98 ' PHILOSOPHICAL TRANSACTIONS. [aNNO 1791. 



effects of fire. A striking example of the power of fire to change the colour of 

 bodies, by merely increasing their specific gravity, isafibrded by the operation of 

 quartation, in which process, the silver being parted, the gold is left of the 

 colour of copper ; but, by exposure to a due degree of fire, it is changed to its 

 well-known yellow colour, without undergoing any alteration except an increase 

 of specific gravity. 



To elucidate the nature of the insoluble and infusible part of James's powder, 

 I made the following experiments, in which I particularly had in view to deter- 

 mine whether several antimonial calces be wholly soluble in acids. 



Exper. Q. (a) Needle-like crystals of Algaroth powder dissolved readily and 

 totally in about 30 times their weight of marine acid, (b) Part of the same 

 parcel of crystallized Algaroth powder was calcined for above 2 hours, during 

 which time it was exposed to as great a heat as it would bear without melting, 

 and during which time it was constantly raked about. Nearly half of this cal- 

 cined calx readily dissolved in marine acid, and by boiling the remainder in a pro- 

 portionally much greater quantity of the same acid, great part of it was dis- 

 solved, and the small part which still resisted solution could not be dissolved in 

 above 100 times its quantity of hot aqua regia. This indissoluble part afforded 

 regulus with tartar by means of heat applied with the blow-pipe, (c) White 

 flowers of antimony generally left a residuum that, was either insoluble, or dis- 

 solved with great difficulty, and in a small proportion, in marine acid or aqua 

 regia ; yet this residuum was reducible. Some parcels of this calx totally dis- 

 solved, (d) A little of the antimony, long calcined in a former experiment, and 

 afterwards melted into a yellow mass, Exper. 8 (a), would only partially dissolve 

 in marine acid and aqua regia ; but the copious residuum it left was reduced, (e) 

 Equal weights of crystals of Algaroth powder and calcined bone mixed together, 

 dissolved totally and readily in marine acid. This shows, that disengaged phos- 

 phoric acid does not precipitate antimonial calx when marine acid is present, 

 (f) The calx antimonii nitrata of the Edinburgh Dispensatory, argentine flowers 

 of antimony, hyacinthine glass of antimony, and calx precipitated from antimo- 

 nial tartar by alkali of tartar, all dissolved readily and wholly in marine acid ; 

 but, (g) Diaphoretic antimony left a residuum wliich mixed with tartar formed 

 metallic grains under the flamoapplied by means of the blow-pipe, (h) Any of 

 the above soluble antimonial calces by further calcination with air and fire become 

 more difficultly soluble, or partly indissoluble. 



The next experiments were made principally for the purpose of knowing 

 whether antimony calcined with vitriolic selenite, calcareous earth, and siliceous 

 earth, would aftbrd the same sort of calx as antimony calcined with bone-ashes. 



Exper. lO. 1500 grs. of well burnt and dry plaster of Paris, mixed with as 

 much pulverized antimony, were calcined together in the same manner as the 

 mixture for making Lile's powder, Exper. 3. In I an hour the sulphureous 



