15 ® 
Economy of Nitrogen. 
[April, 
accessible store of phosphoric acid on the face of the globe, 
and consequently the total quantity of wheat and of beef 
that can be produced and the number of human beings that 
can be maintained, is lessened by every gallon of sewage we 
pour into a tidal river or into the sea. To put the fa eft in 
another light : every stroke of the costly and ornate 
pumping-engines at Barking Creek and at Crossness is 
destroying potential life, or rendering existence more diffi- 
cult throughout the world ! Surely this is an outcome of 
engineering skill on which the nineteenth century has small 
cause for self-congratulation. 
It is indeed true that the phosphoric acid thus so bounti- 
fully poured into the sea may be, in the lapse of years, 
recovered in the shape of fish, serviceable for food or for 
manure ; but this is a long, a tedious, and a doubtful circu- 
lation. If the excreta of men and animals are placed upon 
arable soil, their valuable constituents are rapidly made 
available and assimilated by plants, and may re-appear 
witbin a twelvemonth in the shape of food ; but if poured 
into the sea their phosphoric acid, &c., will probably be first 
absorbed by low organisms, animal or vegetable. These 
will sooner or later become the food of fishes, and the 
matter in question may thus ultimately become available 
for human support. 
In one case indeed we may, on the present system, receive 
back sewage matters much sooner than we wish. The par- 
ticles of solids cast into the sea “ hug the shore,” just as 
corks floating in a basin of water keep to the side, and there 
are swallowed by those “ scavengers of ocean,” shrimps. 
Thus they may happen to be re-eaten by man even before 
assimilation. A chemist of the present day, who occasion- 
ally writes on sanitary topics from an original and indepen- 
dent point of view, remarks that thus — 
“ Even-handed justice 
Commends the poisoned chalice to our lips.” 
A still more glaring example of waste occurs in the case 
of nitrogen, an element having important analogies with 
phosphorus, rivalling the latter in its relations to organic 
— and especially to animal — life, and playing a far more im- 
portant and more varied part in the arts and manufactures. 
Manifold in appearance as are the methods in which this 
king of the elements is wasted, they may, with few excep- 
tions, be reduced to one. To understand this great mode of 
waste we must glance at the two almost contradictory 
aspeCts which nitrogen is capable of assuming. On the one 
