December 29, 1922] 



SCIENCE 



733 



various cc. of 0.1 N acid. These ec. of 0.1 

 N acid in 100 ce. solution are the ordinates of 

 the curves in Fig. 1. The abscisses are the pn 

 to Avhich the protein solution was brought by 

 the addition of acid. It takes always exactly 

 three times as many ce. of 0.1 N H3PO4 as it 

 takes oc. of 0.1 N HCl or H2SO4 to bring 

 1 gm. of isoelectric albumin in 100 cc. solution 

 to the same pjj. In order to bring the 1 per 

 cent, solution of originally isoelectric albumin 

 to Ph 3.2, 5 ec. of 0.1 N HOI or H2SO4 and 

 15 cc. of 0.1 N II3PO4 must Ibe contained in 

 100 cc. of the solution. To ibring the albumin 

 to Ph 3.4, 4 cc. of 0.1 N HCl or H2SO4 and 

 12 cc. of 0.1 N H3PO4 must be contained in 

 the solution, and so on. 



Oxalic acid is, according to Hildebrand, a 

 monobasic acid at a pjj of 3.0 or below, but 

 begins to split off the second 'hydrogen ion in 

 increasing proportion above pn 3.0. The titra- 

 tion curves show that about t^vic« as many cc. 

 of 0.1 N oxalic acid as 0.1 N HOI are required 

 to bring the 1 per cent, solution of isoelectric 

 albumim to the same p^ 'below 3.0; while it 

 takes less than twice as many ce. of 0.1 N 

 oxalic acid as 0.1 N HCl to bring the albumin 

 solution to the same pjj if the pjj is above 3.0. 



It can be shown in the same way with the 

 aid of titration curves that isoelectric albumin 

 com'bines with alkalies in the same stoichiomet- 

 rieal way as any acid, e. g., acetic acid, would 

 combine Avith the same alkalies. If the cc. of 

 0.1 N KOH, NaOH, Ca(0H)2, or Ba(0H)'2 

 in 100 cc. solution required to bring a 1 per 

 cent, solution of isoelectric protein to the same 

 Ph are plotted as ordinates over the pn of the 

 protein solution as abscissfe, it is found that 

 the values for all four alkalies fall on one 

 curve as they sbould if the combination oc- 

 curred strictly stoichiometrically. 



The same stoichiometrieal results were ob- 

 tained also with casein and gelatin by the 

 v/riter, and with edestin and serum globulin 

 by Hitchcock. There is little doubt that they 

 Avill be obtained in the case of all proteins. It 

 follows from this that proteins react with acids 

 and alkalies in the same way as do amphoteric 

 crystalloids like amino-acids. If the methods 

 for measuring the hydrogen ion concentrations 



of protein solutions had been employed by the 

 colloid chemists nobody would have thoug'ht of 

 suggesting that proteins react with acids and 

 alkalies according to the empirical adsorption 

 foi-mula of Freundlich instead of stoichiomet- 

 rically. 



The purely chemical character of the com- 

 bination of proteins with hydrochloric acid can 

 also be demonstrated by measuring the chlorine 

 ion concentration of the 'solutions of protein 

 chloride. When HOI is added to NH3 (accord- 

 ing to Werner) the H ions of the HCl are at- 

 tracted to the nitrogen of the ammonia, while 

 the 01 ions remain unaltered. The same type of 

 reaction occurs when HOI is added to a solution 

 of isoelectric gelatin. This was proven by 

 measurements of the pc, of solutions of 

 gelatin chloride. Different ec. of 0.1 N HCl 

 were contained in 100 c«. of 1 per cent, solu- 

 tions of originally isoelectric gelatin and the Ph 

 and Pc, of the solutions were measured, the 

 Pj, with the hydrogen electrode and the p 

 with the calomel electrode. ' It was found 

 that the p^^ was the same as if no gelatin had 

 been pi-esent while the pn was, of course, 

 higher; thus showing that part of the hydro- 

 gen combines with the NH2 and NH groups of 

 the protein molecule while the 0! remains free 

 (Table I). Dr. Hitchcock has obtained sim- 

 ilar results with crystalline &gg albumin, 

 edestin, casein, and serum globulin, by using a 

 silver chloride electrode, so that it is possible 

 to state that these results are true for most if 

 not all 'proteins. 



TABLE I 



