VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 17 1 



the retort was of a gold-colour, and a brown matter was deposited in circles at 

 the bottom of the retort. The strength of the acid was impaired by these re- 

 peated distillations. 



Being thus convinced that in exper. 63 the gold-colour which the acid acquired 

 was no proof of any of the gold having been dissolved by it, he resolved to make 

 other trials. Accordingly, 



Exper. 75. He attempted to dissolve gold leaf and some grains of platina by 

 digesting them in this acid for 6 weeks. On adding salt of tartar, no precipi- 

 tation at first took place; but after subjecting the mixture to digestion, a preci- 

 pitate was thrown down, which being edulcorated and dried was of a white co- 

 lour.* This precipitate he suspected to be of an earthy nature; but the quan- 

 tity was too small to allow him to ascertain to which species of earth it belonged. 

 He supposes it to have been volatilized by the acid of fat. — The solution showed no 

 signs of any metallic impregnation on adding Beguin's volatile tincture of sulphur. 



Exper. 76. He digested for the space of a month 8 gr. of gold calx, obtained 

 by salt of tartar, with 4 oz. of the acid of fat. The greater part of the calx 

 remained undissolved at the bottom of the vessel. But on adding to the filtrated 

 liquor, some of the volatile tincture of sulphur, a bluish grey-colour was imme- 

 diately produced. The liquor being strained and the sediment on the filtre being 

 dried, it appeared of a dirty yellow-colour, denoting the presence of gold. This 

 however was more clearly proved, by evaporating a part of the solution, which 

 then yielded some yellowish brown crystals, of an indeterminate figure. 



Exper. 77. To promote the action of the acid of fat upon gold, he thought 

 of mixing other acids with it. Accordingly to the same quantity of gold calx, 

 he added 40 drops of acid of fat, with which in one vessel were mixed 20 drops 

 of pure nitrous acid, in another 20 drops of spirit of salt. In the first vessel, 

 bubbles of air were immediately extricated, denoting an incipient solution; in 

 the second vessel no change took place. Both vessels were then subjected to a 

 digesting heat, by which the solution in the first vessel was promoted, but in the 

 second no traces of a solution appeared. Of each of these liquors 8 drops were 

 added to 2 separate portions of a diluted solution of tin; the first instantly depo- 

 sited a purple precipitate, the other only became a little turbid, without under- 

 going any change of colour. 



Exper. 78. He was encouraged by this experiment to try whether this acid 

 could not be made to dissolve gold in its metallic state. Accordingly to a bit of 

 gold leaf he added 80 drops of the acid of fat and 20 drops of pure nitrous acid. 

 Its surface was almost immediately covered with air-bubbles, and the solution 



* The same phenomenon was observed when salt of tartar was mixed and digested with acid of fat 

 previously digested with silver and bismuth. 



Z 2 



