404 Miscellahebus Intelligence. 



Cooper's hands." But this I know, that if all the substances be 

 pure, it cannot fail in any one's. To a neutral solution of nitrate 

 of zinc, I added pure ammonia, just sufficient to re-dissolve the 

 precipitate it at first occasioned. A solution of pure potassa 

 (prepared by Mr. Garden,) was then added, drop by drop, which 

 at first occasioned a little cloudiness, that disappeared, on agi- 

 tating the vessel ; more alcali reproduced a slight precipitate, 

 but a small excess immediately and perfectly re-dissolved it. 

 The solution remained quite clear, without the slightest deposit, 

 after standing eighteen hours in a close stopped phial ; it was 

 then exposed in a small precipitating glass to the air for twenty- 

 two hours longer, at the end of which time the fluid was still 

 perfectly clear, but a small quantity of crystalline matter had 

 collected at the bottom of the jar. When a similar experiment 

 was made with potassa, not perfectly pure, a portion of oxide or 

 carbonate of zinc remained permanently precipitated from the 

 first, and its quantity was considerably increased at the end of 

 eighteen hours. Sulphuret of cadmium, dissolved in muriatic 

 acid, and filtered and treated exactly as the nitrate of zinc, gave, 

 with Garden's potassa, a precipitate, which a great excess of the 

 alcali did not re-dissolve. 



A few drops of a solution of nitrate of cadmium were mixed 

 with a large proportion of a solution of nitrate of zinc, and the 

 mixture treated successively with pure ammonia and potassa as 

 before ; an immediate and permanent precipitate ensued on add- 

 ing the potassa, which, when collected, washed, and re-dissolved 

 in muriatic acid, gave, with sulphuretted hydrogen, the peculiar 

 yellow precipitate characteristic of sulphuret of cadmium. 



After all, the simplest method of detecting cadmium is the 

 following, which Dr. WoUastou had the goodness to teach me : 

 Precipitate all the metals by iron which can be so separated ; 

 filter and immerse a cylinder of zinc into the clear solution. If 

 cadmium be present, it will be thrown down in the metallic state, 

 and when re-dissolved in muriatic acid, will exhibit its peculiar 

 character, on the application of the proper tests. — I am, 8^c. 



Montague-place, April 3, 1820. John Geo. Children. 



P. S. Nothing so much assists the young practical chemist as 



