18 PROTEIDS. 



changed to a lilac colour by acids but not by salts which have an acid reaction to 

 litmus. The second is turned to bright carmine by free alkalis but not by 

 salts which have an alkaline reaction to litmus. 



It is however on the whole more probable 1 that acid- and alkali- 

 albumin are distinct, though very closely allied substances, and we 

 might go even so far as to say that probably every proteid yields 

 its own kind of either the one or the other proteid on treatment 

 with acids and alkalis. But as yet we do not possess any means 

 of distinguishing between the several forms of each substance by 

 any ordinary reactions. 



The chief though somewhat unsatisfactory evidence which is ad- 

 vanced as to the difference of the two products is the following. 



1. Alkali-albumin is in general more soluble than acid-albumin. 



2. When precipitated by neutralisation the former (alkali) is 

 flocculent, the latter (acid) is more viscid, transparent and gelatinous. 



3. When dissolved in a minimum of alkali and heated to 100 in 

 sealed tubes, alkali-albumin coagulates, acid-albumin does not. 



4. When alkali-albumin is dissolved in Na 2 HP0 4 it is not precipi- 

 tated on the addition of an acid until all the salt has been converted 

 into NaH 2 P0 4 2 . (Of. above p. 16.) 



5. Acid-albumin can be converted into alkali -albumin by the 

 action of strong alkalis, but the reverse conversion of the product thus 

 obtained or of an ordinarily prepared alkali-albumin into acid-albumin 

 is stated to be impossible. 



The rotatory power of alkali-albumin varies according to its source ; 

 thus when prepared by strong caustic potash from serum-albumin, the 

 rotation rises from - 56 (that of serum albumin) to - 86, for. yellow 

 light. Similarly prepared from egg-albumin, it rises from 38 '5 to 

 -47, and if from coagulated white of egg, it rises to -58-8. Hence 

 the existence of various forms of alkali-albumin is probable. 



The substance 'protein,' described by Mulder 3 appears, if it exists 

 at all, to be closely connected with this body. All subsequent observers 

 have however failed to confirm his views, and it is only mentioned here 

 from its historical interest. Since Mulder's time the name has been 

 applied to various forms of proteid. 



Preparation. The best method is that originally introduced by 



1 Morner, Pfliiger's Arch. Bd. xvn. (1878), S. 468. But see also Kieseritzky, 

 Inaug.-Diss., Dorpat, 1882. Abstr. in Maly's Jahresber. Bd. xn. (1882), S. 6, and 

 Kosenberg, Inaug.-Diss., Dorpat, 1883. Abstr. in Maly, Bd. xm. (1883), S. 19. 



2 Soyka and Morner, loc. cit. See also Soxhlet, Jn. f. prakt. Chem. N. F. Bd. 

 vi. (1872), S. 1. 



3 Ann. d. Ch. u. Pharm. Bd. xxvm. (1838), S. 81. 



