SWEAT. 169 



from water and from alcohol, dissolve a small quantity 

 in a very large bulk of water, and apply the following 

 tests. 



a. Add a drop of cuprous chloride in hydrochloric 

 acid ; a bulky white gelatinous precipitate will 

 appear. 



I). Add mercuric nitrate ; an amorphous white 

 precipitate will fall. 



c. Add cupric sulphate ; a precipitate of white 

 microscopic prisms will gradually form, redis- 

 solved by heat and depositing again in oily 

 drops or in crystals on cooling, giving by long 

 boiling a black precipitate of sulphide. 



d. Add ferric chloride ; no reaction if the urea be 

 pure. 



4. Boil a sulphocyanide with nitric acid ; a yellow 

 precipitate of persulphocyanogen will be produced. 



5. To a sulphocyanide solution add ferric chloride ; 

 an intense red colour will be produced. Add a frag- 

 ment of pure zinc, and suspend over it a slip of paper 

 moistened with lead acetate. The paper will be 

 blackened by the evolution of H 3 S. 



6. Add solution of cuprous chloride in hydrochloric 

 acid ; a white granular precipitate will appear. 



Sweat. 1. Notice appearance, smell, acid reaction, 

 and presence of epidermic scales. 



2. Distil down to a third or fourth with a little 

 dilute sulphuric acid. Examine the distillate for 

 volatile acids (q.v.). Digest the residue in the retort 

 with ether. 



