GENERAL CHEMICAL CHARACTERS OF PROTEINS 51 



N 

 Lacqueur and Sackur added to sodium hydroxide solutions 



the calculated quantities of caseinogen necessary to neutralise it (a 

 solution in which v = 20 was thereby obtained) ; this was diluted to 

 varying concentrations, and the conductivities determined with the 

 following results : 



Per Cent. Caseinogen. v (Dilution). A (Equivalent Conductivity). 

 2-84 40 4 6 '5 



1-42 80 51-3 



0-71 160 56*2 



o-355 320 63-0 



0-1775 640 69-5 



Whence A ~ A * = 0-33. 



-^640 



From this it follows that caseinogen is at least a tetrabasic acid. 



N 

 Now as i gram neutralises 8'8i c.c. sodium hydroxide, its 



equivalent combining weight is =1135. On the assumption 



Oool 



that caseinogen is a tetrabasic acid its molecular weight would be 

 4540, or, on the assumption that it is hexabasic, 6810. 



The sodium salts of caseinogen can, like other protein salts, 

 undergo hydrolysis in solution. The solution of caseinogenate of 

 sodium, which is obtained by just neutralising caseinogen with 

 sodium hydroxide, is slightly opalescent and the opalescence dis- 

 appears on addition of excess of alkali. Furthermore, the point of 

 neutralisation, when litmus is employed as indicator, varies very 

 appreciably with the dilution of the solution. The condition of equi- 

 librium may be represented by the equation 



Kas. nNa + nH 2 O t^ Kas. nH + nNaOH ; 



or possibly acid salts may be formed 



Kas. nNa + mH 2 O 5 Kas (n - m)Na + mNaOH 



(cf. Hardy 1 on serum-globulin). 



The statements with regard to hydrolysis have been confirmed 

 by Lacqueur and Sackur by the measurement of the internal friction 

 of sodium caseinogenate solutions. The magnitude of the internal 

 friction depends chiefly on the concentration of the caseinogen ions ; 

 very small quantities of free acid diminish the friction (thus setting 

 free caseinogen from its salts), whilst correspondingly small quantities 

 of alkali increase it. 



The Salt Formation of Serum- Globulin (Hardy). 



To determine the combining powers of acids and bases with serum- 

 globulin Hardy employed two of the chemical methods (B I. and B 

 II.), viz., direct titration and determination of the amount of globulin 

 (which is insoluble in pure water) soluble in given quantities of acids 

 and bases. 



By the second of the two methods the more accurate results were 

 obtained. Various acids of the concentration O'OO5 N were added 

 to suspensions of globulins containing from 0*28 to 4*1 8 grams in 



1 See p. 53- 



