value in kelp, the form in which it
can be most cheaply purchased.

_Nitrate of Soda_ is usually sold at from L15 to L15: 10s. per ton, and,
making allowance for impurities, L16 may be taken as the value of the
pure salt.

_Biphosphate of Lime, Soluble Phosphates._--Considerable difficulty is
experienced in estimating the value of these substances, because they
are not met with in commerce alone, or in any form except that of
superphosphate, and the prices at which they are sold in different
samples of that manure differ excessively. The only course by which any
result can be obtained, is to determine the average price of a good
superphosphate, and putting the values already ascertained on all the
other constituents to reckon the difference between that sum and the
market price as the value of soluble phosphates. Throwing out, as
inferior, all samples containing less than 10 per cent of soluble
phosphates, and taking the good only, I find that the average
composition of the phosphates in the market during the present year has
been--

Water 10.71
Organic matter 9.33
Biphosphate of lime equivalent to 19.43
"soluble phosphates" 12.45
Insoluble phosphates 14.78
Sulphate of lime 45.24
Alkaline salts 2.11
Sand 5.38
------
100.00
Ammonia 1.71

It is more difficult to fix the average price of superphosphate, as in
many cases no information could be obtained on this point; but among
those analyzed were samples at all prices, from L7 up to L10: 10s. per
ton, so that on the whole, L8 may be assumed as an average, and in that
case soluble phosphates are worth L27: 19s. per ton. Had the inferior
samples been included, the price would have been higher, and in fact the
rate at which soluble phosphates have been commonly estimated is L30 per
ton, or L46: 16s. for biphosphate of lime, although sometimes the former
have been reckoned as low as L25, with a corresponding rate for the
latter. It is important that biphosphate of lime and soluble phosphates
should not be confounded with one another in valuing a manure, the
latter having one and a half times the value of the former.

As manures are liable to considerable fluctuations i