19 



RELATIONS TO ALCOHOL AS A SOLVENT. 



It lias been repeatedly proposed to use strong alcohol for the precip- 

 itation of the proteids, with a view to tlieir quantitative determination, 

 and this even in cases involving the simultaneous presence of some of 

 the ainidic compounds under discussion, such as the flesh bases. 1 But 

 not only do the character and amount of the proteids so precipitated 

 or left insoluble vary with the strength of the alcohol and the quantity 

 of it used, but the further serious objection presents itself that nearly 

 all the simpler amids and ainido acids are either insoluble in alcohol or 

 so slightly soluble that it is practically impossible to wash them out 

 satisfactorily from the precipitated or coagulated proteids. A method 

 which is not properly applicable to such important substances as 

 asparagin among vegetable food materials, and kreatin among those 

 of animal origin, manifestly deserves but little consideration. 



BEHAVIOR WITH SEVERAL NEW OR LITTLE USED REAGENTS. 



A number of miscellaneous experiments were tried with reagents 

 which have either been but occasionally applied to materials of the 

 kind under examination, or have not been so applied at all, so far as 

 published records show. 



A weak solution of pure phenol (carbolic acid), trichloracetic acid, 

 formic aldehyde in aqueous solution, and hydrazoic acid (azoiniide) 

 were thus tried, but from none of these reagents were results obtained 

 which furnished any ground for a general method of distinguishing 

 the two classes of nitrogenous materials which were being studied. 



BEHAVIOR WITH PHOSPIIO-TUNGSTIC ACID. 



This reagent, the discussion of which I have left to the last, has 

 proved of much more value than any other I have tried, and its appli- 

 cation under proper conditions affords, I believe, a fairly satisfactory 

 practical solution of the question I have undertaken to examine. The 

 use of phospho-tungstic acid for the precipitation in general of nitrog- 

 enous compounds, alkaloidal, ainidic, and proteid, is, of course, well 

 known and often practiced, but some of the special facts on which may 

 be founded its application to the purpose now under discussion are 

 believed to be new, and the particular use made of these points of 

 behavior has not been before described. In connection with the experi- 

 ments made with phospho-tungstic acid, the results obtainable from a 

 parallel series of experiments with a strong solution of tannic acid were 

 compared, one of these two reagents being found under special circum- 

 stances to replace the other with advantage. 



The precipitant was employed not as a sodium or other salt, but as 

 the phospho-duodeci-tungstic acid, crystallized in small cubes and dis 



!See Watts's Dictionary of Chemistry, revised edition. Vol. IV, p. 330, and H W 

 Wiley's Principles and Practice of Agricultural Analysis, Vol. Ill, p. 453. 



