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IV. On the Existence of Phosphoric Acid in Rocks of Igneous Origin. By George 
Fownes, Ph. D., Chemical Lecturer in the Middlesex Hospital Medical School. 
Communicated hy Thomas Graham, Esq., F.R.S., 8$c. 8$c. 
Received April 17, — Read April 25, 1844. 
The important although obscure functions attributed to the elementary body 
phosphorus, both in the vegetable and in the animal kingdoms, and the well-known 
fact that rocks of nearly every description afford on disintegration soils more or less 
capable of supporting the life of plants, and from which consequently phosphoric acid 
cannot possibly be absent, seemed to render a search for that substance in rocks of 
igneous origin generally very desirable, because if there found, an easy and satisfactory 
explanation of the origin and first source of the element in question would be given. 
As I am not aware that any direct researches on this subject have yet been made, 
or at least placed on record, I venture to submit to the notice of the Royal Society 
the results of a few experiments made by myself, which, so far as they go, resolve the 
question in the affirmative. 
The first substance tried was the fine white porcelain-clay of Dartmoor, Devon, 
the result of the disintegration of the felspar of the granite of that district. This is 
one of the chief components of porcelain and of the finer kinds of English earthen- 
ware, and was found on analysis to correspond very closely in composition with that 
of the material employed in the manufacture of the Sevres porcelain. It was thought 
that phosphoric acid, if present, would be in combination with a portion of the 
alumina ; and as the phosphate of that earth is readily soluble in dilute mineral acids, 
while the silicate offers great resistance to these agents, mere digestion with acid 
would suffice to extract the whole, or the greater part of the phosphate, which could 
be afterwards precipitated by an alkali, and examined. 
With this view, 1000 grains of the clay were boiled during several hours in a flask 
with a quantity of pure dilute hydrochloric acid ; a large bulk of distilled water was 
then added, and the whole allowed to rest until perfectly clear. The acid liquid was 
then carefully decanted from the undissolved clay, evaporated in a porcelain basin to 
a small bulk, and precipitated by a slight excess of pure ammonia. The scanty, 
reddish precipitate obtained, which consisted chiefly of alumina and oxide of iron, 
was collected upon a little filter, thoroughly washed with distilled water, dried, and 
ignited. It was next reduced to fine powder, and mixed with an equal weight of pure 
silica in a finely-divided state, and six times as much anhydrous carbonate of soda. 
This mixture was heated to fusion in a platinum crucible. When cold, the melted 
