156 
Economy of Nitrogen. 
[April, 
formed and worked. To make these, earth was collected 
together from the sides and bottoms of cesspools, drains, 
urinals, and dunghills. It was mixed with plaster from old 
walls, and stratified with decaying animal and vegetable 
refuse. These beds or heaps were sheltered as far as pos- 
sible from cold and rain, and were sometimes watered with 
urine. In course of time a whitish efflorescence began to 
appear in different parts of the heap. The earth was then 
dug up, lixiviated with hot water, and the solution thus ob- 
tained on concentration yielded crystals of saltpetre. Now 
it is evident that all the substances of which these nitre- 
beds were formed were in themselves nitrogenous, and 
capable of being used as manures. What was sold as salt- 
petre was simply so much robbed from the farm and the 
garden. As to the composition of the soil taken from the 
foundations of cesspools, stables, cow-houses, dunghills, &c., 
there can be now no doubt. Even the ground all about 
ordinary dwelling-houses was in former days saturated with 
excrementitious matter. We have adopted another form of 
waste ; what our forefathers allowed to soak into the earth 
beneath and around their houses we run into the streams 
and seas. Our method may be a little more favourable to 
health, but it is waste all the same. The great fadh that the 
saltpetre thus obtained from the nitre-beds was merely a 
transformation of the combined nitrogen put in them in 
various organic compounds was formerly not perceived. 
The nitre-bed was supposed, in some unexplained manner, 
to have the power of fascinating that chainless wanderer 
the free nitrogen of the atmosphere, and chaining him down 
as a slave to do man’s work. Had, however, the constituents 
of the heap been accurately analysed, — a requirement ut- 
terly impossible when nitre-beds first came into use, — it 
would have been found that the nitrogen in the saltpetre 
obtained, instead of being more than equivalent to the 
nitrogen originally present, invariably fell short of it, and 
that a portion consequently of this element made its escape 
in the uncombined gaseous state. To this subjedh we shall 
be compelled to revert more fully below. 
The Indian saltpetre, which till lately formed the bulk of 
our supply in England, was also obtained by the lixiviation 
of soils, which contained it as saline crusts. It was not, 
however, any and every soil which could be made use of, 
but such only as had become saturated with nitrogenous 
matter capable of yielding nitric acid by oxidation. The 
importation of saltpetre from India, therefore, was a robbery 
