On tlie Food of FhvU.s. 
547 
Coal contains nitrogen. When distilled at a red heat for the 
purpose of getting illuminating gas, the greater part of this nitrogen 
unites with hydrogen, and gives rise to ammonia, which is after- 
wards separated more or less completely, and manufactured, 
although frequently in a very wasteful and imperfect manner, into 
ammoniacal salt. Admitting that coal contains i per cent, of 
nitrogen, which can thus be employed (a supposition probably 
not far from the truth), it is easy to see what a prodigious quantity 
of ammonia might be furnished by our coal-gas works, properly 
conducted. 
According to Dr. Ure, in the year 1838 the quantity of coal so 
distilled in London alone amounted to 180,000 tons, containing 
at 1 per cent. 4,0o2,000 lbs. of nitrogen, equivalent to 4,896,000 
lbs. of ammonia ! — the produce of a single city in one year. 
Again, it is a supposition, certainly within the mark, that every 
person, one with another, gives rise to 1 lb. of urine every day, 
containing, according to the estimate of Berzelius, about 210 
grains of urea. Taking the present population of London at two 
millions, this gives 60,000 lbs. of urea dailt/, or 21,900,000 lbs. 
yearly of this valuable substance thuown away — a quantity 
capable of producing by its decomposition 12,410,000 lbs. of am- 
monia. Could one- fourth of this ammonia be converted into flour, 
it would produce the astonishing quantity of 159,687)500 lbs. 
Appendix. 
1. On the Analysis of Soils. 
The exact analysis of a soil, taking into account the precise nature, 
quantity, and state of every ingredient, many of which occur in ex- 
tremely minute quantities, is a chemical problem, perhaps the most 
difScult tliat could be devised, and which the science in its present state 
is hardly competent to solve. 
To give such a mode of approximative analysis as shall be exceed- 
ingly useful, without pretending to fulfil these conditions, is the object 
of the following remarks : — 
The plan described is based on that recommended by Davy, namely, 
the separation of the soil into sand, finely divided matter, and salts, and 
differs principally from those in use by a more careful examination of 
the fine part, which is subjecled to a regular process of mineral analysis. 
The sand and soluble matters are separately examined as usual. 
The sanqile of soil taken from the field with the usual precautions is 
exposed to the air until sensibly dry; in this state a portion is weighed 
out, dried at about 300" Fahr. and the loss of water ascertained. It is 
next carefully elutriated with distilled water, by which the soluble part 
is taken up and the sand and clayey portion sejjarated ; the sand is then 
strongly dried, weighed, and its chemical nature examined. 
