462 Abstract Report of Agricultural Discussions. 
Meeting of WeehJy Council, May 2Sth. Lord Walsingham, Vice- 
President, in the Chair. 
Lecture on Town Sewage. 
Dr. Voelcker said : It has been calculated that nearly 200,000,000 
tons of liquid pass annually thi-ough the London sewers, containing 
an enormous quantity of excremcntitious matters, of which the 
substances have been very carefully calculated both for the London 
sewers and also for other towns. I desire especially to refer to the 
excellent paper published some time ago by Mr. Lawes in the 
* Society of Arts J ournal,' which seems to me very conclusive. Mr. 
Lawes states, that the total amount of such matter, when deprived 
entirely of water, comes to 4G lbs. per head per annum, in which 
there are 35 lbs. of organic, and 11 lbs. of mineral substances. 
The principal, if not the sole, valuable fertilising matter in the 
organic substance is the nitrogen, which is found, partly as 
ammonia, or ammoniacal salts (chietly carbonate of ammonia), and 
partly, to a minor extent, in the shape of organic matter in a state 
of incipient decomposition, in which state it readily contributes to 
fertility. The most valuable part of the mineral matter in the 
ashes is phosphoric acid, phosphate of lime, and potash, which 
enter into the composition of the urine. The nitrogen is by 
far the most valuable element of sewage. IMr. Lawes calculates 
the total quantity of nitrogen in the London sewage at 88o9i tons, 
which corresponds to 10,758j tons of ammonia; and the total 
amount of excrement itious matter, when perfectly dried, at 51,286|- 
tons. We can thus arrive pretty well at a theoretical notion of 
tlie value of the sewage both of London and of other towns, and 
likewise,pf the average composition of sewage. 
But the actual analyses of samples, taken at various times, 
perhaps alford us a still better criterion. Many of these have been 
published in Dr. Hoffman and Mr. Witt's report to the govern- 
ment ; others in Mr. Mechi's pamphlet on the sewage of towns, as 
it atfects British agriculture ; the most recent analyses of London 
sewage, perhaps, are those which have been made by Dr. Letheby 
for the City of London. Taking the average of Dr. Letheby's 
analyses, I find that the total amount of solid matter in sewage 
taken from various main sewers comes to 94 grains per gallon 
during the day-time, and 79 grains during the night; giving an 
average for the whole day and night of 86 gi'ains. But on 
putting together 24 of the analj-ses — 25 Avere made altogether, 
but I reject one, because it contained an enormously large quan- 
tity of solid matter — taking 24 normal analyses of Dr. Letheby, 
and grouping them into two classes, the one showing less and the 
other more than 86 grains, I find in the former class 15 analyses 
furnishing on an average only CG grains of solid matter in the 
imperial gallon, and in the other nine samples yielding on an 
average 123 grains. Kow, considering that this occasional excess 
of solid matter takes jdace especially on rainy days, and is due 
mainly to the wasliings of the streets, and therefore principally 
