130 PROTEIDS. 



2. MUlon's reaction. Add 5 or 6 drops of the reagent (acid 



nitrate of mercury) a white pp occurs which heating 

 increases, and ultimately turns to a dull brick red. In 

 weak solutions a red colour may be the only token of 

 a reaction. (Tyrosine, Kiihne.) 



3. Piotrowski's reaction. Add 2 drops of CuSO 4 solution, 



then sufficient KOH or NaOH solution, until the white 

 pp occasioned by the metallic salt is redissolved in the 

 organic solution and a transparent bluish-violet colora- 

 tion is produced. Perform a control test with water 

 and observe that the pp of hydrated oxide of copper 

 which takes place upon the addition of the alkali does 

 not dissolve. This test is also known as the Biuret 

 reaction, because of its resemblance to that obtained with 

 urea. 



Reaction with mineral acids. (H 2 NO 3 , H 2 SO 4 , HC1.) 



4 Add 2 drops of HNO 3 a white pp results. Or by the 

 contact method (Heller's test) pour HNO 3 into the tube 

 to a depth of 2 cm , incline it and flow an equal quantity 

 of the fluid quietly upon the acid, a cloud will form at 

 their junction. If the solution be poor in proteid the 

 cloud will disappear on agitating the fluids together. 



Effects of metallic salts, &c. 



5. Add 2 drops of acetic acid, then 2 CC or 3 CC of ferrocyanide 



of potassium, there is a white pp. 



6. Add 2 drops of acetic acid and one-third volume of saturated 



solution of picric acid] a white pp results. 



7. Mercuric chloride. A few drops produce a white pp. 



A number of other metallic salts do the same. 



