PURE PHOSPHORIC ACID FROM BONES. 49 
As this salt was evidently formed at a certain temperature, I could see no 
reason why the whole of the magnesia might not be converted into that insoluble 
form, although, in this first experiment, the filtered liquid was found to contain 
much magnesia. I therefore again evaporated the filtered solution; and, at the 
same temperature as before, it again became turbid. I kept up the same heat 
for fifteen minutes; and when the mass, after cooling, was acted on by water, a 
large quantity of the insoluble phosphate separated, and the filtered liquid was 
now found absolutely free from the smallest trace of magnesia. It now clearly 
appeared that the first heating had been too short, and that it was only necessary 
to heat long enough to bring every part of the mass to the same temperature. 
The process which I recommend, therefore, is as follows:—The glass re- 
maining, after heating to redness in a covered platinum crucible to expel sulphuric 
acid (after the separation by that acid of all the lime), is to be boiled in water, 
and the solution evaporated, and, finally, exposed in a platinum capsule for a quar- 
ter of an hour, to a heat of from 595° to 600°, or to that temperature at which 
the acid begins to volatilize with the water. ‘Tt must not be heated more strongly, 
lest the glass should be reproduced. When cold, the mass is to be softened with 
water, and the solution of pure phosphoric acid filtered from the insoluble phos- 
phate of magnesia. The acid is pure from magnesia, if, when diluted and super- 
saturated with ammonia, it forms no deposit, especially after standing for one 
or more days. I have repeated the process six or seven different times, and on 
no one occasion did the filtered acid contain magnesia, except when I had pur- 
posely heated too strongly. This proves that the degree of heat is not difficult 
to manage. Indeed, after the first experiment I found it unnecessary to use 
the thermometer, the appearance of the mass furnishing a sufficient guide. It is 
evident that the above process has the twofold advantage of simplicity and 
economy. 
The quantity of magnesia which separates in the form of the insoluble phos- 
phate is very considerable. It will be very easy to determine exactly the amount 
of magnesia in bone-earth, by converting it into this salt. 
II. On a new and anomalous Phosphate of Magnesia. 
This is the salt so often mentioned above, as being separated by a heat of 
600° from its solution in phosphoric acid. As the salt is perfectly anhydrous, it 
is obvious that its formation is owing to the separation of water at that high tem- 
perature. The analysis of the salt was made by fusing with carbonate of soda, 
dissolving in diluted hydrochloric acid, adding, for precaution’s sake, a little phos- 
phate of soda, and then precipitating by ammonia, collecting the ammoniaco- 
magnesian phosphate on a filter, washing moderately with cold water, drying 
and igniting. The residue, pyrohposphate of magnesia, was reckoned to contain 
VOL. XVI. PART I. N 
