358 Chemical Composition and Commercial Value of 
" As both chalk-copiolitcs and Suffolk-coprolites contain much 
fluoride of calcium, by determining the amount of phosphates 
in the usual way by precipitation, fluoride of calcium is thrown 
down with the precipitate, in consequence of which the amount 
of ])hosphate of lime (bone-earth) is stated three to four per cent, 
higher than it is in reality. The true amount can only be 
correctly estimated by determining the percentage of phosphoric 
acid which they contain, and calculating from this acid the 
amount of bone-earth. In order to ascertain the true proportion 
of ])one-earth in coprolites, and at the same time the exact 
quantity of other constituents which take up the sulphuric acid 
with which coprolite powder is mixed in the manufacture of 
superphosphate, I have made several detailed analyses of average 
samples of Cambridgeshire coprolites, and obtained the following 
results : — 
Detailed Composition of Average Samples of Camhridgeshire Coprolites, 
No. 1. No. 2. '^0.3. 
Moisture and organic matter . . . . 4-63 4"01 3"52 
Lime 43-21 45-39 46-60 
Magnesia 1-12 -48 1-06 
Oxide of iron 2-46 1-87 2-08 
Alumina 1-36 2-57 1-41 
♦Phosphoric acid 25-29 26-75 27-01 
tCarbonic acid 6-66 5'13 5-49 
Sulphuric acid -76 1-06 {^,^^^5^,,^ 
Chloride of sodium -09 traces traces 
Potash -32 -84 ( not 
Soda -50 '73 t determined 
Insoluble siliceous matter 8-64 6*22 6-04 
Fluorine and loss 4-96 4-95 6-79 
100-00 100-00 100-00 
* Equal to tribasic phosphate of lime"* 54.89 ST-f 58-52 
(boue-earth) J ' o - 
t Equal to carbonate of lime .. .. 15-13 11-66 12-47 
Amount of phosphates, determined! 01-40 60-81 
in the usual way by precipitation ) ' ' ' 
It will be seen that in the second sample the amount of phos- 
phates obtained by precipitation is, in round numbers, four per 
cent, higher, and in the third sample two per cent, higher, than 
that resulting from the more accurate method of determining the 
percentage of phosphoric acid, and calculating from it the 
amount of bone-earth. 
Powerful machinery is recjuired for reducing coprolites to a 
fine powder. Coarse coprolite powder is not easily acted upon 
by acid, and has little or no effect upon vegetation. It is there- 
fore advisable to reduce coprolites to a minute state of sub- 
division, and to digest them afterwards with a quantity of acid 
sufficient to saturate all the carlwnate of lime and other con- 
