VOL. LXIX.] PHILOSOPHICAL TRANSACTIONS. 587 



weight could not be ascertained; it did not amount to above 2 or 3 grs. at 

 most. The powder, washed off and dried, weighed 134 grs: these, mixed with as 

 much litharge, and 4 times their weight of fixed vegetable alkali, and J- of wheat 

 flower, and the whole melted, produced a regulus of lead, weighing 80 grs., 

 which, on coppelling with a few grains of silver, and parting in aquafortis, left 

 -Jj^ of a troy grain of gold. It is to be remarked, that in great works, where 

 gold is separated from pieces of crucibles, sand, or other matter, by amalgama- 

 tion, notwithstanding the process be frequently repeated, and with great care, 

 some small portion of the gold still remains; so that the small quantity left in 

 this case might easily have either escaped the mercury, or have been left un- 

 observed in the powder combined with small particles of it. They therefore 

 concluded that in this ore the gold was in its native form, and not mineralized. 



Exp. 3. They examined gold pyrites mixed with quartz, with a deep mag- 

 nifier, and found evidently native gold interspersed. One hundred grains of 

 this ore, were powdered ; and boiled in nitrous acid diluted with water: a solution 

 of iron took place, as in the first experiment. The residuum being exposed to a 

 red heat, there was no appearance of sulphur; the gold was found in such large 

 particles, and so similar to native gold, that they did not think it worth while to 

 apply mercury. The gold being dissolved out by aqua regia, a quantity of 

 quartz and arsenical salt was left. 



Exp. 4. When gold and silver are found in their metallic form, it is not 

 uncommon to find them mixed; but it seldom occurs, that they are mixed in so 

 large proportion as in an ore obtained from Norway, and which was given to 

 Dr. Hunter, by Mr. Fabricius. The ore has the appearance of native silver, 

 in scaly particles, intermixed with a hard quartz, tinged brown, in some parts 

 by iron. Twenty-five grains of the mass, where the metal was in the largest 

 proportion, melted with litharge, alkali, and phlogistic matter, and afterwards 

 coppelled, yielded a globule apparently silver weighing 2 grs. which, being boiled 

 in nitrous acid diluted with water, left full -V of a grain of fine gold. Hence 

 100 lb. of metal obtained from this ore, consists of 72 lb. of silver, and 28 lb. 

 of gold. 



There is an ore of silver which is commonly called vitreous (minera argenli 

 vitrea, or argentum vitreum). This ore has always been supposed to consist of 

 sulphur and silver; because, if sulphur and silver be melted together; they form 

 a mass which resembles it, especially in colour and malleability; but, as they 

 could find no experiment in any author which authorized this conjecture, they 

 determined to endeavour to ascertain it by analysis. Dr. Hunter not refusing to 

 subject the ore to an assay, though scarce and expensive. 



Exp. 5. Fifty grains of this ore broken in pieces, for it was too malleable to 

 be powdered, were boiled in nitrous acid diluted with water; the acid dissolved 



4 F 2 



