148 
Superphosphate of Lime. 
acid only be employed, the mixture is white, from the carbonate 
of lime which then predominates. From an average taken from 
several analyses of bones of man and various animals, the fol- 
lowing appears to be tolerably near the mean : — 
Organic matter, consisting of gelatine, cartilage, and fat 34 
Phosphates of lime and magnesia . . . .59 
Carbonate of lime ...... 7 
100 
Or, in rough numbers, the organic matter may bis regarded as 
forming one-third, and the earthy portions two-thirds. Of course 
if the bones are very fresh the former will be in larger proportion 
than one-third ; thus Mr. Hannam gives it as 45 per cent. The 
above, however, may be considered as a fair average in the state 
usually employed by farmers. 
Four bushels of bones, which may be considered to be a fair 
allowance for an acre, will weigh in a fine state of bone-dust 
about 180 lbs * This quantity contains 12^ lbs. of carbonate 
of lime, consisting of carbonic acid 5^ parts, and lime 7 parts, 
which will require 10 lbs. of sulphuric acid to convert it into 
sulphate of lime or gypsum. This is the first result of the mix- 
ture, and is the cause of the very unpleasant fumes which are 
given off, and which consist in fact principally of carbonic acid 
disengaged from the carbonate of lime in consequence of the 
superior affinity which lime has for sulphuric acid. This result 
takes place before the acid acts on the phosphates of the bones, 
and thus it is that when a small quantity of acid has been sprinkled 
over bone-dust the good effect has been but moderate, the car- 
bonate of lime alone has been acted on, and the phosphate of 
lime has remained undecomposed. 
The quantity of phosphate of lime existing in the 4 bushels 
of bones is about 106 lbs., containing 47 lbs. of lime and 59 lbs. 
of phosphoric acid. If we consider superphosphate of lime to 
contain a double portion of acid — a fact, however, not quite de- 
cided, then 33 lbs. of sulphuric acid will be required, which by 
uniting with half the lime, or 23<^ lbs., forms gypsum, and leaves 
the other moietv of lime united with a double portion of phos- 
phoric acid in the state of a superphosphate. Thus 43 lbs. of 
acid will be required to effect these changes, leaving any addi- 
tional quantity for other purposes, j 
* I find that the average weight of bone-dust, as it comes from the mill, 
is IGSlbs. j)er 4 bushels, although I have found it reach the weight stated 
in the text. — Aut. 
t I do not mean to say that these are the precise changes which 
take place, but only an approximation to them. Probably some portion 
of phosphoric acid may be left in a free state in the prepared mixture. 
