454 



SCIENCE 



[N. S. Vol. LII. No. 1350 



quired in the case of HNO3 or HCl; while 

 twice as many c.c. of 0.1 N oxalic as of HZNOg 

 should be required. On the other hand, it 

 should require just as many c.c. of 0.1 N 

 HjSO^ as HlSrOj Fig. 1 shows -that this is 

 the case. The ordinates of this figure are the 

 c.c. of 0.1 N acid required to bring 1 gm. of 

 isoelectric gelatin to the pH indicated in the 

 abscissae by the four acids mentioned, namely 

 HNOg, HjSO^, oxalic and phosphoric acids. 

 The curves for HjSO^ and HNOg are iden- 

 tical while, for the same pH, the value for 

 HjPO^ is always approximately three times 

 and the value for oxalic acid is always ap- 

 proximately twice as high as for HNO3. 



On the basis of the same reasoning as ap- 

 plied to acids we should expect that equal 

 numbers of c.c. of 0.1 K" GaCOH), and 

 Ba(0H)2 as of LiOH, NaOH, and "KOH 

 should be required to bring 100 c.c. of a 1 per 

 cent, solution of isoelectric gelatin to the 

 same pH and the writer was able to show 

 that this is the case. Similar results were 

 obtained with crystalline egg albumin. 



When we have a solution of a gelatin-acid 

 salt of originally 1 per cent, isoelectric gelatin 

 and of a certain pH, e. g., 3.0, we have free 

 acid in the solution and a certain amount of 

 the anion of the acid in combination with 

 gelatin. We can find out by volimietric 

 analysis how much of the anion is in com- 

 bination with the protein by making certain 

 corrections discussed in former papers. In 

 this way it can also be ascertained that all 

 weak dibasic acids combine in molecular pro- 

 portions with isoelectric protein, while strong 

 dibasic acids and diacidic alkalies combine 

 in equivalent proportions with proteins, as 

 is shown by Table I. It follows from this 

 table that for the same pH the amount of 

 HNO,, oxalic, and phosphoric acids in com- 



C.c. of 0.01 N Acid in Combination with 10 c.c. of 

 a 1 Per Cent. Gelatin Solution at Different pE 



HNO3 ...14.35 4.1 

 Oxalicacid 9.6 j 8.75 

 H3PO4...I 112.4 



3.5 3.7 3.0 4.1 4. 



2.85 2.45 1.9*1.45 

 6.00 4.3 3.0I 

 9.00 7.4 5.8'4.5 



0.75 

 2.1 



bination with the same quantity of originally 

 isoelectric gelatin is always in the proportion, 

 of 1:2:3. 



We can therefore state that the ratios in 

 which ions combine with proteins are iden- 

 tical with the ratios in which the same ions 

 combine with crystalloids. Or in other words, 

 the forces by which gelatin and egg albumin 

 (and probably proteins in general) combine 

 with acids or alkalies are the purely chemical 

 forces of primary valency. 



The most important fact for our purpose is 

 that from the combining ratios just men- 

 tioned the influence of acids and bases on the 

 physical properties of proteins can be pre- 

 dicted. This influence is altogether different 

 from that stated in the so-called Hofmeister 

 series of ions or by the ion series of Pauli and 

 his collaborators, and this difference is due to 

 the fact that these latter authors compared 

 the effects of equal quantities of acids or 

 alkalies while we found it necessary to com- 

 pare the physical properties of solutions of 

 proteins of the same hydrogen ion concentra- 

 tion. If this is done the following rule is 

 found. All those acids whose anion combines 

 as a monovalent ion raise the osmotic pres- 

 sure, viscosity, swelling of protein about 

 twice as much as the acids whose anion com- 

 bines as a bivalent anion for the same pH. 

 The same valency rule holds for the cations 

 of different alkalies. 



We have seen that at the same pH three 

 times as many c.c. of 0.1 N HjPO^ as of 

 HNO3 are in combination with 1 gm. of origi- 

 nally isoelectric gelatin in 100 c.c. of solution. 

 It follows from this that the anion of gelatin 

 phosphate is the monovalent ion HjPO^ and 

 not the trivalent anion PO^. It follows like- 

 wise from the combining ratios discussed that 

 the anion of oxalic acid in combination with 

 protein is the monovalent anion HCjO^. The 

 same is true for all weak dibasic or tribasio 

 acids, namely that they combine with pro- 

 teins forming protein salts with monovalent 

 anion. It follows also from the combining 



