Chemistry and Chemical Arts. 145 
22. On the Roasting of Copper Ores, (Ann. du comptoir des 
mines de fer, in Sweden.)—Hitherto the Fahlun copper ores have 
been roasted in rectangular spaces, but some recent experiments have 
satisfactorily shown that reverberatory furnaces are the best. The 
ore must be reduced to the state of a coarse powder, in which con- 
dition it requires only eighty eight hours for completing the process. 
m. 
23. Reduction of the Chloride of Silver. (Journ. of Erpmann, 
1833, p. 270.)—The best way of reducing the chloride of silver, is 
that of Monr, which consists in mixing the chloride with one third 
its weight of colophony, and heating the mixture gradually in a cru- 
cible until the flame loses its blue color ; after which, a strong heat is 
applied to melt the reduced silver.—Jdem. 
24. Preparation of the Purple of Cassius for staining glass 
and enamels. (Journ. of Erpmann, 1833, p. 22.)—The nature 
the precipitate obtained by mingling a solution of gold and one of 
tin varies in color and composition, with a multitude of circumstan- 
ces ; in general, itis a mixture of a compound of oxide of gold, and 
of oxide of tin, with metallic gold, and oxide of tin. A composi- 
tion of constant properties, and suited to stain glass and enamels may 
be obtained as follows: 
Dissolve one part metallic gold in four times its weight of nitro- 
muriatic acid; evaporate the solution until a crystalline pellicle ap- 
pears at the surface, decant the red liquor, leave it to solidify by 
cooling, heat the mass with six times its weight of distilled water, 
and filter it, in order to separate a little gold, still in the fluid. Dry 
the crystallized protochloride of tin of commerce, by compressing it 
in bibulous paper, and dissolve one part in four times its weight of 
distilled water, filter the solution rapidly, in order that the basic salt 
may not separate. Finally dissolve one part of gum-arabic in 
two of warm water, and filter the solution through coarse paper. 
Mix twenty eight grammes of this solution with three ounces of dis- 
tilled Water, add to it twenty four grammes of the solution of tin, 
and afterwards twenty three grammes of solution *of, gold. The 
liquid becomes of a reddish brown, and afterwards of a clearer red. 
As the effect of an excess of acid is always injurious, it is well to 
add to the solution of gold, ten grammes of carbonate of potassa, but 
this is not indispensable. The red liquor does not give a precipitate 
Vor. XXVIII.—No. 1. 19 
