But at this point sulphur is added, and the nascent chlorine, instead of going to attack the gold any more, combines with the sulphur to form one or more of the sulphur chlorides. The supply of fresh chlorine being thus cut off, the heated auric chloride decomposes into aurous chloride and chlorine. The chlorine thus liberated combines with the sulphur, while the aurous chloride is acted on by the KOH and NaOH with the result that Au₂O is formed.¹ This is partly deposited on the surface of the gold producing the required colour and partly mixed with the saline solid matter present in the solution.

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¹ The explanation is scarcely satisfactory; it may be taken for what it is worth-

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The series of chemical reactions may be expressed by formula as follows:—

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(1) KNO₃ + 3NaCl + 2H₂O = NOCl + 3NaOH + KOH + Cl₂; this reaction itself consists of two stages as explained before.

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(2) 3Cl + Au = AuCl₃

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(3) 2Cl + S₂ = S₂Cl₂ (SCl₂ may also be formed in the precence of excess of nascent chlorine).

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(4) Au Cl₃ = AuCl + Cl₂

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(5) 2 AuCl + 2KOH = Au₂O + 2KCl + H₂O.

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It will be observed from the above formula that the addition of sulphur is indispensable in this operation If the excess of chlorine were not removed by sulphur, as is done in (3) above, the gold would continue to be dissolved out and a large loss of the metal would arise as in the course of the third stage.

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Moreover, with a free supply of chlorine, the auric chloride would never be reduced to aurous chloride, and thus no formation of aurous oxide could take place. It is thus seen that, though the sulphur used is not directly contained in the compound which gives the colour, it regulates the whole reaction in the most important stages of its progress.

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The above hypothesis is supported by the fact that if a little sulphur is added to the fluid obtained in the fourth stage of colouring, it will be found to disslove in the fluid. This could not be the case unless a compound like S₂Cl₂, which can hold sulphur in solution, were formed during the re-action.

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It has been mentioned above that the loss during the third operation of colouring is considerable. Indeed, from the records of observation given at the end of this section, it is clear that the loss is not only large, but that its extent is also uncertain in the extreme. In some cases it is as low as half a pie per tola, while in others it reaches the ruinous figure of six pies per tola, or nearly one tenth of the whole weight. The average amount of 2½ pies per tola, which is obtained from our figures, is not very different from the idea of experienced *rungwalas* and goldsmiths on the subject. The largeness and uncertainty of loss are easily accounted for by the ever-varying constitution of the bazar articles used in the operation, some of them being very nearly pure, while others contain as much as 25 to 30 per cent of impurities, as well as by the want of any accurate precision as regards the proportion of materials employed. The ingredients are seldom weighed before being mixed together; and the varying amount of water present physically in the salts is an additional source of error and confusion in settling the proportion by mere inspection of bulk.

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The following figures will give some idea as to the magnitude of the loss in colouring:—

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| Weight before colouring. | | | Weight after colouring. | | | Loss. |
| Tolas. | Annas. | Pies. | Tolas. | Annas. | Pies. | Pies. |
| 6 | 10 | 0 | 6 | 7 | 1.5 | 10.5 |
| 3 | 2 | 0 | 2 | 14 | 1 | 15 |
| 12 | 12 | 1 | 12 | 5 | 3 | 26 |
| 5 | 3 | 2 | 5 | 2 | 0 | 6 |
| 3 | 0 | 2 | 2 | 12 | 0 | 18 |

The Restorative Processes

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Having in the previous paragraphs described with tolerable fulness the various sources of loss of gold in the course of its artistic manipulation by the Indian goldsmith and having in each case pointed out the form in which the metal escapes the hold of the worker, we will now turn our eyes to the methods which now obtain in our country for recovering, as far as possible, the amount of material which is lost. It is perhaps worth while here to point out that to re-obtain the entire amount of lost material is absolutely impossible from the innate property of the extreme divisibility of matter; and our sole object in these restorative operations should be to secure the recovering of the largest amount of metal that can possibly be saved. There are two small classes of men in Bengal who obtain their living by extracting gold from the refuse and bye-products of the goldsmith's workshop. These are the *neharwala* and the *jamakwala* before alluded to. These classes of men are found to cluster in the suburbs of large towns and important centres of jewelry manufactures. In the smaller towns and more insignificant villages, the bye-products have either to be thrown away or to be disposed of in the best manner that the goldsmith can hit upon. Not unfrequently in such cases the goldsmith himself undertakes to play the part of a *jamakwala* and *neharwala* to the best of his abilities. But the unpractised manipulation of processes, which are themselves far from being satisfactory is sure to result always in the loss of a large portion of gold.

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We will now proceed to describe the operations of the *neharwala* and the *jamakwala*. It may, however, be marked here that the immense difficulty in the way of obtaining the slightest information regarding the indigenous methods adopted by these workmen, in the exercise of their profession, can hardly be appreciated by one who has not personally made an attempt to penetrate into the mysteries of any of the trade or manufacturing secrets of India. The unfortunate stagnation of almost all departments of knowledge, art and industry in India that perplexes and mortifies an inquirer, owes its origin to a longstanding and universal spirit of conservatism inherent in our people which, however eloquently defended by orthodox advocates of caste, is manifestly one of the principal causes why the Indian craftsman lags so far behind in the modern race of nations. The healthy broadness of views, resulting from the dissemination of liberal English ideas among the masses, has, indeed, broken some of the most pernicious strongholds of the intellectual monopolies of India; but there are classes of men who still in obscure nooks of society keep to themselves what they regard as the treasures of professional secrets but what, after all, may be mere child's play to the eyes of the scientific world.

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To our enquiries about the nature of the *neharwala* and the *jamakwala* the deafest ears were turned. Our attempts to impress upon these people the necessity of the application of chemistry to improve their methods were mere cries in the wilderness. And it was not until we had spent several weeks in constant intercourse with these people that we could begin to collect the information necessary for such an inquiry. Bit by bit we gained from different sources some knowledge of the processes which are given below in a continuous and well-arranged form.

The Neharwala

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Now and then the *neharwala* makes his appearance in the goldsmith's workshop, in order to obtain the collected sweepings and other refuse of the rooms, The interval of time varies from one to three months according to the nature of the work that carried on in the rooms as well as to the amount of gold that is manufactured into ornaments. It is useful to state here that every day before work is commenced, the room is swept very clean and the sweepings, instead of being thrown away, are carefully stored up in a corner.

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The heap of dust and rubbish thus accumulated from day to day is the chief object of the visit of the *neharwala*. Having inquired as to the amount of gold that has undergone manipulation since the last disposal of sweepings or *nehar* (from this the *neharwala* gets his name) as well as the nature of the articles that were manufactured, he proceeds to settle the price which depends chiefly on these conditions. The *nehar* of twenty tolas of good gold manufactured into articles, which required drawing, beating as well as soldering would generally be disposed of for a single rupee. It may be interesting to observe that a goldsmith, however dishonest in other respects, would never deceive a *neharwala* by selling to him a heap of ordinary rubbish for fear of losing credit and custom in the department of *nehar*-selling.

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The next thing that the *neharwala* wants to obtain is the heap of rejected crucibles.

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It has been stated before that indigenous crucibles cannot be employed more than once for melting purposes, and hence the number of waste crucibles is not small in our goldsmith's workshop. The nature of the crucibles and the amount of metal melted in each, together with the qualities of the gold, settle the price. We have seen a score of crucibles of average size selling for eight annas.

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If the goldsmith’s shop is large, the soot hanging from the ceiling and walls is also purchased.

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The last thing that the *neharwala* asks the shopkeeper is whether that day he would give a *taljhar*, by which is meant if he would allow the workmen’s mats to be removed and shaken and the space below the mats swept. This operation is ordinarily perfomed once a year. The sweepings thus obtained are again valued. And after paying the prices the *neharwala* returns home with his heavy load, which sometimes reaches the respectable weight of 50 or 60 pounds.

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The first thing that the *neharwala* does with his materials is to crush them fine. This is only necessary when earthen lumps of large size are formed and mixed up with the *nehar* in considerable numbers and is dispensed with in most cases where the large pieces are few in number and can be picked up and thrown away.

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The second process is to throw the curshed materials into a big earthen pot in which the *nehar* remains immersed in water for a certain number of days, depending on the quality and quantity of the *nehar*. The object of this is to reduce fragments of clay to a fine state of division by which particles of gold that might otherwise remain imbedded inside the mass of earthy lumps are at once exposed to view.

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The next and the main operation is that of working. The thoroughly soaked *nehar* is put in large earthen vessels and more water is added if necessary. The mass is then thoroughly stirred and the lighter earthy material which yet floats when the heavy metallic matter has settled in the bottom, is taken off. By the repetition of this process the solid matter is reduced to a very small bulk. It is then allowed to settle and the water is slowly poured off. The moisture that yet remains is dried up either on fire or in the sun.

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When several *nehars* have been separately washed in the preceding way, the remnants of all the washings are mixed together and the mixture in washed once again. This operation is exactly like the preceding but is carried on more carefully and in better vessels. When it has been completed, about one-quarter of the mixture may be perceived to consist of metallic substances.

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Among the metals present in this mixture, iron is often found and, as its presence is extremely undesirable when the meterials are placed on the crucible for melting, it is generally got rid of at this stage. Formerly this was done by picking up the separate bits of iron by fine pincers, but now-a-days the magnet is almost universally used for the purpose.

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The next process is that of melting. This is carried on in the ordinary way, care being taken to procure a crucible big enough for the purpose. The earthy matter sticks to the sides of the crucible, while the metallic portion melts and falls to the bottom. A mixture of gold, silver, copper and zinc is thus obtained.

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The old method of obtaining pure gold from such a mixture as this is said to have been as curious and interesting as certainly it was laborious and protracted. The alloy was first of all beaten into leaves of extreme thinness, about 5 inches square in size. Each leaf was then covered with a thin layer of a paste of brick dust and common salt. The leaves were finally arranged one above another and exposed to the heat of fire. After a certain number of days, depending on the nature of the alloy and the temperature of the fire, the gold was found to be very nearly pure.

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This method has now, however, been entirely superseded by the far easier and more economical process of treating the alloy with strong nitric acid.

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For this purpose, however, the metal must be obtained in a fine state of division. This is done rather ingeniously by melting the material and, while molten, by suddenly dropping it in water. By this means the metal is at once reduced to a fine powder without the expenditure of any manual labour in the way of hammering. Care, however, should always be taken to see that the vessel of water in which the molten metal is dropped has a wide mouth. On one occasion, at which we were present, the liquid metal was poured into a narrow-mouthed vessel, and the steam suddenly generated was so great and powerful as to very nearly cause an explosion.

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The extraction of gold from rejected crucibles is done much in the same fashion. These are pulverised and treated in the same way as ordinary *nehar*. Sometimes the powders of crucibles are mixed up with the common *nehar* to avoid the necessity of a separate series of operations, but more frequently the smallness of their bulk induces the *neharwala* to treat them separately.

The Jamakwala

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We will now turn our attention to the methods of the *jamakwala*. He periodically visits the workshops of his patron, the *rungwala* from whom he obtains the necessary amount of *jamak* on the payment of a price which depends on the quality and the quantity of gold that has been coloured, as well as the loss of weight that has taken place in the articles during their make. To give an approximate idea of the commercial value of *jamak* it may suffice to state that we once purchased a *jamak* of 20 tolas of sovereign gold (which is 22 carats or 916.66 per mille fine) for one rupee only. We may also observe that the demand of *jamak* is not at present at par with the amount of its supply; and at some of the bigger *rungwala's* working-rooms, one may see big earthen jars full of this substance, collected and stored up for want of purchasers. It may be interesting to add that even in this obscure department of business, the evil genius of man has set to work, and one has to be careful in dealing with a *jamakwala*, if one is a new hand in these affairs.¹ On one occasion we happened to be defrauded and were given a substance as a *jamak* of 35 tolas of gold for what we considered the modest price of Rs. 2. But the thing turned out to be an imitation *jamak* only and all our best efforts could not discover in it the slightest trace of gold.

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¹ It may be observed, however, that a *rungwala* would never deceive a *jamakwala* in the same way as he would deceive a stranger for fear of losing credit and custom in the department of *jamak*-selling.

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Having obtained a sufficient amount of this fluid the *jamakwala* returns home. His first step is to get rid of the fluid part of the *jamak* by boiling it. For this purpose he has got large earthen vessels with wide mouths which can be placed over a fire. When almost the whole amount of water has been evaporated off, he pours out the viscous mass into an open eathern vessel and porceeds to what we shall call the second process of the *jamakwala*.

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With the solid matter of the *jamak* obtained by the first operation, the *jamakwala* mixes a small quantity of borax as well as a large amount of a substance known as *poonoor*. The weight of powdered *poonoor* that is thus added is about four times the weight of the *jamak* matter. Having thoroughly mixed these substances with such an amount of cow-dung as is required to give consistency to the material, he forms them into balls of about two or three inches in diameter. He then dries these balls and when perfectly dried they are ready for the third process.

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The *poonoor* employed in the above process is a hard quasimetallic substance that can be purchased from certain grocers at the rate of three or four seers per rupee. It is, they say, nothing but a bye-product in the operation of *rupā-pākāno* by which is meant the operation of chemically purifying silver which has been alloyed with a large amount of copper and other metals. The usual method of conducting this operation in our country is to mix up the alloy with a large amount of lead and after melting the whole mass to blow air from above. [This operation, as also the next one, is practically that of cupellation]. The pure silver, it is found, separates in the course of the operation and collects at the bottom, while the partially oxidised lead, together with the impurities which existed originally in the silver constitutes the *poonoor* of trade. We analysed qualitatively a sample of ordinary bazar *poonoor* by the wet way after dissolving it in nitric acid and found it to contain lead, copper and zinc with traces of silver and iron.

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The third process of the *jamakwala* is the main step in the reduction of gold. He scoops out on the earth in an open place a hollow of the shape of a hemisphere about a foot in diameter, and having thoroughly smoothed the interior of this hollow, he covers it with a layer of slaked lime about half an inch thick. After the lime has dried, it presents the appearance of a course white china vessel, imbedded in the earth. In this the balls prepared by the second process are placed. The *jamakwala* then forms a powerful charcoal fire over it and with two or three large pairs of bellows causes the flame to play on the mass below. The lead of the *poonoor* is soon reduced and dissolves, as it were, the reduced gold, silver and copper. A large metallic mass thus collects at the bottom of the hollow, consisting mainly of lead. The blowing is now continued as hard as possible from above and the metal being oxidised to litharge begins to be blown off. The process must be continued till the whole of the lead has passed off and a mixture of gold, silver and copper remains behind. Care should always be taken in this operation to see that the last trace of lead is thoroughly got rid of; for nothing affects so much the ductility and malleability—virtues most important for the purposes of the goldsmith—of gold as a mixture ever so little of lead. Thus "one two-thousandth part renders the metal too brittle for rolling and its very fumes produce a serious effect upon it."'¹

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¹ Maunder's Treasury of Science, Article : Gold.

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Such is the tedious length and such the laborious and complicated nature of the processes by which the *neharwala* and the *jamakwala* extract precious metal from the large heaps of rejected sweepings and dirt and bye-products of the goldsmith's workshop. But their labours have only the empirical experience of years to guide them and not the acuteness of a well trained scientific mind; and accordingly we find that a large portion of their work is directed to achieve in a laborious and round-about way an object which a slight knowledge of chemistry enables us to secure in the simplest manner imaginable.

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With a view to shorten the labours of the *jamakwala* as far as possible, we began a series of experiments, investigating the properties of the *jamak* and trying to find out the easiest mode of extracting gold therefrom. As the results of our experiments we have found that, working on ordinary plans in the wet way, we can recover an amount of gold, which is equal to, if not in all cases greater than, the quantity which the *jamakwala* can obtain by his expensive and protracted methods.

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We need scarcely give the properties and the constituents of the various specimens of *jamak* which we obtained from the bazar from time to time for experimental purposes. The way in which a *jamak* is formed having been before described in full, the results of analyses will be nothing but tedious. It will be sufficient to observe that in all cases the *jamak* was a clear greenish-yellow liquid of rather thick consistency with a large mass of grey solid matter at the bottom consisting almost wholly of soluble saline matter.

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It may be also added that among bases, silver, copper, zinc, gold, aluminium, potassium and sodium were the principal ones that were found; while amongst the acids present, nitric, sulphuric and hydrochloric were recognised in large quantities. Traces of free chlorine could also be found in some of the solution, while perceptible amounts of iron were found in almost all.

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The microscopic appearance of *jamak* may be interesting as showing the exact state in which gold exists in the solution. With this view we examined under a miscroscope (magnfying 375 times) a drop of a clear solution of *jamak* as well as an amount of the solid saline matter lying at the bottom. The appearance, in both cases was the the same, only in the latter the crystals were more numerous and closer together. The octahedra of alum with occasional facets of cubes, the long furrowed and rhombic prisms of nitre and the cubes of common salt were very prominent. Between these, in numbers far less, could be discovered long, transparent needles. These were most probably crystals of double chloride of gold and sodium which is invariably formed when a solution of auric chloride is mixed with chloride of sodium. The constitution of this substance is AuCl₃. NaCl + 2H₂O, and it is the commercial "non-deliquescent chloride of gold" which is ordinarily sold in one gramme tubes.

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Besides the above crystals, we frequently found amorphous particles, wholly or partially opaque. Those that did not transmit light at all were probably particles of dust or other earthy matter which were present in the ingredients in the shape of impurities. But there were others which transmitted a beautiful green light and these were likely to be fine particles of gold. As these were rather few in number, it might be inferred that in the jamak, gold existed chiefly in combination. It is also probable that the greatest part exists as NaAuCl₄ + 2H₂O.

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From a liquid containing such a variety of substances in solution as the jamak does, it is no doubt a difficult task to precipitate the gold which is present perhaps in the minutest quantity of all.

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The reducing agents that are mentioned by chemists as suited for reducing gold from solutions are exceedingly numerous. Of those that are practically employed, the pricipal ones are ferrous sulphate, oxalic acid, sulphurous acid metallic iron. We tried each of these in a large number of cases and found that ferrous sulphate gives the best result of all. The reaction that takes place during reduction by ferrous sulphate is sometihng like the following :—

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2AuCl₃ + 6FeSO₄ = 2Au + 2Fe₂ (SO₄)₃ + Fe₂CL₆. The gold is precipitated as a fine, heavy, black powder and easily settles at the bottom.

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At first we used the pure material obtained from the chemists for precipitating jamak; but afterwards found that the crude article of the bazar, after being dissolved in water and filtered, yields a solution which serves equally well.

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This makes the process a matter of very little expense and with an anna worth of good crystals of hirakash (the Bengali name of ferrous sulphate), a jamak containing 8 annas weight (for about Rs. 14 worth) of gold can be satisfactorily extracted.

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We are far from thinking that in our experimental attempts to extract gold, we were able to catch the whole of the material that was present in the solution. It is very probable that in the fine state of division, in which the precipitation takes place, a considerable amount of the metal is washed away in the process of collection. But this loss is due to causes of a mere physical nature and can be prevented to a large extent by the use of better and more refined instruments.

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