fully equal to the figures given by Lawes
and Gilbert. If we call the nitrogen worth 20 cents a lb., and the
phosphoric acid (soluble) worth 12-1/2 cents, a ton of such urine would
be worth, _on the land_, $1.06.

"A ton of the fresh faeces," said the Deacon, "at the same estimate,
would be worth (20 lbs. nitrogen, at 20 cents, $4; 21-3/4 lbs.
phosphoric acid, at 12-1/2 cents, $2.70), $6.70."

"Not by a good deal," said the Doctor. "The nitrogen and phosphoric acid
in the urine are both soluble, and would be immediately available. But
the nitrogen and phosphoric acid in the faeces would be mostly
insoluble. We cannot estimate the nitrogen in the faeces at over 15
cents a lb., and the phosphoric acid at 5 cents. This would make the
value of a ton of fresh faeces, _on the land_, $4.09."

"This makes the ton of faeces worth about the same as a ton of urine.
But I would like to know," said the Deacon, "if you really believe we
could afford to pay $4 per ton for the stuff delivered on the farm?"

"If we could get the genuine article," said the Doctor, "it would be
worth $4 a ton. But, as a rule, it is mixed with water, and dirt,
and stones, and bricks, and rubbish of all kinds. Still, it is
unquestionably a valuable fertilizer."

"In the dry-earth closets," said I, "such a large quantity of earth has
to be used to absorb the liquid, that the material, even if used several
times, is not worth carting any considerable distance. Dr. Gilbert found
that 5 tons of absolutely dry earth, before using, contained 16.7 lbs.
of nitrogen.

After being used _once_, 5 tons of the dry earth contained 24.0 lbs.
" " " twice, " " " " " 36.3 "
" " " three times, " " " " " 44.6 "
" " " four times, " " " " " 54.0 "
" " " five times, " " " " " 61.4 "
" " " six times, " " " " " 71.6 "

Dr. Voelcker found that five tons of dry earth gained about 7 lbs. of
nitrogen, and 11 lbs. of phosphoric acid, each time it was used in the
closets. If we consider each lb. of nitrogen with the phosphoric acid
worth 20 cents a lb., 5 tons of the dry earth, after being used once,
would be worth $1.46, or less than 30 cents a ton, and after it had been
used six times, five tons of the material would be worth $11.98, or
about $2.40 per ton.

In this calculation I have not reckone