245 
temperature, and the carbonate of soda added as long as effer- 
vescence continues; filtering to separate phosphate of lime 
and magnesia, boiling the liquid down, and leaving it to crys- 
tallize.’ 
‘¢T will not occupy the time of the Academy by proving 
that the assertion, that this precipitate is carbonate of lime is 
utterly erroneous; the most trifling examination shows that 
it is a phosphate of lime of some kind. Berzelius and Gmelin 
thought, as is evident from the extracts quoted, that it was 
identical with bone earth, for they never apply the simple name 
of ‘ phosphate of lime’ to any other compound ; and they were 
probably led to this opinion by the knowledge of the fact, that 
when bone earth is dissolved by nitric, hydrochloric, or acetic 
acids, it is precipitated by an alkali unchanged. ‘This is easily 
intelligible by an equation : 
PO; 3CaO+2ChH=PO; CaO 2HO+2CaCh. 
It will be here seen, that a mono-phosphate of lime and chlo- 
ride of calcium are formed (supposing hydrochloric to be the 
acid employed), and both these dissolve. Let an alkali (am- 
monia) be now added, and the following will take place: 
PO; CaO 2HO+2CaCh+2NH;=PO, 3 CaO 
+ 2NH, Ch. 
The two equivalents of lime which had been abstracted and 
decomposed by the hydrochloric acid are re-formed, and, going 
back to the mono-phosphate, regenerate bone earth. 
«¢ But it will be seen that this reproduction of the bone- 
earth is due to the whole of the lime being retained in the so- 
lution; the case is different when sulphuric acid acts upon 
bone ashes. Dobereiner and Berzelius have shown that the 
action of sulphuric acid on bone earth varies according to the 
quantity of acid employed ; but in any case the lime subtracted 
by the acid is rendered insoluble, and thus removed from the 
liquid. A possible decomposition is the following : 
