NOTE ON T H E LIQUEFACTION O F GELATIN BY SALTS BY T. R. BRIGGS AND EVELYN M. C. HIEBER
It is a well-known fact that both the velocity with which aqueous gelatin solidifies on cooling and the temperature at . which the jelly forms are influenced by the presence of dissolved substances.1 Alkali sulphates, citrates, tartrates and acetates, as well as glycerin, raise the temperature of gelatinization, while chlorides, bromides, iodides and sulphocyanates lower it, the iodides and sulphocyanates being most active. The following simple experiments serve well to illustrate the phenomenon and they also show that the salts are without permanent effect upon the gelatin. We are unaware of any one having established the latter point experimentally, though Larguier des Bancels hints of having done SO.^ Commercial gelatin of the highest grade was submitted to long-continued dialysis to remove soluble impurities. Mixtures of gelatin, salt and water were prepared, each containing approximately 5 percent of gelatin. The mixtures were placed in test tubes in a constant temperature bath a t 19’ C and allowed to stand 36 hours. The data follow:
TABLEI Condition of Gelatin a t I 9 ’ C Added Electrolyte
Concentration of Salt
ZnCls 33% KCl 33 NH~NO, 33 KSCN 33 MgClz 33 Saturated (cold) KN03 Saturated (cold) NHgCl
After 30 minutes
After 24 hours
After 36 hours
Fluid Jelly Fluid Fluid Fluid Fluid Fluid
Fluid Jelly . Fluid Fluid Jelly Semi-fluid Jelly
Fluid Jelly E’luid Fluid Jelly Semi-fluid Jelly
Cf. Pascheles: Pfluger’s Archiv., 71,333 (1898); Steele: Zeit. phys. Chem., 40, 689 (1902); Levites: Zeit. Kolloidchemie, 2, 162 (1908);Sadikoff: Zeit. phys. Chem., 41, 15 (1904). 2
Larguier des Bancels: Comptes rendus, 140,290 (1908).
Note on the Liquefaction of Gelatin by Salts
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The contents of the test tubes were then transferred to dialyzing thimbles of collodion. After 24 hours! dialysis at 19' C, the mixtures in all the thimbles were found t o have set to a firm jelly.. The experiments show that removal of ZnClz, NH4N03, KSCN or K N 0 3 permits the gelatin to reassume its normal power of gelatinization. The three thimbles, containing the solidified gelatin from the experiments with ZnClz, NH4N03and KSCN, were next placed in solutions of ZnC12, NH4N03and KSCN (33 percentj, respectively. After one hour the contents of each thimble were seen again to be completely fluid, showing that the process of liquefaction and gelatinization produced by salts is entirely reversible, bein'g similar in this respect to liquefaction and gelatinization due to changes of temperature. Cornell University
