'240 



Mr. E. G. Young. 



The precipitate obtained was soluble in alkali but insoluble in excess 

 water or acid. The amount was small, and only a low fraction of the total 

 protein in solution. 



Experiment 2. — The Influence of Ph Variation on the Light Beaction. 

 To determine the possible effect of Ph variations, a series of tests were 

 prepared containing ovalbumin solution of the third crystallisation product, 

 to which a few drops of acetic acid of 10 per cent, strength had been added. 

 A control tube containing the same albumin solution, with buffer mixture, 

 was illuminated at the same time. Further controls of tests 1 and 5 were 

 prepared, and kept at the same temperature in the dark. The proportions 

 and results are recorded in Table III. 



Table III. — Effect of Ph Variations on Unbuffered Ovalbumin Solutions. 



Test. 



Mixture. 



Ph. 



Eesult. 



1 



5 c.c. 



solution + 2 c.c. buffer solution 



4-8 



+ 



2 



5 c.c. 



„ +0"05 c.c. acetic acid 



4 7 





3 



5 c.c. 



„ +0-10 c.c. „ 



4-6 





4 



5 c.c. 





4-45 





5 



5 c.c. 



„ +0-20 c.c. p 



4 2 





Time of exposure to sunlight, 8 hours. 



Concentration of ovalbumin, approximately 2 per cent. 



The Ph values were determined at the close of the experiment, and the 

 results were only seen in reality when the tubes were all brought to the 

 isoelectric point of ovalbumin. On neutralising the acidic solutions with 

 dilute NaOH, a marked precipitate appeared, about Pu 5*0 (4"8-5 - 4), which 

 was soluble in excess of alkali, but reprecipitated at the same Pn on adding 

 acid. This precipitate remained undissolved on further acidification of the 

 solution. The volume of the precipitate varied directly with the original 

 degree of acidity. The two unilluminated control tubes showed no pre- 

 cipitate whatever when adjusted to a Ph of 5 - 0. This experiment shows 

 that acid increases the rate of the light reaction, but that in solutions very 

 low in their concentration of electrolytes, the albumin is not precipitated. 

 This observation brings the reaction in very close similarity to heat coagula- 

 tion. The absence of a precipitate in the unbuffered solutions of Experi- 

 ment 1 can now be explained, in the light of the fact brought out by 

 Experiment 2. 



A wider range of Ph variations was next tried, with the purpose of 

 discovering the influence of alkali on the reaction. Phosphate a»d phthalate 



