THE COMBINATION OF GELATIN WITH HYDROCHLORIC 



ACID. 



By DAVID I. HITCHCOCK. 



{From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, May 12, 1922.) 



Titration curves for gelatin with different acids have been obtained 

 by Loeb,^-- and used to show that the protein reacts stoichiometrically 

 with the different acids. The amount of a strong acid combined 

 with the protein may be obtained from the titration curve (in which 

 the abscissae are pH values and the ordinates concentrations of acid) 

 by subtracting from the ordinates the amounts of acid necessary to 

 bring the same volume of water, without protein, to the same pH 

 values. In this way Loeb^ obtained a curve for the amount of HCl 

 combined with 1 gm. of gelatin at different pH values. Similar 

 curves were obtained by Tague^ for the combination of amino-acids 

 with NaOH, and by the writer^ for the combination of edestin with 

 acids. Each of these combination curves appeared to become 

 horizontal beyond a certain pH; i.e., after enough acid (or alkali, in 

 the case of Tague's experiments) had been added, the amount com- 

 bined with the ampholyte became constant. 



In a recent paper by Lloyd and Mayes" a curve is given to represent 



the amount of HCl combined with 1 gm. of gelatin. This curve, 



however, does not become horizontal, but rises with increasing acidity 



in a rather discontinuous manner. These authors did not obtain the 



amount of combined HCl in the way just described, but calculated 



[H+] corr. ^, 



It by the formula n' = n where [H+] corr. = VIH"*"] X[C1-], 



a 



» Loeb, J., /. Gen. Physiol., 1920-21, iii, 100. 



* Loeb, J., Proteins and the theory of colloidal behavior, New York and London, 

 1922. 50-51. 



»Tague. E. L., /. Am. Clicm. .Soc, 1920. .xlii, 173. 

 « Hitchcock, D. I.. J. Gen. Physiol., 1921-22. iv, 597. 



» Lloyd, D. J., and Mayes, C, Proc. Roy. Soc, London, Scrii-s B, 1922, .\ciii, 69. 



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