192 Miscellanies. 



14. Purple powder of Cassius. — M. Buison states that in prepar- 

 ing this substance, he found that the solution of gold always contains 

 the same muriate, though it may be mixed with more or less acid ; 

 but he observes, that the solution of tin, even when well prepared, 

 contains two difierent muriates and it is upon their co-existence, with- 

 in certain limits, that he conceives the goodness of the solution to be 

 owing. The experiments upon which this opinion are founded are the 

 following. 



1st. The solution of proto-muriate of tin, as neutral as possible 

 when mixed with a solution of gold, gives a maroon, brown, blue, 

 green, or metallic precipitate, according to its concentration and pro- 

 portion, but the color is never purple. 



2d. Pure per-rauriate of tin, whether acid or not, produces no 

 change in the same solution of gold, whatever be the proportions em- 

 ployed. 



3d. A mixture of one part of proto-muriate nearly neutral, and two 

 parts of per-muriate of tin, with one part of muriate of gold, instantly 

 occasions a fine purple color. Founded on these facts, M. Buison gives 

 the following process for obtaining the purple powder : 



4th. Dissolve about 15 grains of granulated tin, in muriatic acid, 

 either with or without heat, taking care that the solution is neutral. 



5th. Prepare a solution of per-muriate of tin by dissolving about 

 30 grains of tin in a sufficient quantity of aqua-regia, composed of 

 three parts of nitric acid, and one part of muriatic acid ; taking care 

 that the solution is neutral, and free from proto-muriate which is 

 determined by its giving no precipitate with a solution of gold. 



6th. To prepare the solution of gold, dissolve about 108 grains of 

 gold in aqua-regia, composed of one part of nitric acid and six parts 

 of muriatic acid ; the solution should be nearly or quite neutral. 



Dilute the solution of gold, so that a pint of it contains about 15 

 grains of the metal. Pour in the per-muriate, till the required tint 

 is produced, remembering that the proto-muriate causes a brown, and 

 the per-muriate a violet color, and intermediate proportions give a red. 

 Wash the precipitate as quickly as possible, that no action may take 

 place between the salts of tin and the precipitate, which alters its col- 

 or. The purple powder of a fine tint yielded by analysis ; 



Metallic Gold, - 38.5 



Peroxide of tin, 65.9 



Chlorine, ....--- 5.3 



99.6 

 Loss, 4 



100.0 



(Jour, de Pharmacie, October, 1830.) — Idem^ 



