THE JOURNAL OF PHARMACOLOGY. 167 



in the form of a powder. Electrolysis of the solution causes a deposit of 

 gold as a black powder, at the positive pole, which after drying assumes 

 a metallic lustre. 



If the original ruby-colored solution is exposed to the atmosphere, cer- 

 tain moulds develop rapidly, and these, strangely, have the property of 

 appropriating gold from the solution. This property in some cases is so 

 highly developed that the solution is entirely decolorized. The mycelium 

 of such moulds assumes a dark red and at times even a black color. It 

 these moulds are allowed to dry on a glass surface, a spot possessing the 

 lustre of gold is produced, which under the magnifier appears like a net- 

 work. If solutions of colloidal tin and colloidal gold are mixed, and di- 

 lute acids are added, precipitation results. The gold in this instance re- 

 tains its fine state of subdivision and consequently its red color, and in 

 this condition is intimately mixed with the tin. This precipitate seems to 

 be identical with the substance known as the purple of Cassius. The ex- 

 periment thus made seems to definitely settle the old question of the com- 

 position of this golden purple. 



G. C. D. 



Soluble Mercury. 



Lottermoser (Phar. Zeitting, 13, p. 519), reports that he has been suc- 

 cessful in his attempt to obtain colloidal mercury, corresponding in char- 

 acter to like modifications of silver and gold recently made. His method 

 of procedure was as follows : Into a very dilute solution of stannous 

 nitrate is poured, very slowly and under constant stirring, a solution of 

 mercurous nitrate, also very dilute. Both solutions are to have a faint acid 

 reaction, only enough free nitric acid being present to prevent the forma- 

 tion of sub-salts. It was found that the tin salt must be used in excess, 

 otherwise the colloidal mercury soon changes. The dark brown solution 

 resulting from above operation is treated with a concentrated solution of 

 ammonium citrate, causing a separation of colloidal mercury, which be- 

 comes apparent by a change in color to black, and the deposition of a very 

 fine black precipitate. The mixture now is kept cool and ammonia water 

 added until all free acid is neutralized. The supernatant liquid is removed 

 by decantation, and the precipitate first allowed to drain on a porous plate 

 and later dried over sulphuric acid in a vacuum exsiccator. The resulting 

 masses have a metallic lustre, and dissolve in water, forming a dark brown 

 solution. Mercuric nitrate may be employed in place of the mercurous 

 salt ; in this case, however, it becomes necessary to use a greater excess of 

 stannous nitrate. The author also states that mercuric acetate may be 

 employed, but that mercurous acetate yields negative results. The col- 

 loidal mercury so obtained always contains a trace of tin, which cannot be 

 removed without altering the product. G. C. D. 



