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6 Experiments and Observations 
phate of lime. The bones I used were those 
of graminivorous animals indiscriminately. 
The nature of the earth of bones being 
thus known, it is pretty easy to see what 
must take place when sulphuric acid is added 
to them. The acid first expels the carbonic 
acid and seizes that part of the lime which 
may be considered as free. It then attacks 
the phosphate of lime, part of which it de- 
composes, takes the lime, and sets the phos- 
phoric acid at liberty; but this last immedi- 
ately joins the remaining phosphate of hme 
and constitutes a superphosphate; at length 
this superphosphate of lime gets so surround- 
ed with phosphoric acid that the sulphuric is 
unable to make any further change or decom- 
position. Then, as the sulphate of lime is 
nearly insoluble and consequently precipitates, 
there remains in the liquid the soluble super- 
phosphate of lime, sulphuric acid (if it have 
been used in excess), and a minute portion of 
sulphate of lime. This last may be got out 
by evaporating the liquor to dryness and then 
dissolving again in a minimum of water; the 
excess of sulphuric acid may be taken out by 
adding barytic water or carbonate of bary- 
tes as long as any precipitate appears; and 
then the superphosphate of lime remains alone 
in solution. 
