VITAMIN A 233 



bubble through the liquid during the heating process at the rate of about 

 one bubble per second. At the end of 4 hours the flask was cooled with 

 running water and the tomato juice then removed to an evacuated bottle. 

 Both the unheated and heated samples were stored in a refrigerator. 

 When portions were removed for the feeding tests the amount with- 

 drawn was displaced by nitrogen. 



With the samples obtained under rigorous precautions for excluding 

 atmospheric oxygen, it was found that 7.0 cubic centimeters of heated 

 juice daily were required to produce the same gain in weight as 5.8 cubic 

 centimeters of unheated juice daily. Thus, with the greatest care taken 

 to exclude oxygen from the system in which the vitamin was heated, 

 about 17 per cent of the vitamin A was destroyed in 4 hours heating at 

 97° C. ± 2°, at the natural acidity of the tomato juice; viz., about 

 pH 4.2. 



To determine the effect of heating the vitamin in the presence of 

 oxygen, experiments were undertaken in which the tomato juice was 

 heated on a steam bath under a reflux condenser for 4 hours at 97° C. 

 ± 2° with air aspirated through the sample at the rate of about one 

 bubble per second throughout the heating. The animals receiving 7.0 

 cubic centimeters of this heated juice daily made approximately the 

 same growth as the animals receiving the 5.8 cubic centimeters of the 

 unheated juice daily. Thus no measurable difference in destruction of 

 vitamin A was found between the experiments in which the vitamin was 

 heated in the strict absence of oxygen and those in which oxygen was 

 present abundantly throughout the period of heating. 



Evidently vitamin A in the form in which it exists in this primary 

 (vegetable) source is less susceptible to oxidation than had generally 

 been supposed in recent years in view of the experiments upon heating 

 and aerating animal fats, as outlined above. 



As it had been found that vitamin B in tomato juice is more rapidly 

 destroyed if the acidity of the medium is decreased or if the juice is 

 made faintly alkaline, experiments were made to determine whether a 

 similar change of hydrogen-ion activity (pH) would increase the de- 

 struction of vitamin A as it exists in tomato juice. 



The portion to be subjected to the heat treatment under changed 

 hydrogen-ion activity was brought to the desired pH of 9.2. The juice 

 thus prepared was heated in parallel with juice of natural acidity (ap- 

 proximately pH 4.2) on a steam bath for 4 hours at 98° C. ± 2° under 

 an atmosphere of nitrogen as already described. The juice in the two 

 flasks was then quickly cooled and, to the sample whose pH had been 

 changed, hydrochloric acid was added in amount just sufficient to 



