248 



Pennington — A CJiemico- Physiological 



acid, and finally with distilled water until the washings 

 did not react with silver nitrate. It was then dried in the 

 air, and was preserved for use in tightly-stoppered glass 

 bottles. 



A preparation of diastase was obtained from Messrs. 

 Bullock & Crenshaw, Philadelphia. This was found to be 

 only partially soluble in water, yielding when filtered a 

 clear liquid of a pale straw yellow. 



The starch paste, made by pouring starch, mixed with 

 cold water, into boiling water, contained i gram in ioocc. 

 It was freshly prepared each day. The strength of the 

 diastatic solution soon changed, hence it was necessary 

 to prepare this daily. 



The tests were made by placing the beaker containing 

 the starch and diastase in a white bowl, and covering 

 with a colored screen. These bowls, when a temper- 

 ature of 45 to 50 C. was desired, were partially filled 

 with heated water. The progress of the reaction was 

 noted by removing from time to time a drop of the liquid, 

 and applying the iodine test. The control experiments 

 under white light were conducted in like manner, except 

 that the glass screens contained only distilled water. The 

 work was done in direct sunlight. As it was found that 

 the light intensity caused a very material variation in the 

 time required for this hydration, the experiments were 

 made only on very bright days, and then only in the mid- 

 dle of the day when the sun's rays were most direct. 

 Diastase solutions of varying strength were used, though 

 if too dilute the end reaction was hard to determine. 



The experiments were carried on from the middle of 

 February to the end of April. 



For the six screens the following ratios were found, the 

 time in white light being taken as unity : 



White 1. 00 



Darkness 1.28 



Violet 2.00 



Blue 1. 21 



Green 1.14 



Yellow 0.76 



Orange 0.85 



Red 1. 00 



