17S 



l)i'raliir('s cxlciuliiin' t'roin lo -180°, on tlic ijliysical (miii- 

 stants of colloidal solulioiis of a laru'o inimbor of siib- 

 staiic'cs, such as, zymase, (\u<»' al])umiii, uclaliiic, ii,iim 

 ai'al)ic, saponin, mclacliolcstcrin, myosin, sodium olcalc, 

 casein, polyaci\\lic acid and its esters, j)oly\-iiiyl alcoliol, 

 etc. In geiier<d, dilute solutions (0,001 lo l.OV' ) of these 

 sul)stances exhibited, aftei' liaviui^' ])een frozen and thawed, 

 liii»her diffusion coefficient, interferometer value, viscosity, 

 catai)lioretic mii'i-ation velocity, specific conductivity and 

 also an increased absorption of snch ii,ases as ethylene and 

 acetylene. More concent lated solutions (2'/) showed, 

 after freezing and thawing, lower values of these constants 

 than did the nnfi'ozen controls. The authoi-s conclude 

 that, in dilute solutions, freezing effects a disaggregation 

 of the individual particles, whereas, at higher concentra- 

 tions, it i)i'oduces an aggregation of these primary 

 particles. 



In a study of the surface tension of frozen and thawed 

 egg albumin and gelatin solutions, Nord (1934) found that 

 this property increases with the duration of freezing but 

 not with its repetition nor with the exposure to very low 

 temperatures. 



Heller (1934) studied coagulation by freezing in sols of 

 FeCL, Fe(NO.O* and FeOOH, in terms of hydrogen-ion 

 concentration, of duration of dialysis and of the length of the 

 time of exposure to low temperatures. He found : 1. That 

 coagulation never occurred when the pH was lower than 

 6.1; 2. That a dialysis of 69 days induced coagulation in 

 a case in which a dialysis of 3 days was ineffective ; 3. That 

 the length of time the material was maintained in the 

 congealed state, often increased the degree of coagulation. 

 Comparing these results Avith those obtained in coagula- 

 tion by stirring and noticing similar conditions in the two 

 cases, he concluded that coagulation by freezing must re- 

 sult from a fusion of the colloidal particles under the com- 

 pression exerted by ice. In freezing, as in stirring, 

 coagulation would be possible only when the '* double 

 laver" at the surface of the micelles is weakened; such a 



