METHOD OF WILUAMS-WARINGTON 447 



sium bichromate. About half a gram more of the potassium 

 bichromate should be used than is necessary for the oxidation of 

 the substances in solution. The entire oxidation does not con- 

 sume more than from 15 to 30 minutes. 



REDUCTION OF THE ELECTRIC CURRENT 



386. Method of Williams -Warington. This process is appli- 

 cable to solutions or extracts of fertilizers, soils, etc., and rain 

 or drainage waters containing only a small amount of nitrates. 

 From the losses which naturally occur during the evaporation of 

 water, even with all the precautions usually observed, Waring- 

 ton was led to try some method for the determination of nitrates 

 and nitrites in waters without previous concentration. 70 The re- 

 duction of these bodies by the copper-zinc couple formed the 

 basis of these experiments, and they resulted in the following 

 method of manipulation, which is based on a process devised by 

 \Villiams. 71 



The method consists in boiling rapidly one liter of the solution 

 of a fertilizer or rain water in a retort, with a little magnesia 

 previously raised to a low red heat and then washed, until 250 

 cubic centimeters have distilled. The residue is made up to 800 

 cubic centimeters, transferred to a wide-mouthed, stoppered bot- 

 tle supplied with strips of copper and zinc forming electric 

 couples, and set aside, at a temperature of from 21 to 24, for 

 three days. A measured portion of the solution is distilled and 

 the ammonia determined in the distillate by nesslerizing. 



This plan has two advantages : First, the ammonia, as well as 

 the nitrogen as nitrates and nitrites, can be determined in the 

 course of the same operation and in the same sample of the solu- 

 tion. For this purpose it is only necessary to fit the retort to an 

 efficient condenser to remove all ammonia from the apparatus by 

 boiling distilled water in the retort before introducing the solu- 

 tion. The distillate of 250 cubic centimeters obtained as De- 

 scribed above, is well mixed and the ammonia determined in 

 from 25 to 100 cubic centimeters thereof, diluted to 150 cubic 

 centimeters with ammonia-free water. The nitrogen, as nitrates 



70 Journal of the Chemical Society, 1889, 55 : 538. 



71 Journal of the Chemical Society, 1881, 39 : 100. 



