1026 MODIFICATIONS OF PROTEIN. 



when the jar is open, but not when it is covered and access 

 of air prevented. This precipitate is insoluble in the solution of 

 nitre, and possesses the properties of arterial fibrin.* 



PROTEIN. 



Formula : C 40 H 31 N 5 O 12 =Pr (Mulder). When albumen or 

 fibrin is dissolved in a moderately strong solution of caustic 

 potash, and heated to about 120, the small portions of phos- 

 phorus and sulphur which it contains, are separated in the form 

 of phosphate of potash and sulphuret of potassium ; and when 

 this solution is saturated with acetic acid, a gelatinous substance 

 precipitates which is the same from both fibrin and albumen, 

 and constitutes protein. After being washed, protein is still 

 gelatinous, of a greyish colour, and semi-transparent. When 

 dried it is yellowish, hard, easily pulverised, tasteless, insoluble 

 in water and alcohol. Like albumen and fibrin it is not fusible 

 by heat without decomposition. 



Albumen and fibrin may be considered as compounds of 

 protein with sulphur and phosphorus in different propor- 

 tions. Mulder found in fibrin and in the albumen of eggs 

 from 0.36 to 0.38 per cent of free sulphur, with from 0.32 to 

 0.43 per cent of free phosphorus, which quantities of these ele- 

 ments are in the proportion of SPJ. In albumen from the 

 serum of blood, 0.68 per cent of sulphur, and 0.33 per cent of 

 phosphorus were found, or S 2 Pi. The composition of these 

 substances is thus represented by Mulder : 



Fibrin, and the albumen of eggs . . . 10 Pr + S P* 

 Albumen of serum 10 Pr + S 2 P4 



The oxides of lead and silver likewise combine with 10 atoms 

 of protein. The globulin of blood, vegetable albumen, and 

 the casein of milk, treated with alkalies, in the same way as 

 fibrin and albumen, give also a protein which is identical in 

 composition and properties with the foregoing. 



M. Liebig has adopted for protein the formula C 48 H 36 N 6 O 14 , 

 which is different from that of Mulder, although equally com- 



*Sclierer, chemisch-physwlogische Untersuchungen. Annalen der Chemie, &c., 

 X. , October), (1841). 



