OF ARTS AND SCIENCES. 59 



bonate of lead in nitric acid for the final lead determination, was in 

 each case incinerated, and then fused with carbonate of soda before 

 the blowpipe. A distinct button of metallic gold was obtained in every 

 instance. The amount of gold obtained varied, however, to a very 

 considerable extent : it was abundant in the American and Spanish 

 coin, less was observed in the English and Mexican, and but little in 

 the French coin or the American fine silver.* 



The silver of the French coin was undoubtedly prepared by the 

 sulphuric-acid process,! in which the granulated alloy of silver, gold, 



* Besides the quantitative analyses recorded above, which have been made by 

 this method, it should be mentioned, that in several qualitative experiments upon 

 American coins, by the method as described or slightly modified, indications of 

 lead were obtained in every instance. The same remark is true of two qualitative 

 analyses, — one of a dime and another of a quarter-dollar, — made as follows : 

 the coin having been dissolved in nitric acid, and the insoluble black residue of 

 sulphide of silver and a little gold separated by filtering, the solution was mixed 

 with pure acetate of soda (see Fresenius, op. cit., p. 428, § 163, 1. y) to prevent 

 precipitation of chloride of lead in subsequent operations, and the whole heated 

 over the water-bath ; the silver was then precipitated with dilute chlorhydric acid, 

 and the chloride of silver collected upon a filter and washed. Through the filtrate 

 sulphuretted hydrogen was passed, the mixed sulphide of copper, lead, and gold 

 collected upon a fiilter, treated with nitric acid, the acid solution evaporated to dry- 

 ness, the residue taken up with water, and the solution filtered ; in the filtrate 

 lead was detected, while the residue contained gold. 



With regard to this residue of gold, which has also been alluded to in the text, 

 it should be remarked that it has been entirely neglected by many analysts who 

 have published determinations of the amounts of gold in various silver coins. In- 

 deed, it would appear as if the fact were not generally known to chemists, that 

 nitric acid can dissolve a little gold (as it can platinum), when an alloy containing 

 a small quantity of gold is treated with this acid (compare Mulder, op. cit., p. 159). 

 Another common error of analysts has been, to class as " gold " the dark-colored 

 residue which is usually left when silver coin is dissolved in dilute nitric acid. 

 This precipitate does, in fact, generally contain a little gold, though in our own 

 experiments by far the larger portion of this metal passed into solution in the 

 nitric acid, and was separated at a subsequent stage of the analysis, as has been 

 described; Gay Lussac (Ann. Ch. et Phys., 1836, [2.] LXIII. 334) long ago 

 showed that it is principally composed of sulphide of silver ; to which fact atten- 

 tion has also been called by Mulder, in his excellent little treatise, just cited, 

 p.- 178. 



t See D'Arcet in Dingler's Polyt. Journ., 1828, XXVIII. 3; from Annates 

 Mensuelles, Mai, 1827, p. 131. Also, Ure's Dictionary of Arts, &c., 4th edit., (Bos- 

 ton, 1853,) II. 543. Dumas's Traite de Chimie Applique'e aux Arts, (Paris, 1833,) 

 IV. 464. 



