CRYSTALLIZABLE NITROGENOUS MATTERS. 113 



case the absorption band at E is very distinct, and often quite black, 

 when viewed in a layer of two centimetres' thickness; while in the 



FIG. 18. 



SPECTRUM OF PETTEXKOFER'S TEST, with the Biliary Salts in alcoholic solution. 



latter it is always dim and ill-defined. With the biliary salts, also, the 

 fluid may often be diluted with its own or even twice its volume of 

 water, and the absorption band still remain visible ; but with morphine 

 or codeine a very moderate dilution destroys the character of the spec- 

 trum and causes the absorption band to disappear. 



The violet-colored fluid produced by Pettenkofer's test with albumen 

 has a well-marked and peculiar spectrum, easily distinguishable from 

 that of the biliary salts. If too opaque for spectroscopic examination, 

 it may be diluted with water and afterward cleared up by the further 

 addition of sulphuric acid. It then shows a single absorption band, 

 extending from somewhere about the line E to the line F. In con- 



FIG. 19. 



SPECTRUM OF PETTENKOFER'S TEST, with albumen. 



centrated solutions it may begin considerably to the left of E, and 

 extend thence to F. In those which are more dilute, it may reach 

 only from a little beyond E to F. It is, therefore, always limited on 

 the right by the line F, extending farther toward E and D, according 

 to the degree of concentration of the liquid. Its edges are never very 

 well defined, but are more distinct when the band is narrow than when 

 it is wide. Beyond the band, the refrangible portion of the spectrum 

 is quite dim. 



7. Creatine, C 4 H 9 N 3 (X, from xpeas, flesh. 



This is a neutral crystallizable substance, which exists in the mus- 



H 



