54 
DR. FOWNES ON THE EXISTENCE OF PHOSPHORIC ACID 
mass was acted upon by boiling water, and the soluble and highly alkaline portion 
separated by a filter from the insoluble silicate of alumina. The solution was mixed 
with excess of nitric acid, evaporated to dryness, water added, and the product 
filtered. The liquid thus obtained was divided into two portions ; one of these was 
carefully neutralized bv a little ammonia, and mixed with a few drops of solution of 
nitrate of silver ; a distinct yellow precipitate appeared, which was freely soluble in 
dilute nitric and in acetic acids. The second portion was mixed with excess of am- 
monia and some hydrochlorate of ammonia, and a few drops of solution of sulphate 
of magnesia added. After a short interval, a crystalline, granular, white precipitate, 
the ammonio-magnesian phosphate, made its appearance, which increased in quantity 
bv agitation. 
This experiment, which demonstrates the presence of a small quantity of phos- 
phoric acid in the clay, in a most • unequivocal manner, was several times repeated 
with a like result. The purity of the acids, carbonate of soda, and other materials 
employed, were rigorously tested, and filtration through paper of the original acid 
liquid purposely avoided, lest a trace of earthy phosphate should have been dissolved 
from the paper. 
The porcelain-clay is extracted from the disintegrated granite by mere washing 
with water, and subsidence, and the water of the district in which it is found is, in 
all probability, exceedingly pure. It was thought worth while, however, to examine 
in the same manner the decomposed rock which had not been subjected to any arti- 
ficial treatment, and a specimen taken by myself from the quarry was chosen for the 
purpose. The result showed the presence of phosphoric acid as in the clay, and 
apparently to about the same extent, allowance being made for the quartz-grains, 
mica, &c. 
In the examination of unaltered felspar, I failed, unfortunately, in getting a con- 
clusive result. The mineral, although reduced to very fine powder by trituration in 
a mortar of Swedish porphyry, was found to be so hard and dense as to resist com- 
pletely the action of the acid at a boiling temperature. An insignificant quantity 
of oxide of iron was dissolved out, in which no phosphoric acid could be detected. 
200 grains of the powdered felspar were then fused with a large excess of carbonate 
of soda; the mass was treated with water, filtered, the solution supersaturated with 
nitric acid, and evaporated to dryness: water was poured upon the residue, and the 
whole placed upon a filter. The solution was then examined, as before, for phosphoric 
acid, but with an indistinct and doubtful result. Too small a quantity of the felspar 
had been used, and the mass of nitrate of soda present interfered too seriously with 
the action of the tests to render their evidence of any value. A far better mode of 
investigation would be, to act upon the powdered mineral with hydrofluoric acid, in 
the manner recommended by some analysts in the examination of natural silicates 
containing an alkali ; not being, however, in possession of the necessary platinum ves- 
sels, I was obliged to abandon the attempt. 
