178 ARTIFICIAL MAN URES. 
insoluble phosphates. Scientific opinion on this point 
is, at present, in a state of transition, as there is no 
doubt this rule bears too hardly upon the manufac- 
turer. Provided the insoluble phosphate is in a fine 
state of division, a value should be allowed to it for 
two reasons. First, it may consist of phosphate that 
has not been dissolved, in which case its value, pro- 
vided of course it be phosphate of lime not phosphate 
of alumina, should be considered equal to phosphate 
in ground coprolite. However, as undissolved mineral 
phosphate is almost universally considered greatly in- 
ferior to undissolved bone phosphate, the rule would 
have a decidedly salutary effect in causing manufacturers 
to turn all the phosphate into the soluble form ; but 
it happens that what is condemned as insoluble mi- 
neral phosphate commonly contains a proportion of 
dissolved phosphate that has reverted to an insolu- 
ble form which is little inferior and probably in the 
potent climate of Ceylon is quite equal to the soluble 
phosphate, so that it is a manifest injustice to the 
manufacturer not to allow anything for it because it 
is practically insoluble in water. Some eminent che- 
mists hold that all the soluble phosphate reverts to 
the form insoluble in water in the soil before it is 
taken up by the plant and that the only advantage 
which the initial solubility gives it, is a greater 
diffusive power before it reverts. When alkaline sub- 
stances such as ashes are mixed with soluble phos- 
phates much of the latter reverts. 
In Belgium, agricultural chemists are decidedly ahead 
of us in their mode of valuing phosphates. Mr. K. 
Walter, Chemical Engineer, Aurelais, Belgium, informs 
us in the Chemical News, ‘‘that it was announced that 
from the Ist January 1878 in all phosphates coming 
under the control of the Belgian agricultural stations, 
all phosphoric acid soluble in citrate of ammonia must 
be counted assimilable and of the same value as 
soluble in water.” The same authority informs us, 
‘‘‘there are soils in which a given weight of a 
natural phosphate of say 20 per cent of phosphoric 
acid has the same effect as the same weight of 
superphosphate of 12 to 14 per cent. of phosphoric 
acid; but the price of the first would be £1 15s or less, 
while the price of the latter is at least £4 per ton.” 
And again, ‘‘ Some of the French mineral phosphates 
when finely ground are excellent manure. For fresh 
broken woodland, turfy ground and soils rich in humic 
acids they are superior to superphosphates. ” 
The careful experiments of Mr. Thomas Jamieson, 
F.C. S., chemist to the Aberdeenshire Agricultural 
Association, led him to the conclusion ‘‘that for the 
