FACTORS INFLUENCING DIASTASE FORMATION 225 



The vapor tension method 



The vapor tension above a salt solution of dilute concentration 

 held at a constant temperature is definite and constant. It is 

 possible by changing the temperature of a solution of given den- 

 sity to raise or lower the vapor tension above the solution. By 

 changing the density of the solution and maintaining a constant 

 temperature, it is possible to obtain a wide range in vapor tension. 



Half-gallon fruit jars were used as containers in each case. The 

 tops were supplied on the inside with a hook for suspending the 

 wire containers described below. The jars were supplied with 

 solutions as follows: 



(1) 400 cc. saturated solution of CaCl 2 . Twadell reading 75.7° 



(2) 200 cc. saturated solution of CaCl. plus 200 cc. of distilled 



water. Twadell reading 40 . 0° 



(3) 100 cc. saturated solution of CaCl 2 plus 300 cc. of distilled 



water. Twadell reading 20.5 



(4) 50 cc. saturated solution of CaCl 2 plus 350 cc. of distilled 



water. Twadell reading 9.0° 



(5) 400 cc. of water. Twadell reading 1.1 



3 







For literature regarding the derivation of Twadell readings 

 see Martin (1915), Sadtler (1912) and Thorp (1917). 



After the jars were sealed they were placed into large tem- 

 perature cases for 24 hours before the wire containers containing 

 the barley were placed into them. By this means, there was set 

 up a series of jars whose moisture content varied from the lowest 

 to the highest possible under the prevailing temperature. Five 

 series were thus maintained at temperature as follows: 5°C, 

 10°C, 15°C, 20°C, and 25°C. 



After the jars had remained in the cases a sufficient length of 

 time for the solutions and the air above them to reach an equilib- 

 rium, the jars were furnished with the wire baskets containing 

 50 grams of barley each. The cylindrical baskets were made of 

 wire netting of fine mesh and were suspended by a bail from a 

 hook in the top of the jar. The lower end of these baskets was 

 5 cm. above the liquid. Each container was weighed several 

 times a day until it attained a constant weight. 



