418 T. M. Chatard on new Ajialytical Methods. 



In conclusion, there seems to be no doubt that almost any 

 gelatinous jDrecipitate can be successfally treated in this manner. 



§ 3. Tests for Mtrous Acid. 



During the course of some work on the nitrites of nickel and 

 cobalt, it was necessary to have an easy and accurate test for 

 nitrous acid. I therefore reviewed all the tests given for that 

 acid, comparing their relative degrees of delicacy, with tlie fol- 

 lowing results. For testing, a very dilute solution of Fischer's 

 salt, (Co,6N02 + 6(KNO,) + 2Aq), which contained 255V00 

 part by weight of nitrous acid, was employed. 



Schdnbein's* test with a weak solution of indigo decolorized 

 by potassic sulphide failed to give accurate results. Besides 

 there are many substances which would have the same action 

 upon the decolorized indigo as the nitrous acid. 



C D. Braun'sf test with cobaltous chloride and potassic cy- 

 anide gave no reaction with so dilute a solution, even when 

 several cubic centimeters were taken, the reaction only appear- 

 ing when a comparatively strong solution of the nitnte was 



Hadow'sl reaction in which a nitrite when heated with potas- 

 sic ferrocyanide and mercuric chloride forms nitroprussic acid 

 which is detected by an alkaline sulphide, gave good result^ 

 only when the nitrous acid was present in larger quantities, noi 

 being delicate enough to give a reaction with the standard solu- 

 tion of nitrite which I employed. 1 • 1 ti ni 



A modification of this test suggested itself, m which tne^ lu 

 troprussic acid is thus produced. To the solution suspectea 01 

 containing the acid, potassic ferrocyanide and acetic acid a 

 added, and the whole boiled. The solution is allowed to com. 

 and ammonic sulphide added. If nitrous acid was 0|jp°f ^JJ^ 

 present, the characteristic blue reaction will appear. ^^^•^;, 

 the test solution gave the reaction, but it failed with a smaiit 

 quantity. . „rnplv 



The problem was finally solved by another reaction, namt- 

 the production of phenol from aniline by means dmton^ 

 acid. Evaporate the test liquid nearly to dryness, then ru ^^ 

 with a few drops of a strong solution of sulphate ol am^^J''^- ^^ 

 nitrous acid is present the odor of phenol will immeaiate ; 

 suit. This test is remarkably delicate, 1 c. c. of the test soiu 

 giving a perfectly distinct reaction. Nor can nitrous m ^^^ 

 founded with nitric acid, as this last produces no pUeno , ^^ 

 merely a yellow color, which of itself, as is well known, 

 value' as a test for that acid. 



♦ Jahresbericht, 1864, 699. t Ibid- 1865, 702. 



