ssary, and none is used. The
water in the guano and in the acid is sufficient to furnish the two
atoms of water for the phosphate, and the two atoms for the sulphate of
lime."

"Such is undoubtedly the case," said I, "and when large quantities of
superphosphate are made, and the mixing is done by machinery, it is not
necessary to use water. The advantage of using water is in the greater
ease of mixing."

"Bone-dust," said the Doctor, "contains about 6 per cent of water, and
the sulphuric acid (sp.g. 1.7) contains about one-third its weight of
water. So that, if you take 620 lbs. of bone-dust, and mix with it 240
lbs. of common sulphuric acid, you have in the mixture 117 lbs. of
water, which is 45 lbs. more than is needed to furnish the water of
combination."

"The superphosphate produced from 620 lbs. of bones, therefore,"
continued the Doctor, "would contain:

Phosphoric acid} {142 lbs.
Lime } acid phosphate { 56 "
Water } { 36 "

Sulphuric acid } {160 lbs.
Lime } sulphate of lime {112 "
Water } { 36 "

Organic matter, ash, etc., of the bones [A] 335 "
--------
Total _dry_ superphosphate 877 "
Moisture, or loss 45 "
--------
Total mixture 922 lbs.

[A] Containing nitrogen, 23-1/2 lbs.

"There is a small quantity of carbonate of lime in the bones," said I,
"which would take up a little of the acid, and you will have a
remarkably good article if you calculate that the 620 lbs. of bone-dust
furnish you half a ton (1,000 lbs.) of superphosphate. It will be a
better article than it is practically possible to make."

"Assuming that it made half a ton," said the Doctor, "it would contain
14-1/4 per cent of soluble phosphoric acid, and 2-1/3 per cent of
nitrogen."

"With nitrogen at 20 cents per lb., and soluble phosphoric acid at
12-1/2 c. per lb., this half ton of superphosphate, made from 620 lbs.
of good bone-dust, would be worth $22.50, or $45 per ton."

"Or, to look at it in another light," continued the Doctor, "a ton of
bone-dust, made into such a superphosphate as we are talking about,
would be worth $72.58."

"How much," asked the Deacon, "would a t