370 Chemical Composition and Commercial Value of 
tlie phosphoric acid as tribasic phosphate of lime, the ammonia 
precipitate, which is still erroneously assumed by many to be 
8 C O 4- 3 P Oj, is recalculated as tribasic phosphate of lime. 
This practice deserves to be strongly condemned, lor it leads to 
wrong results, giving invariably the amount of tribasic phosphate 
much higher than it is in reality. Great discrepancies in the 
determinations of phosphate of lime in bone-ash, tScc, by different 
analysts, are a source of constant annoyance and frequent disputes 
between seller and buyer. As long as the practice prevails of 
ascertaining the phosphates simply by precipitation, such dis- 
crepancies must remain matters of almost daily occurrence. 
It is, of course, a much more expeditious plan to determine 
the phosphates by precipitation than to ascertain correctly the 
amount of phosphoric acid ; but if we consider the difference 
that an error of 3 or 4 per cent, of phosphate of lime will make in 
the value of a ship's cargo, we shall admit that accuracy ought not 
to be sacrificed to expedition. There is, indeed, ground to fear 
that analyses are carried out in a too commercial — nay, often a too 
interested — spirit, such as is calculated to bring analytical che- 
mistry into disrepute. It is therefore the duty of all desirous of 
carrying out analytical investigations in a manner consistent 
with truth to raise a strong opposition against the mode in which 
more especially commercial analyses of bone-ash and animal 
charcoal are frequently executed at present. 
I have myself repeatedly analysed the ammonia precipitate 
from bone-ash, and arrived at the conclusion that, imder 
the most favourable circumstances, it never contains less than 
3 equivalents of lime for 1 equivalent of phosphoric acid. 
Generally, however, it contains an additional quantity of lime, 
or, more correctly speaking, carbonate of lime, — for I find it 
extremely difficult to prevent more or less carbonate of lime 
from falling down with the phosphates when precipitating the 
latter with ammonia. This is especially the case when the pre- 
cipitation is effected in a hot solution. Notwithstanding the 
entire absence of carbonic acid in the ammonia used for preci- 
pitation, and the observance of every precaution to exclude the 
air from the precipitated phosphates, some additional lime beyond 
the proportion required to combine with phosphoric acid to form 
tribasic phosphates is invariably found in the precipitate obtained 
from a boiling-hot solution, even after the precipitate has been 
re-dissolved and thrown down again a second or third time. If, on 
the contrary, the precipitation is effected in the cold, and the phos- 
phates are re-dissolved in acid after washing with ammonia- 
water, and thrown down again a second time with pure ammonia 
from a dilute cold solution, I find their composition agrees closely 
with tribasic ])hosphate of lime. Thus from a sample of bone- 
