10 PROTEIDS. 



pension in water. They are also obtained by the prolonged action of 

 alcohol in excess upon members of Classes I., III. and IV. Their 

 solubilities, except in solutions of neutral salts, are in general similar 

 to, but less than those of Class IV. 



CLASS VI. Albumoses and peptones^. 



The true peptones are extremely soluble in water. They are not 

 precipitated by acids, alkalis, neutral salts or many of the reagents 

 which precipitate other proteids. They are precipitated but not 

 coagulated by even the prolonged action of alcohol. Peptones are 

 readily diffusible, albumoses less so. Some of the albumoses are 

 readily soluble in water, some are less soluble. They are distinguished 

 from peptones by being precipitated when their solutions are saturated 

 with neutral ammonium sulphate. They yield precipitates with many 

 of the reagents which precipitate other proteids, and it is specially 

 characteristic that the precipitates they yield with nitric acid and with 

 ferrocyanide of potassium in presence of acetic acid disappear when 

 warmed and reappear on cooling. 



CLASS VII. Lardacein or amyloid substance. 



Insoluble in water, dilute acids and alkalis and saline solutions. 

 Converted into members of Class II. by strong acids and alkalis. 



THE CHEMISTRY OF THE SEVERAL PROTEIDS 2 . 



CLASS I. Native Albumins. 

 1. Egg-albumin. 



As obtained in the solid form by evaporating its solutions to dryness 

 at 40, preferably in vacuo. it forms a semi-transparent, brittle mass, of 

 a pale yellow colour, tasteless and inodorous. Dissolved in water it 

 yields a clear neutral colourless solution. This solution coagulates on 

 heating, but the temperature at which the coagulation takes place varies 

 considerably with the concentration and is largely dependent upon the 

 presence or absence of salts. The more commonly observed temperature 

 is 7073, but Gautier states 3 that coagula may also be obtained at 54 

 and 63. The more dilute the solution is the higher is the temperature 

 at which it coagulates, thus finally resembling a solution of albumin 



1 The albumoses are classed with the peptones partly from their close relation- 

 ship to these substances and partly for convenience. 



2 In addition to the works already quoted consult Beilstein, Hdbch. d. org. Chern. 

 Ed. in. (1889), Sn. 1258-1310, for all data concerning the proteids. 



3 Chimie appliquee d la Physiol. &c. T. i. (1874), p. 242. Haycraft and Duggan, 

 Proc. Roy. Soc. Edinb. 1889, p. 364. Starke (Swedish). See Abst in Maly's 

 Jahresbericht, xi. (1881), S. 19. 



