176 CHEMISTRY OF THE PROTEIDS CHAP. 



slightly soluble globulins, and thereby causes the latter to become 

 precipitated. Acetyl-derivatives of the albumoses have been prepared 

 by Schrotter. 1 



Peptones. All substances which cannot be salted out are called 

 peptones, and these are further characterised by giving the precipita- 

 tion-tests only to a limited extent. Of the various colour -tests, 

 they constantly give the biuret-reaction, but only occasionally the 

 other colour-tests. 



Peptones are colourless, dry powders, according to Siegfried 2 and 

 his pupils. 3 They are very soluble in water, also in glacial acetic acid, 

 and in all salt solutions ; partly soluble in 96 per cent alcohol ; in- 

 soluble in all the other solvents in general use. All give an intense, 

 pure red biuret-reaction even when greatly diluted, and also the 

 xantho-proteic reaction ; while the other colour-tests may or may not 

 be given, according to the nature of the peptone under examination. 

 Peptones contain no sulphur. The heavy metals produce no precipi- 

 tation ; amongst the alkaloidal reagents, phosphostungstic and picric 

 acid when used in concentrated solutions give a precipitate which dis- 

 appears on heating and reappears on cooling. 



Tannic acid causes in concentrated solutions a precipitate, which is 

 soluble in acetic acid. Bin-iodide of mercury, bin-iodide of bismuth, 

 and iodine in potassium iodide solutions, and, further, trichloracetic 

 acid, 4 do not precipitate in watery solutions, but do so in concentrated 

 calcium chloride, 5 calcium nitrate, 5 and ammonium sulphate 6 solutions, 

 according to Kiihne, 4 Pick, 5 and Cohnheim and Krieger. 6 Mercuric 

 chloride produces a slight turbidity. Ferrocyanic acid and meta- 

 phosphoric acid do not precipitate, nor does nitric acid even if the 

 solution be saturated with salt. Peptones are Isevo-rotatory ; the 

 rotation has been measured by Siegfried. All albumoses and pep- 

 tones hitherto examined are dissociated by erepsin, according to 

 Cohnheim. 7 



Albumoses and peptones form with acids and with bases salts, 

 the hydrolytic dissociation of which is the same as that of the salts 

 of albumins and the more complex proteids. The chlorides of 

 albumoses have been frequently examined, as they occur during 



1 H. Schrotter, Monatsh.f. Chem. 14. 612 (1893). 



2 M. Siegfried, Zeitschr. f. physiol. Chem. 35. 164 (1902). 



3 F. Miiller, ibid. 38. 265 (1903) ; C. Borkel, ibid. 38. 289 (1903) ; T. Krtiger, 

 ibid. 38. 320 (1903) ; P. Miihle, Amphopepton, Dissertation, Leipzig, 1901. 



4 W. Kiihne, Zeitschr. f. Biol. 29. 320 (1892). 



5 E. P. Pick, Zeitschr. f. physiol. Chem. 24. 246 (1897). 



6 0. Cohnheim and H. Krieger, ibid. 40. 95 (1900). 

 ~ 0. Cohnheim, ibid. 35. 134 (1902). 



