?)72 Cliemiral Compo.tif ion tind Commercial Value of 
nsa'^os less abrupt, phosphoric acid, equal to say 74 or to 76 per 
cent, of tribasic phosphate of lime, as the case may be. If this 
sugsi'estion were generally adopted, all squabbles respecting the 
composition of bone-earth would be set aside. By stating the 
amount of phosphoric acid which was actually found in the 
analysis, and the corresponding percentage of tribasic phosphate 
of lime, it would be seen at once that a reliable method, and not 
the uncertain process of precipitation, had been employed by the 
analyst. 
The con'ect determination of phosphoric acid is attended with 
a good deal of trouble, and necessitates much care and experience 
on the part of the operator. 
The method of analysing bone-ash which I have adopted in 
my laboratory yields most satisfactory results ; and, as it may be 
useful to others, I will give a brief outline of it. 
Moisture and organic matter are determined as usual. About 
twenty grains of finely-powdered bone-ash are carefully dissolved 
in hydrochloric, or better in nitric, acid ; the solution is evaporated 
to dryness in a waterbath. By this means any pyrophosphate 
which may be present in the bone-ash is converted into the 
ordinary phosphate, and the soluble silica which always occurs 
in commercial bone-ash is rendered insoluble. The dry residue 
is taken up in the smallest possible quantity of nitric acid, and 
the sand filtered off ; the solution passing through the filter is 
heated to the boiling-point, and precipitated with an excess of 
oxalate of potash or ammonia. The oxalate of lime held in 
solution by the liberated oxalic acid is thrown down with the 
first precipitate of oxalate of lime by neutralising the liquid with 
caustic potash or soda, by adding afterwards an excess of oxalate 
of potash or soda, and l)oiling. The oxalate of lime is removed 
])y filtration, and the filtrate and washings evaporated to a small 
])ulk, and finally the phosphoric acid precipitated with ammo- 
niacal sulphate of magnesia. To prevent any oxide of iron or 
alumina, which occasionally are present in commercial bone-ash, 
from falling down with the phosphate of magnesia, it is desirable 
to add a little tartaric acid to the liquid before precipitating the 
phosphoric acid. 
The precipitated phosphate of magnesia has to be set aside 
for at least twelve hours before it may be safely collected on a 
filter. As an excess of oxalate of potash has to be used for the 
determination of lime, and an excess of ammoniacal sulphate of 
magnesia for the determination of the phosphoric acid, oxalate 
of magnesia is formed, Avhich, after standing for a time, 
separates and falls down with the phosphate of magnesia, unless 
a very large amount of ammoniacal salts is present. I find, 
indeed, that the phosphate of magnesia obtained in this kind of 
