Chemical Analysis of Potable Waters. 211 



Pollution Commission of Great Britain in the examination of a large 

 number of waters. The process consists in the evaporation of a stated 

 quantity of the water which has been freed from all the carbon and 

 nitrogen which existed in it in an inorganic form, excepting in ammo- 

 nia, by treatment with a saturated solution of sulphurous acid, by 

 which the nitrates and nitrites are reduced with the expulsion of 

 their nitrogen and the carbonates decomposed with liberation of their 

 carbonic acid. Nitrogen in ammonia is fixed and has to be deducted 

 in the final computation. The residue obtained is then submitted to 

 organic analysis, resulting in the conversion of the carbon into carbonic 

 acid and the liberation of the nitrogen as such. The mixture of gases 

 is then subjected to volumetric gas-analysis and the results .finally 

 reported as parts of "organic carbon" and "organic nitrogen in 

 100,000 of water. The relative proportion of nitrogen to carbon is 

 supposed to throw light upon the nature of the organic matter origi- 

 nally present, since in animal substances the ratio is higher than in 

 vegetable. Frankland finds that the ratio of nitrogen to carbon is for 

 upland surface waters, on an average, 1 to 10; for water fro- culti- 

 vated land, 1 to 6; for shallow wells, 1 to 4; for sewage, 1 to 2. It 

 has been found, however, that the effect of oxidation upon peaty mat- 

 ninish the proportion of carbon, while during the oxida- 



nimal matter it is the nitrogen ^ 



tich diminishes most rap- 



idly. Therefore the proportions of nitrogen to carbon ur vegetable and 

 animal matter vary in opposite directions during oxidation, a fact 

 which greatly adds to the difficulty of decidmg as to the natnreof the 

 '^^ZETLorj, the most scientific and accurate of an, 

 ever proposed, bnt it is exceedingly difficult, requiring costly and 

 elaborate apparatus and especial skill on the part of the operator 

 Mallet says, "It is better adapted to regular use in the analysis of 

 many samples of water in a large public laboratory than to occasmnal 

 use by a private individual in now and then examining a sample of 

 water." For these reasons, chiefly, it has not come into 

 and in this country it has been employed by but very few , *«u£ 

 Objections on the score of difficulty, however, should not be allowed 

 to weigh against the process itself if it is of value, but on this point 

 much difference of opinion exist,. As migh be supposed Wanklyn 

 and Tidy condemn it, and while most chemists admit tha the princi- 

 ple is a good one, it is pretty generally believed that * 

 by uo means as reliable as they are claimed to be b, the originator of 

 the process. Mallet, after summing up its errors and the objectmn, to 

 it, says : " The combustion process, in its present f orm cannot be con- 

 sidered as 'determining' the carbon and nitrogen of the organic mat- 



