18 



ainido-acids, and with a sample of globulin among the proteids a crys- 

 talline residue separated out in the flask on cooling. This residue was 

 not examined further than to determine qualitatively that it contained 

 nitrogen. The proportion borne by the nitrogen left in such fixed 

 residual products to that collected as gas evidently varied with the 

 conditions of the particular experiment, as well as with the nature of 

 the substance acted on. 



All the proteids and analogous materials treated gave some gaseous 

 nitrogen. For the most part the amount was about two-fifths of the 

 whole amount present; but occasionally a larger proportion, as in one 

 experiment with globulin just about one-half, and in another with 

 myosin about three fourths. In this last case the action was allowed 

 to go on at a high temperature for a time much longer than usual. 

 The remarks already made in regard to the simpler amidic substances, 

 as to modification of results by variation of the conditions of experi- 

 ments, fully apply also to the experiments with proteids and their 

 congeners. The lack of sharpness of ending to the reaction was more 

 noticeable with the latter class of materials than with the former. 



Although these experiments with alkaline hypobromite were interest- 

 ing, and occasionally offered points which might repay further investi- 

 gation, they did not, taken altogether, afford any satisfactory basis for 

 distinguishing in analysis between the classes of materials to be studied 

 in contrast with each other. 



BEHAVIOR WITH CUPRIC HYDROXID (STUTZER'S REAGENT). 



The formation of insoluble compounds of the proteids with cupric 

 hydroxid, while leaving the simpler amids soluble in the presence of an 

 excess of this reagent, has been extensively adopted as the means of 

 separation, but experiments made in this way have not given the writer 

 much confidence in the method as a general one. In some cases, working 

 with a proteid alone, the copper compound underwent partial solution, 

 a blue liquid being formed, although care had been taken to avoid the 

 presence of free alkali. Possibly this result was due to incipient 

 decomposition of the proteid material. As Stutzer himself has pointed 

 out, peptones are very incompletely precipitated by cupric hydroxid. 

 A further objection is to be found in the very slight solubility of the 

 copper salts of some of the simpler amido-acids, especially leucin and 

 glutamic acid; in a less degree the same statement applies to aspartic 

 acid. Even at the temperature of boiling water the copper compounds 

 of these substances are but very sparingly soluble, and if the liquid, 

 after digestion with cupric hydroxid, be filtered cold, 1 the compounds 

 in question will, if present, be almost certainly left on the filter along 

 with the proteid material. 



'As directed by the Association of Official Agricultural Chemists, Bulletin No. 46 

 of the U. S. Department of Agriculture, Division of Chemistry (1895), p. 25. 



