Economy of Nitrogen. 
153 
1878.] 
they should, the entire fertilising ingredients excreted by 
the inmates of the cottage, they consist chiefly of an impo- 
tent residuum. To call this a restoration to the soil of 
what has been taken from it is mere mockery. Not one- 
haif the compounds withdrawn from our fields and gardens 
for the food of man, whether in town or country, are ever 
returned to where they belong. 
So far, however, we have dealt merely with the waste of 
the fertilising matter in human excreta ; but there is also 
the case of our domestic animals. When cattle and sheep 
are pasturing, and when horses are working in the fields, 
not only their dung, but their urine is deposited upon the 
soil. Under most other circumstances, however, the latter, 
which is the more valuable of the two, goes to swell the 
waste we have already mentioned. In the towns it is con- 
veyed into the sewers, and in the country it escapes into 
ditches, adding thus no inconsiderable item to our yearly 
loss of combined nitrogen. 
The remarks which we made on the waste of nitrogenous 
matters by the processes of putrefadfion or fermentation 
going on in cesspools admit of a more extended application. 
Let us take the case of ordinary town-sewage. We can 
calculate with tolerable exactness how much nitrogen it 
ought to contain per gallon, if we know the gross number 
of the population and the total volume of the sewage. The 
figure thus obtained will, however, fall below the exadt 
truth, since the proportion of nitrogen entering the sewers 
will be increased by the excretions of domestic animals and 
by the washings of slaughter-houses, &c. Yet if we take a 
gallon of the sewage, and submit it to adtual analysis with 
the utmost care, we shall obtain a result very much short 
of the calculated percentage ; some 20 to 50 per cent of the 
combined nitrogen, more or less according to circumstances, 
has escaped. In what form this loss takes place can 
scarcely be doubted. Were it given off as ammonia it 
could easily be detedted ; but ammonia does not readily 
evaporate from such dilute solutions, and at such low tem- 
peratures. We conclude, therefore, in accord with two 
chemists who have made the analysis of waters their spe- 
ciality, and who on most points differ very widely in opinion, 
that the loss takes place in the form of free nitrogen. This 
we shall find to be the case whenever vegetable or animal 
matter containing nitrogen passes into a state of fermenta- 
tion. A part of such nitrogen reappears as ammonia, and 
may be arrested by the aid of absorbents and of certain 
