1919] AGRICULTUKAL CHEMISTRY — AGROTECHNY. 203 



The H-ion concentrations of all the vegetable juices were in the neighborhood 

 of pH 6 witli the exception of tomato juice, which was about pH 4. However, 

 in bringing the H-ion concentration of tlie juices to various values between 

 pH 2 and 12 less acid and more all^ali were required for the dehydrated prod- 

 ucts than for the fresh vegetables for tlie same concentration^ This difference 

 was more marljed with air-dehydrated than with vacuum-dehydrated products. 

 This is thought to indicate definite changes brought about in dehydration, 

 probably in the character of the protein material. 



The enzym reactions of all the vegetable juices studied were destroyed by 

 boiling for several minutes. The oxidase reaction with carrot, yellow and 

 white turnip, and potato juices was greatly increased on dilution. No well 

 defined H-ion concentration for maximum action with oxidase, peroxidase, 

 and catalase was observed although the actions were better in the more 

 allialine solutions between pH 7 and 10. They were inhibited in acid solution, 

 pH 2 and 3 for oxidase and peroxidase and pH 4 for catalase, except in the 

 case of the tomato. With the exception of cabbage and carrot, the enzym 

 action was less in the juice from the dehydrated than from the fresh vegetables, 

 and less in the air-dehydrated than in the vacuum-dehydrated products. 



The optimum amylase action in cabbage, carrot, and white turnip juices was 

 at about pH 6, and in yellow turnip juices at from pH 4 to 7. The optimum 

 H-ion concentration for the vegetable juice amylases coincided with the 

 natural H-ion concentrations of these juices. 



In considering the enzym results, the authors point out that the state of 

 ripeness and the age of the vegetable undoubtedly influence the activities. In 

 regard to debydration, the shorter the period of time in wliieh heat is applied 

 the smaller will be the changes in enzym action, which probably accounts 

 partly at least for the smaller changes in the vacuum dehydration products. 

 It is suggested that the dark color of unboiled air-dehydrated potatoes may 

 be avoided by increasing the H-ion concentration of 10"° or 10"' N to 10"^ N 

 before dehydration, thus equalizing the H-ion concentration of the potato and 

 ordinary water. This may be accomplished by treating the potatoes with dilute 

 acid solution before dehydration. 



Oxidizing enzyms. — I, The nature of the "peroxid" naturally associated 

 with certain direct oxidizing' systems in plants, M. W.. Onslow {Biochem. 

 Jour., 13 (1919), No. 1, pp. 1-9). — Evidence is presented to show that in plants 

 in general which brown on injury the peroxidase is associated with an 

 aromatic substance giving the reaction characteristic of the catechol grouping. 

 In such plants the peroxidase on injury activates the oxidation of the 

 aromatic substances, giving rise to peroxids, and the system peroxid-peroxidase 

 will then blue guaiacum. Plants which do not brown on injury do not contain 

 a substance with the catechol gi'ouping, and their enzyms do not catalyse the 

 oxidation of substances with such a grouping. 



Observations on the accuracy of different methods of measuring small 

 volumes of fluid, F. W. Andeewes (Biochem. Jour., 13 (1919), No. 1, pp. 37- 

 .'/.'(). — The author reports a comparison of the accuracy of the pipette and drop 

 methods of measuring sera, particularly in the preparation of a series of 

 doubling dilutions. 



The chief conclusions from the observations made are (1) that volumes of 1 cc. 

 and 0.5 cc. can be measured by pipette with reasonable accuracy, but that 

 the error resulting from the attempt to deliver 0.1 cc. may amount to 5 per 

 cent even when a 0.1 cc. pipette is employed; (2) that the only way in which 

 accurate results can be obtained with a pipette in preparing an ascending 

 series of dilvitions is to use it as a delivery pipette and wash and dry it between 



