ALBUMINS. 39 



79. Acidify the solution with acetic acid and add a 

 few drops of potassium ferrocyanid. A white precipitate is 

 formed. 



The two last reagents fail in case of the peptones. 



80. Add an excess of Millon's reagent and boil. A 

 red color is produced with all albuminous compounds ex- 

 cept antipeptones. 



81. Many of the albuminous compounds are also precipi- 

 tated by, (1) trichloracetic acid; (2) metaphosphoric acid; (3) 

 alcohol or ether; (4) from solutions acidified with HC1 or HNO 3 

 by potassium mercuric iodid or phosphotungstic acid; (5) from 

 acetic acid solutions by picric or tannic acid; (6) from weakly 

 alkaline solutions by salts of mercury and some of the other heavy 

 metals. Try these. 



No reaction is characteristic in itself; therefore in test- 

 ing for these bodies a number of tests should ~be tried. 



ALBUMINS. 



The albumins are soluble in water. They are not pre- 

 cipitated by dilute acids or alkalies. They are precipitated 

 by saturation with ammonium sulphate and by some of the 

 salts of the heavy metals, such as mercuric chlorid and 

 salts of copper, silver, and lead. For this reason albumin 

 is successfully used as an antidote for poisoning by many 

 of these metallic salts. By the action of acids it is con- 

 verted into acid albumin and by the caustic alkalies into 

 alkali albumin. 



There are several different varieties of albumin usually 

 named from their sources, such as the serum-albumin of 

 the blood; egg-albumin; and the albumin of milk, or 

 lactalbumin. We know that these are not the same sub- 

 stances from their physiological action, as well as from 

 some chemical and physical properties. If, for example, 



