CRYSTALLIZABLE NITROGENOUS MATTERS. Ill 



point. For that purpose, the test-tube may be cooled by occasionally 

 immersing it in cold water. Thirdly, the addition of sulphuric acid 

 should be made slowly, and should be stopped as soon as a red tint 

 begins to show^ itself, the mixture being left at rest until the violet 

 and purple colors are developed. 



There are various other substances which yield a red, violet, or 

 purple color, when treated with sugar and sulphuric acid. Among 

 these are oleiue, oleic acid, ethereal oil, amyl-alcohol, albuminous 

 matters, and the salts of morphine and codeine. Albumen of the 

 blood, white of egg, and the opium alkaloids in the proportion of ten 

 parts per thousand, if treated with Pettenkofer's test, all produce a 

 color undistinguishable from that obtained with the biliary salts. 

 These substances, however, with the exception of morphine; may all 

 be excluded by previously treating the fluid as above described ; namely, 

 evaporating to dryness, extracting with alcohol, precipitating with ether, 

 and dissolving the precipitate in water. The salts of morphine might 

 still remain, as they are soluble both in water and in alcohol, and may 

 be precipitated by ether from their alcoholic solution. This substance, 

 however, is very unlikely to be present in an extract of the animal 

 fluids, especially in the proportion of ten parts per thousand. 



Pettenkofer's test is a very delicate one. A watery solution of pure 

 sodium glycocholate, made in the proportion of one part to 2,000, yields, 

 at the end of fifteen minutes, a clear violet-pink color, if the test be 

 applied with care ; and a solution of sodium taurocholate, in the pro- 

 portion of one part to 3,000, will give a similar color at the end of an 

 hour. The characters of the test are the same in both cases, as the 

 reaction is really produced by cholic acid, derived from the decomposi- 

 tion of either of the biliary salts. 



The spectrum of Pettenkofer's test may be of service in distinguish- 

 ing it from similar reactions produced by other organic substances. If 

 either or both of the biliary salts, dissolved in water, be treated with 

 sugar and sulphuric acid until a violet or purple color is produced, and 

 the colored fluid then placed before the slit of the spectroscope, its 

 spectrum shows a wide and dark absorption band at E, extending from 

 midway between D and E to a quarter part the distance between E 

 and F, the central parts of the band being darker than the edges. 

 Beyond the absorption band, the spectrum is dim, fading gradually, 

 and terminating somewhere about the line G. 



When the purple color produced by Pettenkofer's test with the biliary 

 salts is very pronounced, the fluid is usually too opaque for spectro- 

 scopic examination, even in a layer of one centimetre ; and if diluted 

 with water, its purple color disappears, and it becomes turbid, owing 

 to re-precipitation of the cholic acid. This difficulty may be obviated by 

 making the solution of biliary salts sufficiently dilute in the first instance. 

 A solution of sodium glycocholate, in the proportion of one part to 500, 

 treated with Pettenkofer's test, gives in a few moments a clear violet- 

 pink color, which afterward becomes a rich purple. The purple fluid 



