328 CARNEGIE INSTITUTION OF WASHINGTON. 



(6) The Melting-Point of Benzene, and the Effect of Common Impurities. 



This investigation was a continuation of previous work (see Year 

 Books No. 13, p. 352, and No. 16, p. 300). A yet more careful study of 

 the melting-point of pure benzene was made with the help of Dr. W. C. 

 Schumb. The value 5.494° was found as the mean of many observa- 

 tions on several samples of benzene, using two thermometers stand- 

 ardized in Paris at the International Bureau of Weights and Measures. 

 It was found that when saturated with water, benzene freezes at a 

 point 0.095° lower than when free from water. Hence, in order to 

 obtain an exact value for the freezing point of the pure material, less 

 than 1 per cent of the saturation amount of water must be present. 

 The effect of dissolved air, also, was studied. 



(7) Study of Concentrated Thallium Amalgams. 



With the help of Mr. C. P. Smyth, the study of concentrated thai- 

 hum amalgams (begun with Dr. Wilson and Dr. Daniels) was con- 

 tinued. Further evidence concerning the behavior and constitution of 

 amalgams containing less than 20 per cent of mercury was obtained, 

 pointing to a reasonable explanation for the difference between the 

 electrode potential of pure electrolytic thallium and amalgamated 

 thallium. This investigation was not quite finished and will be con- 

 tinued in the autumn. 



Several previous researches were brought to the point of publica- 

 tion and their titles will be found listed in the bibhography. 



Sherman, H. C, Columbia University, New York, N. Y. Chemical Investi- 

 gation of amylases and related enzymes. (For previous reports see Year 

 Books Nos. 11-17.) 



The work of the year has consisted chiefly in the continuation of the 

 investigations referred to in our last report and the beginning of a 

 somewhat extended study of the effects of amino acids upon the 

 enzymic hydrolysis of starch by different amylases, both in natural and 

 in purified form. 



A paper embodying the results of experiments completed last 

 autumn on the influence of hydrogen-ion concentration upon the 

 enzymic activity of three typical amylases was read before the Society 

 for Experimental Biology and Medicine and published in the Journal 

 of the American Chemical Society for February 1919. 



The work on the action of amylases and digestive secretions upon 

 starches of different origin, preliminary results of which were outhned 

 in our last report, has been completed and published (Journal of the 

 American Chemical Society, July 1919). Wheat, maize, and rice 

 starches, similarly purified, showed equal digestibility or rate of 

 enzymic hydrolysis. This was true whether the enzyme employed was 

 saliva, commercial pancreatin, purified pancreatic amylase, malt 

 extract, purified malt amylase, commercial taka-diastase, or the 

 purified amylase of Aspergillus oryzce. With all of these, potato starch 



