WATEE 21 



In order to perceive the colour formed by Nessler's test, 

 look through a certain depth of the fluid placed over a 

 ■white surface ; an inch or so in a test-tube is sufficient, 

 the least yellow tint can then be detected at once. It is of 

 supreme importance in applying this test that the test-tube 

 be perfectly clean and free from ammonia. 



Oxidizable Matter. — The presence of organic matter in 

 water not necessarily nitrogenous, may be determined by 

 the use of an agent which by yielding up its oxygen oxidizes 

 the organic matter which may be present. The test by 

 itself is not a very satisfactory one, as there are bodies 

 in water other than organic which have an affinity for 

 oxygen. 



To the solution under examination add a trace of 

 dilute acid, and then boil for twenty minutes with a 

 solution of gold chloride. If organic matter be present 

 the yellow colour turns to pink, violet, olive, or even a 

 black precipitate, depending on the amount of organic 

 matter present ; the usual colour is violet more or less 

 deep. This test is of no use in the presence of nitrous 

 acid. 



The darkening of the silver chloride obtained by the 

 chlorine test should also be noted ; where organic matter is 

 present it rapidly darkens. For the purpose of comparison 

 a dilute solution of salt and water may be employed. A 

 weak solution of permanganate of potassium may also be 

 used, one grain to four ounces of water. A few drops of 

 this should be added to the water under examination, 

 sufficient to give it a delicate pink colour. If much 

 organic matter is present the colour soon goes, varying 

 from a few minutes to an hour. If two drops of the 

 above solution be added to two ounces of water, the pink 

 colour should remain for at least one and a half hours if 

 the water be good. Unfortunately there are other sub- 

 stances in water besides organic matter which reduce 

 permanganate, the test is only useful in conjunction with 



others. 

 Phosphoric Ackl.—Tme water contains no phosphates ; 



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