5GG 
UTILISATION or SEWAGE. 
It may even be said that it is in reality the manufacture of 
artificial manure, which gives to sewerage its peculiar value and 
icnportance for the purposes of husbandry, and it is this 
which 1 shall endeavour to explain in what follows. 
It is well known that the manufacture of artificial manure 
is based on the doctrine that the nourishment of all culti¬ 
vated plants consists of inorganic or mineral substances. 
Manure consisting of organic substances can be produced by 
the agriculturists only. The farmer produces farmyard 
manure; the manufacturer, on the other hand, mineral 
manure, with which he furnishes the farmer with those effi¬ 
cient elements wanting in stable dung. The most important 
fabrication is that of superphosphate of lime. The question 
of immediate importance to be decided is the value to the 
farmer of the sewerage used, and it is easy to find this by 
comparing sewage matter wdth guano, the effect and price 
of which are known to the farmer, and whose value he is 
able to judge. The problem to be solved is, therefore, how 
much of the efficient elements of guano a farmer can convey 
to his field in a ton of sewage; or how many gallons of sewer 
water are equivalent to a cwt. of guano. Regarding the 
component parts of the best sorts of guano, we have certain 
and reliable data—those relating to sewer water are less so; 
but we might long ago have been fully informed of its 
average contents if, last year, at the mouth of each sewer in 
London, five gallons of water had been collected morning 
and evening every day during the week, and at the end of 
the seventh day one gallon of the collected seventy gallons 
subjected to chemical analysis. It would be necessary, of 
course, to determine as nearly as possible the quantity of 
water discharged at each sewer. The learned baron then 
gives Professor Way^s analysis of sewer water in London, 
from which it appears that 101 tons (20,200 gallons) of sewer 
water contains the same amount of phosphoric acid, more 
than three times as much as ammonia, and sixteen times as 
much potash, as one cwt. of the best Peruvian guano. It 
will be observed (adds Baron Liebig) that there is a great 
ditference in the proportion of phosphoric acid to ammonia 
in guano and sewer water. In guano this proportion is 6 
parts of phosphoric acid to 8.^ parts of ammonia ; in sewer 
water this proportion is 6 parts of phosphoric acid to 26 
parts of ammonia. The reason of this disproportion in the 
amount of phos{)horic acid and ammonia in sewer water is at 
once perceived if we remember that the bones of the slaugh¬ 
tered animals do not find their way into the sewers. These 
bones are, however, the manuring matter in which phos- 
