S3 



<Q/i Assaying Silver. 



[April 



salt, the quantity of which is thus ascertained, — viz. As 

 1.000 .* 5-44 ! : 5 = 0.027 the quantity of salt required. If 

 the solution be too strong, then a less quantity of it than 

 1 .000 grains will neutralize the silver ; suppose 998 grains 

 are sufficient, then it is obvious that 2 grains of distilled 

 water added to 998 of the solution is all that is wanted to 

 make it of the standard strength. 



19. Having prepared a sufficient stock of the standard 

 solution, its use in assay is plain. Suppose the assay pound 

 (10 grains) of silver to be divided into 100 parts, and that 

 the silver to be assayed contained 81 pure silver and 19 

 alloy. Then 810 grains of the solution would precipitate it, 

 and the quantity of the solution expended would be cor- 

 rectly indicative of the true quality of the bullion. Nor is it 

 of any consequence whether fractions occur or not, for if the 

 silver was 71.54 touch, the expenditure of the solution would 

 then be 715.4 grains ; its indications are therefore perfect, 

 and even with a moderate degree of skill in manipulation, 

 the out-turn exhibited by this mode of assay, may, I appre- 

 hend, be depended on to a far greater degree of accuracy 

 than the process by fire. I have made several trials with it 

 on silver of known fineness, and found it come out correct 

 within a two part, on the principle of using 1 .000 grains of 

 the solution. But if the quantity of water was increased, 

 only retaining the same weight of salt, as much greater pre- 

 cision of result could be obtained, as might be thought 

 desirable. 



20. The only practical objection that occurred to me in 

 pursuing my enquiries on this subject was, the tediousness of 

 weighing and of repeated testings ; and the time occupied 

 after each testing, particularly when near the point of satu- 

 ration, before the mixture became clear enough to try it 

 again. But I am informed by a gentleman who was two 

 months at Paris, to learn this method of assay, that neither 

 tediousness nor delay is there experienced, and that the 

 assays are made with sufficient rapidity for the requirements 

 of practice. They do not, however, now weigh the solution 

 of salt, but have their glasses so proportioned and graduated 

 that the quantity expended, can be read off at sight, which is 



