The Coagulation of Protein by Sunlight. 



243 



rotation is a constant only at the isoelectric point (6). If acid be added, 

 the value for [«] is increased. If alkali be added, the value is temporarily 

 decreased. In order to discover whether this was also a fact with the 

 denatured albumin, two or three drops of HC1 (20 per cent.) were added, so 

 as to adjust the Pn of the solution near to the isoelectric point. The 

 specific rotation rose almost 5° to a constant value of — 87'92° in several 

 hours. The solution was again made alkaline by means of a few droops of 

 ammonia and again the value for the specific rotation fell to — 83 - 0°. The 

 same slow rise to the higher value was observed as in the case of unillu- 

 minated ovalbumin. It is to be noted that the fluctuations from — 83 - 0° to 

 — 89"6° are around a much higher mean value than the one for undenatured 

 material, — 78 - 6°. The significance of this observation is discussed in a later 

 section. Table VI gives the data in detail. 



Table VI.— Optical Rotation of Denatured Serum Albumin. 



Time 

 interval. 



Solution. 



Temperature. 



Ph. 



CIE. 



[«]*■ 





Original 



o 



15 



5-6 



o 



-2 -71 



O 



-78 



•6 





Denatured + NH-. 



14-2 



7-4 



-2-88 



-83 



•3 



1 hour 



+ HCi 



15 



5 -4 



- 3 -01 



-87 



1 



5 hours 





15 



5 "4 



-3 -04 



-87 



•9 



12 hours 





14-5 



5 -4 



-3 -04 



-87 



•9 



5 mins. 



+NH 3 



15 



7-3 



-2-87 



-83 



•o 



j 2 days 



15 



7-3 



-2 -95 



-85 



•3 



3 days 





14 -5 



7-3 



-3-09 



-89 



•4 



1 day 





14-5 



7-6 



-3 -10 



-89 



•6 



1 day 





14 -2 



7-6 



-3-09 



-89 



•4 



Concentration of serum albumin, 3 '46 per cent. 

 Time of previous exposure to sunlight, 2 hours. 



(B) Viscosity and Surface Tension. — A solution of ovalbumin, three times 

 recrystallised and dialysed free from sulphate, was used in the following 

 experiments. Changes in viscosity were measured by an Ostwald viscosi- 

 meter immersed in a thermostat kept at 20° C. and regulated so that the 

 temperature was constant to 0"1° ; 5 c.c. were used for a determination, 

 measured by means of a calibrated pipette. 



The surface tension was measured by means of a Traube stalagmometer 

 (Gerhardt No. Ill), standardised by distilled water and found to give 

 37'10 drops. The instrument was accurate to 0"05 of a drop. It should be 

 pointed out here that in such a measurement the tension measured is between 

 air and the dispersion medium, not between dispersion medium and disperse 

 phase. Any change the latter might undergo, however, would very probably 

 be shown in the former, though not of necessity. 



