I REACTIONS OF ALBUMINOUS SUBSTANCES 15 



as the reaction becomes alkaline, but the more strongly basic albumins 

 the histones, and especially the protamins are precipitated even when 

 the reaction is slightly alkaline, or at least neutral. With an excess 

 of the reagent, the albumins proper remain precipitated, but peptones 

 and some of the albumoses pass again into solution. (See Chapter V.) 

 The most important alkaloidal reagents are : 



Phosphotungstic acid } ,, 



. , f These three precipitate peptones and 

 Phosphomolybdic acid r , . 



I are used frequently. 

 Tanmc acid 



Ferrocyanic acid, usually employed in the form of acetic acid 

 + potassium ferrocyanide. It is used clinically as a test for 

 albumin. 



Trichloracetic acid. 

 Picric acid. 



Picrolonic acid is 1 p-nitrophenyl-3 methyl-4 nitro 5 pyrazolon, 

 C 10 H 8 N 4 5 or 



N0 2 . C 6 H 4 . N 



/\ 

 N C. OH 



I! I! 

 CH 3 C C.N0 2 . 



It was first recommended by Knorr L for the isolation of hexone-bases, 

 in particular for arginin and histidin, as the lysin compound is 

 soluble. To free the bases from picrolonic acid, H 2 S0 4 is added to 

 the hot watery solution of the bases, when on cooling the picrolonic 

 acid separates out. The last traces of it are then removed with ether. 



Iodine -hydriodic acid ; iodide of mercury, iodide of bismuth, 

 iodide of cadmium in hydriodic acid, employed usually in the form of 

 iodine -potassium iodide, iodide of mercury -potassium iodide, etc. + 

 hydrochloric acid. Iodide of mercury + iodide of potassium in hydro- 

 chloric acid is known as Briicke's reagent. 



Platinum chloride, metaphosphoric acid, tungstic acid, and allotelluric 

 acid precipitate also according to Mylius, 2 and Heidenhain 3 has shown 

 that most of the acid aniline-dyes precipitate, and that some of these, 

 e.g. violet black, ponceau, palatin red, and neucoccin, are the most 

 sensitive of all precipitating agents, if the reaction be acid. Some of 

 the complex organic acids of unknown constitution, such as nucleic, 



\i 



1 Knorr, Bcr. d. deutsch. Ghem. Oes. 30. 909 (1897). See also M. Schenck, ZeiL 

 f. physiol. Ghem. 44. 427 (1905). 



2 F. Mylius, ibid. 36. I. 775 (1903). " 



J 3 M. Heidenhain, Pfluger's Arch./, d. ges. Physiol. 90. 115 (1902). 



