صور الصفحة
PDF
النشر الإلكتروني

This converts the metallic copper into oxide of copper. When cool the mass is boiled, 100 lbs. at a time, in a leaden boiler, for about an hour, with 40 lbs of sulphuric acid and 200 lbs of water. Most of the copper is thus recovered in the state of sulphate of copper solution, which is poured off into tanks to crystallize. What is undissolved by the acid is tile-dried, and a small portion, about ten tola weight, of the residue melted for trial. If the trial ingot is malleable and soft the whole mass may now be melted into ingots to close the account. For although these ingots will be much worse than standard, they are free from lead and devoid of brittleness, and consequently fit for alligation. On the other hand if the trial ingot be brittle the mass should be again roasted and treated with sulphuric acid as before. And according to the original quality of the silver this may need three such operations.

In refining 100,000 Rs. value of such understandard coin, about 90,000 Rs. value will be returned at once refined above standard-5000 will be found in granules--4000 to 5000 will be recovered by roasting and by sulphuric acid, and from 500 to 1,000 will remain as chloride of silver and very finely divided metallic silver, which is slowly deposited from the sulphate of copper liquid, as a white slime or mud, consisting of the chlorides of silver, copper and lead, sulphate of lead and metallic silver. This mud is tile-dried and treated as follows:

100 parts by weight are well mixed with 50 of dried carbonate of soda, and 20 of powdered charcoal, the mixture melted in black lead pots and poured into conical moulds—on cooling a mass of lead containing all the silver is found at the point of each cone. This lead usually contains 20 to 25 per 100 of silver, and the precious metal is extracted by cupellation. The quantity of argentiferous lead to be cupelled from the refinage of 100,000 tolas of silver will range from 2000 to 4000 tola weight. If black lead pots are not available this part of the operation may be conducted successfully in the native cylinder furnace above described, merely substituting cow-dung for the charcoal, and mixing the mass into balls.

By careful attention to the above description no failure or difficulty need be dreaded in large silver refinages. The advantages of the process may be briefly summed up-rapidity, economy, salubrity and safety of the bullion. Before this method was introduced in the Calcutta mint the refinage of silver to the value of a lac of rupees was the work

of six weeks to two months. It can now be effected in four hours. The sulphate of copper removed in clearing up the scoriæ is in another department of the mint brought to yield the copper it contains in an absolutely pure state, so enhanced in value that it sells for 44 Rs. the maund of 100 Troy pounds, and thus pays for the saltpetre, acid, fuel, wages of workmen and melting losses. The poisonous fumes of the lead cupellation are avoided—and the rapidity with which 95 per 100 of the bulion is returned to the mint strong room, being taken there directly from the furnace, reduces the risk of loss by pilfering to an insig nificant amount. The importance of this can only be estimated by those who may bave to manipulate large quantities of bullion with native workmen and overseers, under whose care silver is apt to acquire the volatility of mercury, and disappear in a way that would appal a refiner only accustomed to the habits of the metal in European establishments. Against this cause of loss experience teaches me there is no safeguard but the concentration of the processes under the director's eye, the employment of the smallest possible number of persons in the manipulation, and the return of the bullion under resinage with the least avoidable delay.

[.Assay of silver.] In the commencement of this paper I alluded to our silver standard, and to my desire to afford a few useful hints to officers having bullion transactions with native states. Vast sums are annually paid in native coinages of almost innumerable variety, of which the Nanashaye and Balashaye rupees of Jaloun and the Deb-mohree rupees of Assam may be cited as examples. It may be confidently stated that whatever be the nominal fineness of these coins, the practice of the native mints is to debase as much as possible, and their workmen are moreover well acquainted with all the arts of piekling and blanching, hot stamping, &c. which give the debased coin a most respectable surface. Some ready method of assay, not affecting to be exact, but one closely approximative, would, I have been often assured, be deemed of much utility to many public officers in the transactions referred to. Such a method I take this opportunity to describe, prefixing a few words on the exact systems of assay followed in the mints.

In the English and Indian mints the ancient process of cupellation is followed. Through the great kindness of my friend, Mr. Dodd, the

present Assay Master, I have been enabled to convince myself that in skilful and conscientious hands this method ensures all the accuracy which is required in the operations of the mint and for commercial purposes. Its range of error will not exceed 2 parts in 1000, and be still within the deviation permitted by the law with reference to the impossibility of ensuring an exact mathematical alloy in all minting operations. But this system of assay demands the appliance of so much skill and such cumbrous apparatus that to the experimentalist “ in the jungle” it affords no resource.

The French method, by solution in nitric acid and precipitation of the silver as chloride by common salt, is only applicable where the silver under assay is alloyed with copper only. If it contain lead, mercury, tin or iron, the results are fallacious. I enter upon no details, as I am not addressing these remarks to assayers. It is enough to say that the solution becomes so milky from the presence of chloride of lead, calomel, or peroxide of tin, that it is impossible to see and note correctly when the proper quantity of the salt test-liquor has been added ; or on the other hand, if the experimentalist desires to weigh the precipitate, he is liable to be deceived by the quantity of insoluble chlorides of base metals united with that of silver.

I pass therefore to another and a ready resource, which only requires a Florence flask or two and a little nitric acid for its performance, and by which the experimentalist may proceed as follows:-

Weigh 24 grains of the silver to be examined, and dissolve it by means of one fluid drachm of pure nitric acid, about sp. gr. 1350, and half an ounce (Aluid) of rain or distilled water. When dissolved dilute the fluid to two ounces with distilled water and introduce a clean slip of pure copper. Boil the contents of the flask over a lamp or on a pan of sand over a charcoal fire, so long as silver is deposited on the copper, and until a fresh slip of copper introduced is not tarnished then let the liquid settle, decant the blue liquid, replace with water, decant once more, placing the thumb on the mouth of the flask invert it and let the silver escape upon a small China saucer—let the moisture drain off and dry the silver thoroughly over the hot sand. Weigh it now in your medicine chest scales, which ought to turn fairly to oth of a grain or less. Now if your silver be the Company's standard, the 24 grains (= to 24.00) should give you 22.00. An English shilling

should give 22.20 ; an old Sicca rupee 22.15,---each tenth of a grain being the equivalent of one dwt. If more than 22.00, the silver is better, if less than 22.00, it is worse than our standard. But the silver obtained in this experiment is usually somewhat heavier than it should be, being associated with a little copper. The error is nearly compensated by the slight loss in the manipulation, and moreover it does not amount to more than one dwt. of excess. This

may

be safely allowed for, and the extempore assayer may rest satisfied that he knows the true value of his silver within 1 per 100. Thus for example, he dissolves 24 grains of a Debmohree rupee, and he finds his dry silver weighs 13 grs. It is therefore 9.0 grs. (or 90 dwt.) worse than 22 grs. which should be the standard. Now as 24.0 :: 13.0 :: 100 :: 54.16, or 100 tolas of this silver contain fine silver 54.16 = 59.08 Co.'s Rs. But if an error had occurred increasing the weight of the silver precipitate to 13.20 the per centage of fine silver would be 55.00+1 alloy

to Co.'s Rs. 60, the difference being 0.84 per 100 on the fine silver, or 9-10ths of a rupee.

But in the transactions to which these remarks bear reference an error of even one per 100 at either side is of but insignificant importance, the object being merely to obtain a good approximation, not an absolutely correct result.

The use of pure copper is essential for this simple process, inasmuch as the impurities of the metal usually met with may lead to very deceptive results. I shall be happy to supply any reader of this paper with electrotype copper in sufficient quantity to enable him to try his skill as an amateur assayer—for pure nitric acid I must refer him to the Hon. Company's Dispensary, or to any of the eminent Calcutta druggists.

Observations on the Ovis Ammonoides of HodgSON, by Capt. 7'.

HUTTON, F. G. S. Having lately procured a pair of skins of the (so called) “Oris Ammonoides" of Hodgson, and as the specimens are both in winter pelage, as indicated by the beautifully soft wool under the hair, it may be interesting to compare the description of them with that lately published by Mr. Hodgson, in the Journal Asiatic Society, No. 173. of 1846.

Ovis Ammon" ? Pallas. vel. “0. Ammonoides," Hodgson. The Nian” or “ Nyanof the Bhoteahs.—(Pronounced nasally in one syl. lable.)

Measurement of a male of five years, according to the markings on the horns ;

ft. ins. From nose to base of horns,

1 1 Thence to insertion of tail,

5 Tail to end of hair,

0 3

1

1

Total,

6 5

ft. ins.
Circumference of horn at base,
Length on the curve,

2 10, tips broken. Winter pelage ; above deep brown interspersed with grey, with a distinctly marked darker dorsal line, passing, (as in 0. montana) in a narrow stripe through the disc on the croup, even to the tip of the tail. Sides mixed hoary or slatey grey brown; disc on the croup well defined and dirty white, the hair appearing as if rubbed. The throat and neck beneath to the breast, white, sprinkled with scattered brown hairs; the hair long, bushy and pendent; and from 6 to 7 inches in length, while that of the back is barely 2 inches, except on the dorsal line, where it is 3 inches, and on the ridge of the neck above 31 inches. Tail, above, brown; whitish at the sides, naked beneath. Under parts dirty white; medial line blackish ; outside of the limbs with a dark list ; lips, whitish ; face, paler brown than the body.

Front surface of horns,

3} inches wide. Inner lateral surface,

6 inches wide. Measurement of the bare skull of a male 7 years old ;

ft. ins. Length of face to base of horns,

1 1 Length of horn on the curve,

2 10 Basal circumference,....

1

These horns are weathered and much broken at the tips, and were probably about 3 ft. 3 inches long.

« السابقةمتابعة »