1870.] On the Method of Assaying Silver. 383 



(each sample in duplicate) in small shallow saucers of polished 

 copper and so brought in batches of 40 on a board, containing in 

 numerical order receptacles for the little saucer, to the Assay- 

 Master who, in the delicate assay balance, exactly brings each 

 sample to the one required weight.* 



As each sample is weighed, it is transferred from the platinum 

 skiff of the balance to a bottle on the left hand of the assayer, by 

 means of a small copper funnel. The bottlesf for this purpose 

 are held in readiness for the musters by an assistant and, on receiv- 

 ing them, are removed into the Laboratory in batches of six. 



On being taken to the laboratory, they are ranged on a circular 

 platform or turn-table and there one of the (European) assistants 

 adds by means of a pipette 1^ drachms of nitric acid to each 

 bottle, which are then (without their stoppers) transferred to a 

 sand-bath and exposed to a considerable degree of heat, till solu- 

 tion of the contents is effected. 



The specific gravity of the nitric acid used is generally 1200, 

 /. e. in the case of known alloys of only copper and silver, such as 

 the standard meltings, coins, &c, but when the nature of the alloy 

 is uncertain, such as bazaar silver, or some sycee, (where the 

 presence of mercury may be suspected), a stronger acid of sp. gr. 

 1320 is used. It has been found too by experience that the chlo- 

 rides from fine bar silver eventuate better, when the solution has 

 been effected in the stronger acid. 



When the samples have been completely dissolved, J the bottles 

 are brought back to the platform and there each receives through 

 a glass funnel § about six ounces of cold distilled water. 



There is then added to each bottle through a glass pipette, as 

 before, 1£ drachms of hydrochloric acid, sp. grav. 1060, which 

 immediately converts the silver present into the characteristic white 

 precipitate of chloride of silver, which forms in slow-falling curdy 

 volumes. 



* The amount of this weight will be more particularly referred to further on. 



f The chief appliances will be described more fully in an appendix. 



% A slight residuum of gold, as a black powder is very generally seen. 



§ The portion of this which enters the neck of the bottle is protected, or 

 sheathed, with an inch of India rubber tubing to prevent chipping, if struck 

 against the neck of the bottle. 



49 



