112 



PHYSIOLOGICAL CHEMISTRY. 



is so opaque that, when placed before the slit of the spectroscope in a 

 layer of one centimetre, it completely extinguishes everything but the 



FIG. 17. 



SPECTRUM OF PETTENKOFER'S TEST, with the Biliary Salts in watery solution. 



red ; and yet it may be diluted with water without showing any turbidity 

 or losing its color. A solution of the above strength is amply sufficient 

 to exhibit Pettenkofer's reaction as well as its spectroscopic characters. 

 If a solution of the biliary salts should prove, when treated by Petten- 

 kofer's test, too opaque for spectroscopic examination, another portion 

 may be reduced, before applying the test, to about the strength of one 

 part to 500. When a strongly colored purple fluid has been rendered 

 turbid and decolorized, as above described, by the addition of water, its 

 transparency and color may be again restored by the addition of sul- 

 phuric acid ; but this method is less convenient than the former. 



If Pettenkofer's test be applied to the biliary salts in alcoholic solu- 

 tion, its spectrum contains two absorption bands instead of one. The 

 first is situated at E, and is identical with that in a watery solution of 

 the same salts. The second band, at F, is usually rather narrower and 

 fainter than the first, although sometimes the two are of equal intensity. 



The pink or purplish-red fluid, produced by Pettenkofer's test with a 

 watery solution of either codeine or morphine, has a spectrum some- 

 what similar to that of the biliary salts. If the ruddy color of the fluid 

 be strongly pronounced, its spectrum, even in a layer of one centimetre, 

 is very short, terminating about midway between D and E, or even 

 before that point, showing the red and yellow clear and bright, but very 

 little of the green. If diluted with water, the mixture is not rendered 

 turbid, but its color is reduced, being soon changed to a faint amber, or 

 often to a light apple-green, w^hile the former peculiarities of the spec- 

 trum disappear. The best way is to place the fluid before the slit of 

 the spectroscope in a layer of two centimetres before its ruddy hue is 

 fully developed, and while it is still of a light pink. The color then 

 gradually becomes more pronounced, and, when it has attained the 

 proper strength, the spectrum exhibits a certain, though ill-defined 

 absorption band at E. Beyond the band, the spectrum is very dim, 

 terminating gradually between F and G. 



The distinction between the spectrum of Pettenkofer's test with 

 biliary salts and that with the opium alkaloids is, that in the former 



