TECHNIQUE OF ELECTROCHEMICAL MEASUREMENTS 461 



vanometer is rendered easier and a less sensitive galvanometer 

 can be employed than would otherwise be required. It should not 

 be forgotten, however, that although a small concentration of KCl, 

 for example, does not alter the dissociation of caseinates of the alka- 

 lies nor the combining-capacity of casein for bases (Chap. VIII) 

 yet this is certainly not the case with many other proteins. 



In this connection it is to be carefully noted that if the solution 

 employed to dissolve the casein be top alkaline, little or nothing is 

 gained by the rapidity of its solution, because the rapidity of its 

 hydrolysis is also great. On the other hand, as I have said, if too 

 small a proportion of free alkali is present solution is so slow that 

 hydrolysis is extensive. Evidently an avoidance of both of these 

 extremes will yield the most satisfactory results. I have found 

 the proportion 10 cc. of N/IO KOH to 1 gram of casein to be the 

 most satisfactory solvent for this protein. In the experiments 

 described in Chaps. IX and X, save in the formation of solutions 

 containing more than 100 X 10~^ equivalents of base per gram of 

 casein, therefore, the procedure was as follows: Part of the KOH 

 was neutralized until the portion unneutralized stood in this pro- 

 portion to the mass of casein undergoing solution, the casein was 

 dissolved therein, and then the desired final proportion of KOH to 

 casein was attained by the further addition of HCl. For example, 

 it was desired to obtain a solution of 1 per cent casein in 0.005 

 N KOH. Accordingly, to 75 cc. of 0.1 iV KOH were added 50 cc. 

 of 0.1 iV HCl and in this were dissolved 2.5 grams of casein; upon 

 the attainment of complete solution and while stirring, 12.5 cc. of 

 0.1 AT" HCl were added and the whole solution was made up to 250 

 cc. with distilled water; another solution was made up in precisely 

 the same way but without the introduction of the casein; the 

 conductivities of both solutions were than determined and their 

 difference (= X) estimated.* The two solutions were arranged in 

 the gas-chain in the manner described above and the potential 

 between the gas-electrodes immersed in them determined. Hence, 

 of course, the OH' concentration of the solution not containing 

 casein being known, that of the solution containing casein was 



* Since the concentration of KCl is the same in both solutions it adds the 

 same amount to both conductivities and this disappears in their difference; 

 that is, presuming that the caseinate does not combine with or decompose the 

 KCl and that the presence of excess of K+ ions does not depress the dissociation 

 of the potassium caseinate; Cf. Chap. VIII. 



