Mr. Murdoch on the Impurity of some JDrv^s. 237 



silica 12805 ; peroxide of iron and alumina 11-55 grains ; water 0*51 

 grains. And the results of two analyses were as follow: — 



100- 100-26 



Dr. Thomson having suggested that the mode in which this adul- 

 terated article was manufactured was by mixing together a portion of 

 Armenian bole, chalk and sulphate of barytes, the next object was to 

 examine Armenian bole for the purpose of comparison. 



The following are the results of several analyses of this substance 

 which is used extensively for colouring tooth-powders, &c. by druggists. 

 The fourth analysis was made by my brother, Mr. James Murdoch : — 



III. IV. 



— 49-38 



31- 



/ 30-44 

 t 690 



7-04 

 8-30 

 1-98 



To determine if any silica was contained in the sulphate of barytes 

 of the adulterated calamine, the sulphate was fused with carbonate of 

 soda, the fused mass washed with water until all the sulphate of soda 

 was removed, and then the residue was digested in dilute muriatic 

 acid — a portion of silica remained undissolved: the quantity was not 

 determined. But it is obvious that the calamine contains all the sub- 

 stances existing in Armenian bole, and the conclusion is scarcely 

 avoidable that the colour is caused by the presence of this body 



2. PRECIPITATED SULPHUR. 



This substance — also termed milk of sulphur, and washed sulphur — 

 is properly prepared by boiling sulphur with lime or potash, precipi- 

 tating the solution with muriatic acid, throwing the precipitated sulphur 

 on a filter and washing it. If this form of sulphur were always pre- 

 pared in this manner, no impurity would exist in it. But it has been 

 observed that this article, in London at least, contains always above 

 one-half its wciglit of impurity. To ascertain if this substance in 

 Glasgow was equally impure 58*85 grains were ignited in a platinum 

 capsule, and were found to lose 29- grains. This would make the 



