EXPERIMENTAL DATA OF GAS- INTERCHANGE DETERMINATIONS. 



In all of these experiments the lettered series were made in 1912, those 

 with numbers in 1913. In any one series the same letter or figure indicates 

 that the same material was used, the individual members of the series being 

 shown by an index figure or letter. 



TABLE 53. Temperature and gas-interchange. 



The material used was all mature and fairly turgid joints of Opuntia versicolor. It had 

 been sent from Tucson, Arizona, and kept for some weeks in the laboratory in New York at 

 a temperature of from 20 to 22 C. and under conditions which prevented any considerable 

 drying. The material was a mixed lot, and various determinations of the acidity showed 

 the value of 1 c.c. pure juice to be from 0.9 to 1.10 c.c. N /10 alkali. Under the conditions 

 at which it was kept the acidity remained fairly constant. During actual experimentation 

 it was not kept long enough at the extremes of temperature to greatly affect the acidity, 

 though there was the usual tendency for the amount of acid to increase at the lower tem- 

 perature and to decrease at the higher. The material was respectively cooled or warmed 

 for from 2 to 3 hours before the corresponding determination was made. At other times it 

 was at ordinary room temperature of 20 to 22 C. Determinations were made in New 

 York during April 1912. 



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