1870.] On the Method of Assaying Silver. 379 



range of this error ought not, however, to exceed jV dwt. (6 grs.) in 

 the lb. Troy, or say 2 parts in 1000 ; so that this method is suffi- 

 ciently accurate for keeping a coinage tolerably close to " Stand- 

 ard" and even well within* the legal limits on either side of it. 



The assay report furnished by it, however, is too remote from 

 accuracy, i. e., is not within sufficiently narrow limits to fairly re- 

 gulate the valuation of merchants' bullion with satisfaction to 

 seller or buyer, the latter being, in this country, almost invariably 

 the Mint.f 



The above was the method of assay prevailing in this Mint up to 

 1850. Though it is still practised by many English assayers of 

 great skill, it has been almost entirely superseded on the Conti- 

 nent in consquence of its short-coming by one contrived by Gay 

 Lussac, which is less dej)endent on the individual operator. 



This, known as La voie humide, or the volumetric process for 

 ascertaining the fineness of silver bullion, consists in precipitating 

 the silver as an insoluble chloride from the solution in nitric acid 

 of a certain weight of the metal to be examined, and in effecting 

 this by the use of a solution of common salt (chloride of sodium), 

 containing a known proportion of salt ; this is added gradually 

 till just sufficient has been used to throw down the whole of the 

 silver present as chloride : as chlorine unites with silver in defi- 

 nite chemical proportion, the amount of silver present can be easily 

 and accurately estimated by merely ascertaining the amount of 

 salt which has been exactly necessary to convert the whole of it 

 into chloride of silver. 



This is the method practised at the Paris Mint, and by the 

 eminent outside assayers to the Royal Mint of Great Britain, and 

 I believe at most of the European and American Mints. 



* It being impossible in the operations of a mint to produce a certain mix- 

 ture of metals (such as silver and copper) with mathematical accuracy, a 

 certain deviation is allowed above or below the legal standard : In India this 

 deviation or "remedy" in fineness is 1 dwt. in the pound Troy -i, e. 2 |^th 

 part equal to about 4% parts in 1000. 



P. S. Since this paper was read, a Legislative Act of the Government of India 

 has been promulgated which declares that the remedy in fineness is not to 

 exceed 2 thousandths for the Eupee and Half Rupee, and 3 thousandths in the 

 case of the smaller silver coins. 



f i. e. The Mint receives the bullion in bulk and returns it in coin, a certain 

 seignorage to cover expenses being deducted. 



