38 THE ALBUMINS. 



albuminous material is treated with 5-10 drops of a 5 percent, solu- 

 tion of p-dimethyl-amino-benzaldehyde (in 10 per cent, sulphuric 

 acid) ; upon the further addition of concentrated sulphuric acid 

 (drop by drop, quick shaking) a reddish violet results, which soon 

 changes to a beautiful dark violet. On spectroscopic examination a 

 broad band is seen in the orange, and a second one, less distinct, in 

 the green portion. 



5. Liebermann's Reaction. The albuminous material after ex- 

 traction with hot alcohol and subsequently with ether (to remove 

 fats) is boiled for a few minutes with concentrated hydrochloric 

 acid to which a drop of concentrated sulphuric acid has been added. 

 The albumin passes into solution and the fluid assumes a deep-blue 

 or violet-blue color. 



The reaction is likewise a furfurol reaction, and has also been 

 ascribed to the simultaneous presence of a carbohydrate and an 

 oxyphenyl group. Like the Adamkiewicz reaction, it may be 

 dependent upon the tryptophan complex. 



6. Molisch's Reaction. A small amount of the albuminous material 

 is suspended in about 1 c.c. of water, treated with a few drops of a 

 15 per cent, alcoholic solution of a-naphthol, and underlayed with 

 concentrated sulphuric acid. A violet color results at the zone of 

 contact, and is assumed by the entire bulk on shaking. Upon the 

 addition of alcohol, ether, or caustic alkali it turns to yellow (on 

 standing). 



Thymol can be used in the place of the a-naphthol ; it gives a 

 carmin color, which on dilution turns to green. 



Like the two preceding reactions this one also is a furfurol reac- 

 tion ; but unlike the others it is referable exclusively to the pres- 

 ence of a carbohydrate group. It is positive with most albumins, 

 but negative with casein. 



7. The Sulphur Reaction. A small amount of the albuminous 

 solution or suspension is treated with an excess of a concentrated 

 solution of sodium hydrate and a few drops of lead acetate solution. 

 On boiling, according to the amount of sulphur present, the entire 

 fluid turns a more or less marked brown, and on standing a precipi- 

 tate of sulphide of lead results. 



The reaction is referable to a sulphur group, which is present in 

 the albuminous molecule as a cystin radicle. As all albumins con- 

 tain sulphur it is obtained with all, though to a more or less marked 

 degree. 



Structural Composition. Our knowledge of the structural com- 

 position of the albumins is largely the outcome of a study of the 

 decomposition-products obtained by hydrolysis, with boiling mineral 

 acids and alkalies, by boiling with water under pressure, and by 

 digestion with proteolytic ferments. As a result it has been possible 

 to establish the existence in the albuminous molecule of certain 

 radicles which, with few exceptions, are common to all forms. 

 The physical differences of the various forms are probably the 



