32 



On the Proteid Reaction of Adamkiewicz, §c. 



the proteid reaction abundantly. Preliminary observations that we< 

 have made leave little doubt that this is glyoxylic acid itself. 



If it should prove that the reaction is, as a matter of fact, peculiar 

 to glyoxylic acid, it certainly forms a very delicate test for that 

 substance. 



VI. Glyoxylic Acid Solutions a Practical Test for Proteids. 



By replacing the acetic acid of the Adamkiewicz reaction by weak 

 aqueous solutions of glyoxylic acid a very beautiful and reliable test 

 for proteids is obtained. The colour reaction is brilliant, and the test 

 is, of course, subject to none of the uncertainty inseparable from th& 

 use of acetic acid.* 



In preparing such a test solution, there is usually no need to separate 

 the glyoxylic acid from associated products. Excellent test solutions 

 may be made by oxidising upon the water bath, in the presence of 

 small quantities of ferrous iron, either weak solutions of tartaric acid 

 or mixtures of glycerin and water, great care being taken to ensure 

 that no trace of free peroxide remains at the close of the operation. 

 But we strongly recommend the use of reduced oxalic acid for the pur- 

 pose, as a solution can be prepared with great ease, and almost without 

 regard to conditions. In a moderately strong solution of oxalic acid a 

 few lumps of sodium amalgam are placed, the amount taken of the 

 latter being less than sufficient to neutralise the acid. When the 

 evolution of hydrogen has ceased, the solution is jjoured off from the 

 mercury and filtered. It will be found, even after large dilution, to 

 yield an intense reaction with proteids if used instead of acetic acid 

 under the familiar conditions of the Adamkiewicz test. The proteid, 

 or the proteid solution to be tested, should be first added to the 

 reagent, and then strong sulphuric acid poured down the side of the 

 test-tube. The reaction may be first observed at the junction of the 

 fluids and the latter subsequently mixed. At least one-third volume 

 of sulphuric acid should he used, but the quantity may be almost 

 indefinitely increased. There is no tendency to charring. 



* It is certainly rare to find a specimen of acetic acid which, vields no reaction, 

 though many contain too little glyoxylic acid to give a satisfactory colour. It 

 seems to be possible, however, that there have been cases of a proteid derivative 

 being found to yield no Adamkiewicz reaction, in which the negative result was 

 really due to the acetic acid employed. We have, for instance, prepared and 

 carefully purified the primary albumoses from Witte's peptone by the method of 

 E. P. Pick (' Zeitsch. f. physiol. Chem.,' 1899, vol. 28, p. 219). Unlike this observer, 

 we have found these products to yield a marked Adamkiewicz reaction ; and with 

 all reserve, we venture to suggest that the acetic acid employed by Pick at this, 

 stage of his observations may have chanced to be free from chromogenic power. 



