THE MICROSCOPE IN CHEMISTRY. Ill 



Lead. Sulphuretted hydrogen gives a black amor- 

 phous deposit. Sulphuric and hydrochloric acids yield a 

 white precipitate. Chloride of lead crystallizes in needles. 

 Iodide of potassium gives a bright yellow precipitate, sol- 

 uble in boiling water, and crystallizing in. six-sided plates. 

 Bichromate of potassium yields a bright yellow amor- 

 phous deposit. 



Copper. Sulphuretted hydrogen gives a brown or black- 

 ish deposit ; ammonia a blue or greenish-blue amorphous 

 precipitate, or in dilute solutions a blue color to the liquid ; 

 caustic alkali, a similar precipitate, which on boiling in 

 excess of reagent becomes black, but if grape-sugar, or 

 some other organic agents, be present, a yellow or red 

 precipitate of suboxide of copper occurs. Arsenite of 

 potassium produces a bright green. 



Zinc. Sulphuretted hydrogen gives a white amorphous 

 deposit the only white sulphuret. Alkalies produce a 

 white hydrated oxide of zinc. 



ALKALOIDS. 



The editors of the Micrographic Dictionary refer to a paper 

 of Dr. T. Anderson, in the Edinburgh Monthly Journal, 

 where he shows that the microscope readily distinguishes 

 the more common alkaloids from each other by the form 

 of their crystals and of their sulphocyanides. The alka- 

 loids are first dissolved in dilute hydrochloric acid, then 

 precipitated on a glass plate with a solution of ammonia, 

 or if the sulphocyanide is required, with a strong solution 

 of sulphocyanide of potassium. It may then be placed 

 under the microscope. The solution should not be too con- 

 centrated. This branch of investigation has been greatly 

 promoted by the elegant work of Dr. Wormley, already 

 referred to, on the Microchemistry of Poisons. 



Atropin. Ammonia throws down an amorphous pre- 

 cipitate. One grain of a T tJoth grain solution yields to 



