Soluble and Insoluble Phosphates. 
153 
that the manufacture of superphosphate, in which millions of 
pounds sterling are embarked, has been established on unsound 
princij)les, and carried on for more than twentj-five years to the 
disadvantage of the farmer. 
It is not my intention to make any critical remarks on 
Mr. Jamieson's field-experiments, nor to controvert his bold 
assertion that the results of the Aberdeenshire field-experiments 
will cause a complete revolution in the manufacture of artificial 
manures ; but I propose simply to direct attention to a few pub- 
lished experiments which are diametrically opposed in their 
results to those which Mr. Jamieson has obtained, and which 
conclusively prove the economy and beneficial effects of dissolved 
phosphatic manures in comparison with the raw materials from 
which they are manufactured. It will be admitted by all persons 
that, in order to be food for plants, phosphate of lime, like 
other constituents of plant-food, must be soluble to some extent 
in water, or in the liquid which passes through the medium 
of the root into the plant. Although we are in the habit of 
speaking of insoluble phosphate of lime, no phosphate of lime, 
not even the hardest and most crystalline variety, is absolutely 
insoluble in water, especially when the water is charged with 
more or less carbonic acid. Some of the beds of the Lower 
Chalk formation, and certain marls in the Greensand for- 
mation, it is well known, are more efficacious fertilisers than 
the chalk and marls in the Upper Chalk formation, mainly 
because they contain more or less considerable proportions of 
phosphate of lime, of which no appreciable quantities occur in 
the latter formation. There cannot be any question about the 
fact that, in the shape of marl or chalk, mineral phosphate of 
lime is soluble in water charged with carbonic acid, and that 
phosphatic marls and chalk are better fertilisers than marls or 
chalk in which phosphate of lime is absent, or present only in 
minute proportions. I do not therefore deny for a moment that 
insoluble mineral phosphate of lime has fertilising properties. 
It will also be admitted that the more finely the phosphate of 
lime is divided, the more easily it will be acted upon by water ; 
or, in other words, that in a finely divided state phosphate of 
lime is soluble to a greater extent in water, and is more effi- 
cacious as a manuring agent than in a coarser state of division. 
In a paper published by me in 1868, in the ' Journal of the 
Royal Agricultural Society,' on the "Solubility of Phosphatic 
Materials," I gave experimental evidence of the varying degree 
of solubility of various forms in which phosphate of lime occurs 
in coarse and fine bone-dust ; in Peruvian and phosphatic guanos ; 
in bone-ash and porous mineral-pliosphates ; in coprolites ; in 
different kinds of hard and crystalline phosphatic minerals, 
