20 PHYSIOLOGICAL CHEMISTS Y. 



with hydrochloric acid. 9. Precipitation by Picric Acid in solu- 

 tions acidified by organic acids. 



B. Color Reactions for Albuminous Bodies. 



1. Millon's reaction. 1 A solution of mercuric nitrate in nitric 

 acid containing some nitrous acid gives a precipitate in albumin 

 solutions which at the ordinary temperature is slowly, but at the 

 boiling-point more quickly, colored red ; and the solution may also be 

 colored a feeble or bright red, depending on the amount of albumin. 

 Solid albuminous bodies, when treated by this reagent, give the same 

 coloration. This reaction, which depends on the presence of the 

 aromatic group in the albumin, is also given by tyrosin and other 

 benzol derivatives , with a hydroxyl group in the benzol nucleus. 

 2. Xanthoproteic reaction. With strong nitric acid the albuminous 

 bodies give, on heating to boiling, yellow flakes or a yellow solution. 

 After saturating with ammonia or alkalies the color becomes orange- 

 yellow. 3. Adamkiewicz' reaction. If a little albumin is added to 

 a mixture of 1 vol. concentrated sulphuric acid and 2 vols. glacial 

 acetic acid a reddish-violet color is obtained slowly at ordinary 

 temperatures, but more quickly on heating. Gelatine does not give 

 this reaction. 4. Biuret test. If an albumin solution be first 

 treated with caustic potash or soda and then a dilute copper 

 sulphate solution be added drop by drop, first a reddish, then a 

 reddish-violet, and, lastly, a violet-blue color is obtained. 5. Al- 

 bumin is soluble on heating with concentrated hydrochloric acid, 

 producing a violet color, and when the albumin is first boiled with 

 alcohol and then washed with ether (LIEBERMANN) it gives a 

 beautiful blue "solution. 6. With concentrated sulphuric acid and 

 sugar (in small quantities) the albuminous bodies give a beautiful 

 red coloration. These color reactions apply to all albuminous 

 bodies. 



The delicacy of the same albumin reagent differs for the differ- 



1 The reagent is obtained in the following way : 1 pt. mercury is dissolved 

 in 2 pts. of nitric acid (of sp. gr. 1.42), first when cold and later by warming. 

 After complete solution of the mercury, add 1 volume of the solution to 2 

 volumes of water. Allow this to stand a few hours and decant the super 

 natant liquid. 



