H CHEMISTRY OF THE PKOTEIDS CHAP. 



3. Mercuric chloride. It precipitates, according to Kiihne, 1 Neu- 



meister, 2 and Siegfried, 3 even the peptones. 



4. Lead acetate, basic and neutral ; it has been recommended by 



Hofmeister 4 as a very perfect precipitant. 



5. Zinc acetate, introduced by Abeles. 5 



6. Uranyl acetate was employed by Jacoby 6 and G-lassner 7 for 



purifying ferments. 



7. Salts of platinum, cobalt, and many other heavy metals were 



investigated by Chittenden and Whitehouse. 8 



In addition to the heavy metals, albumins are also precipitated by 

 a number of organic colour- bases. Mathews 9 and Heidenhain 10 

 obtained marked precipitation with malachite green, brilliant green, 

 new fuchsin, auramin, phenosafranin, and rosaniline acetate ; more 

 feeble precipitation with Nile blue, vesuvin, thionin blue, toluidin 

 blue, methyl green, methyl violet, chrysoidin, neutral red, and neutral 

 violet. For a fuller account see p. 225, and especially Mann's 

 Physiological Histology, 1902, pp. 452-459 (Clarendon Press). 



A behaviour analogous to that of the colour -bases is shown by 

 some basic albuminous bodies, namely, the histones and the protamins, 

 which precipitate other albumins from alkaline solutions. 



2. Precipitation by means of Acids 

 The Alkaloidal 



Being amino-acids, albumins are potential bases. They are pre- 

 cipitated by a series of complex organic acids, the so-called ' alkaloidal 

 reagents ' (Mylius n ). As albumins are very feeble bases, the salts formed 

 by their union with the alkaloidal reagents undergo a hydrolytic 

 dissociation when they are dissolved in water. Thus phosphotungstate 

 of albumin is dissociated secondarily by the ions of the water, and can 

 therefore be rendered permanent only in the presence of an excess of 

 phosphotungstic acid. As a rule the precipitate is dissolved as soon 



itf.^ fefoyt'ALA/' ,j<g& 



^ ! W. Kiihne, Zeitschr. f. Biolog. 22. 423 (1885). 



' 2 K. Neumeister, ibid. 26. 233 (1890).- ^^ 

 ' 3 M. Siegfried, ZgUschr.f. physioL Chem. 35. 164 (1902). 

 J 4 F. Hofmei^C3w2r^ 288 (1878). ~" 5 M. Abeles, ibid 15. 495 (1891). 



- 6 M. Jacoby, ibid. 30. 135 (1900). 



* 7 K. Glassner, Hofmeister s Beitr. I. 1 (1901). 



8 K. H. Chittenden and H. H. Whitehouse, Maly's Jahresber.f. Tierchemie, 17. H 

 (1887). 9 Albert Mathews, Amer. Journ. of PhysioL p. 445, July, 1878. 



' ^ 10 M. Heidenhain, Pflugers Arch.f. d. ges. PhysioL 9O. 115 (1902). 



11 F. Mylius, Ber.'d. deutsch. chem. Ges. 36. I. 775 (1903). 



