338 ON THE DETERMINATION OF ORGANIC MATTER IN WATER. 
Companies. 
• 
Total solid impurity in 
100,000 parts. 
Organic carbon. 
Nitrogen as nitrates 
and nitrites. 
Ammonia. 
Total combined nitro¬ 
gen. 
Previous sewage con¬ 
tamination estimated. 
Total hardness. 
Chelsea. 
28-28 
•261 
•214 
•004 
•217 
1185 
20 -3 
West Middlesex . . . 
■27-22 
1-020 
•218 
•120 
•421 
2195 
19 4 
Lambeth. 
28-18 
•325 
•220 
•001 
•229 
1305 
20 9 
New River. 
23-12 
•217 
•198 
•001 
•199 
1005 
16-3 
East London .... 
27-22 
•237 
•150 
•002 
•452 
535 
19-7 
As explained at the commencement, organic matters in admixture with water 
undergo slow oxidation ; and when nitrogenous substances are present, the 
nitrogen is converted into nitrous and nitric acids, which, combining with bases 
present, remain as permanent witnesses of the sewage or analogous contamina¬ 
tion to which the water has been subjected. Such “previous organic contami¬ 
nation” may be conveniently expressed in parts of average filtered London 
sewage, which if completely oxidized would yield a like amount of nitrates, 
nitrites, and ammonia. From the analyses of Way, Hofmann, and Witt, 
average filtered London sewage may be assumed to contain 10 parts of com¬ 
bined nitrogen in 100,000. The number so obtained as the “ previous sewage 
contamination ” of a water requires however a correction, since rain-water itself 
contains combined nitrogen as ammonia, nitrate of ammonia, and nitrite of am¬ 
monia. Now the average results of most careful experiments by Messrs. Lawes 
and Gilbert and Professor Way show the presence of -0985 part of combined 
nitrogen in 100.000 parts of rain-water. This corresponds to 985 parts of 
sewage in 100,000 parts of the water. 
Yarious considerations will show that this reduction is abundantly liberal, 
and therefore favourable to the character of the water. The column, therefore, 
headed in the above table “ previous sewage contamination,” is to be understood 
as follows:—Take, for example, the Chelsea water; 100,000 pounds of this 
water has after its descent to the earth as rain been contaminated with 1185 
pounds of average filtered London sewage. But by gradual oxidation conse¬ 
quent upon exposure to the air, the whole of this matter has been transformed 
into harmless inorganic products. The whole of its nitrogen has been converted 
into nitrites and nitrates, and ammonia. Consequently the numbers obtained 
in the seventh column are calculated, by adding together the nitrogen found as 
nitrite and nitrate, and that contained in the ammonia, and subtracting fmm 
the sum the quantity given above as the combined nitrogen contained in 100,000 
pirts of rain-water. In the example selected, 100,000 parts contain "214 of 
nitrogen, under the heading of the fourth column : add to this the quantity 
*003 (about.) of nitrogen contained in the *004 of ammonia, and from the joint 
amount subtract ’0985, the quantity estimated as existing in the same weight of 
rain-water. *214 -f- ’003 — -0985 = *1185, the amount of nitrogen in the 
sewage originally introduced into the water, that is in 1185 parts. 
Addendum. — Nessler's Test for Ammonia. 
Take of Iodide of potassium 2| ounces. 
,, Corrosive sublimate 1 ounce, or q.s. 
„ Solid caustic potash 6 ounces. 
