HEAT, LIGHT AND PRESSURE 309 



shaken just as the first traces of heat coagulation appear the 

 incipient coagula will again pass into solution. The apparent 

 irreversibility of the later stages of heat-coagulation is probably 

 attributable to the high internal friction of the floccula which 

 are formed, leading to extremely slow molecular movement and 

 the introduction of a time-element of very considerable magnitude. 



This deduction receives decided support from the discovery 

 by Chick and Martin (18) (19) (20) that the heat-coagulation of 

 proteins consists of two processes which they severally term 

 " denaturation " and ''agglutination." In acid solutions the 

 process of agglutination or aggregation takes place at a rate 

 very greatly in excess of denaturation and therefore the rate of 

 formation of flocculated protein is primarily determined by the 

 rate of denaturation, i.e., by the slower process. In alkaline 

 solutions, however, aggregation does not occur, but may be 

 induced by subsequent acidification or by saturation with sodium 

 chloride. In acid solutions the rate of denaturation is acceler- 

 ated by H+ ions and these decrease during the reaction through 

 the binding of acid by the denatured protein. If the concen- 

 tration of H+ ions be kept constant the reaction follows the 

 monomolecular reaction-formula, but if this precaution be omit- 

 ted then the reaction velocity falls off more quickly than would 

 be anticipated from the monomolecular formula (18) (100). 

 Similarly in alkaline solutions of egg-albumin the OH' ion con- 

 centration decreases during denaturation, but if the OH' concen- 

 tration be kept constant the reaction is of the first order. 



The diminution in the acidity of acid solutions of protein 

 during heat-coagulation has also been observed and quanti- 

 tatively determined by Sorensen and Jurgensen (97) and Quagli- 

 ariello (79). 



We may conclude, therefore, that the results of Chick and 

 Martin are in satisfactory harmony with the view of Hofmeister 

 and Pauli that coagulation, including the heat-coagulation of 

 protein, is essentially a phenomenon of dehydration of which 

 the first stage, that of internal neutralization through the loss 

 of the elements of water from end — NH2 and — COOH groups, 

 probably corresponds to the phenomenon of "denaturation" 

 while the subsequent or simultaneous polymerization of these 

 anhydrides leads to the formation of particles so large as to 

 assume the properties of matter in mass, i.e., floccuH. 



