The Coagulation of Protein by Sunlight. 



239 



Ph. 



3- 1—4-4 



4- 4—6-0 

 64—7-8 



Indicator. 

 Methyl orange. 

 Methyl red. 

 Neutral red. 



To obviate possible errors due to the presence of proteins and salts, the 

 method of dilution was adopted. Thus 1 c.c. of fluid was pipetted into a test 

 tube, 4 c.c. of CC>2-free water added, and a suitable quantity of the indicator. 

 A comparator was employed in cases of turbidity or foreign coloration. The 

 procedure of dilution was tested and the values obtained by the use of the 

 indicators were verified electrometrically on test solutions. 



Eesults. 



Experiment 1. — Susceptibility of different Crystallisations to Light Change. 



A series of test tubes were prepared containing solutions of the first three 

 crystallisations of ovalbumin. These were approximately of 2 per cent, 

 strength and had been dialysed free from electrolytes. They were adjusted 

 to the same Pn by addition of a few drops of N/10 HC1. Another series was 

 prepared containing 1 c.c. of the different ovalbumin solutions and 2 c.c. of a 

 buffer mixture, made up of equal volumes of N/1 CH 3 COOH and N/1 

 CH 3 COONa, giving a P H of 4"74. The results are shown in Table II. 



Table II. — Susceptibility of Different Crystallisations to Illumination. 



Test. 



Mixture. 



Ph. 



Result. 



1 



3 e.c. s 



olution, 1st crystallisation 







5-4 







1 c.c. 





+ 2 c.c. 



buffer... 



4-6 





2 



3 c.c. 



" 2nd " 







5 -4 







1 c.c. 





4 2 c.c. 



buffer... 



4-7 





3 



3 c.c. 



", 3rd 







5 -4 







1 c.c. 





+ 2 c.c. 



buffer... 



4 7 



+ + 



Time of exposure to sunlight, 6 hours. 



Albumin concentration of unbuffered solutions, 2 per cent. 



From the results recorded in Table II, where precipitates appeared in the 

 buffered solutions of the second and third crystallisations of ovalbumin, it 

 became evident that repeated crystallisation tended to render. the albumin 

 more sensitive to light. It is to be noted that no precipitate appeared in 

 the unbuffered solutions. Now, between the unbuffered and buffered 

 solutions there existed three differences. The buffered solutions possessed 

 a slightly lower concentration of protein, a slightly higher concentration of 

 hydrogen ions, and a much greater electrolyte-content than the unbuffered 

 solutions. 



