Fhosphntic Materials medfor Agricultural Purposes. 357 
and Is used in Germany for the making? of superphosphate, but 
as yet it has not found its way into England. 
Another species of phosphorite, distinguished by the name of 
osteoUth, was discovered some years ago near Hanau, in 
Crcrmany. It occurs in thin seams in a volcanic rock, is soft 
and almost white, and very rich in phosphate of lime. Unfor- 
tunately the seams of this osteolith are not of sufficient thickness 
to repay the cost of excavation, consequently no practical appli- 
cation has been made of it as yet. 
3. Cambridgeshire Coprolites. 
The phosphatic nodules of the lower chalk are known in 
commerce under the name of Cambridgeshire coprolites. Their 
physical character and the localities where they are found are so 
well known that 1 need not dwell on these points. 
The composition of different average samples, obtained by 
reducing to powder several tons, varies to some extent. In some 
more carbonate of lime and insoluble siliceous matter occur 
than in others, and consequently the amount of phosphate of lime 
in different samples fluctuates to a certain degree. 
In commercial analyses it is usual to deteimine the amount of 
phosphate of lime or bone-earth by digesting the finely-powdered 
coprolites in hydrochloric acid, filtering off the solution from the 
insoluble siliceous matter, and precipitating the phosphates with 
amm(mia. However careful the analyst may be to employ 
ammonia perfectly free from carbonic acid, and to avoid contact 
with the air, some carbonate of lime invariably falls down with 
the precipitated phosphates. It is necessary, therefore, to redis- 
solve the latter in hydrochloric acid, and to throw them down a 
second time with ammonia. If this be neglected, the amount of 
phosphates in coprolites, and in all other phosphatic substances 
containing carbonate of lime, is determined too high. 
By way of example, the following commercial analyses of 
powdered Cambridgeshire coprolites are given : — 
General Composition of Cambridgeshire Coprolites. 
Xo. 
1. 
Xo. 
2. 
Xo. 
3. 
Xo. 4, 
Xo. 
5. 
No. 
6. 
Moisture and a little 1 
02 
49 
44 
organic matter . . J 
.3 
11 
4 
3 
4-45 
4 
01 
3 
62 
32 
61 
04 
59 
67 
61-06 
61 
40 
61 
90 
Carbonate of lime, "j 
magnesia, alkalies, i 
and fluorine (deter- 1 
28 
67 
42 
27 
30 
65 
28-37 
28 
37 
29 
36 
mined by difierence)] 
Insoluble siliceous mat-1 
15 
19 
0-12 
6 
7 
27 
6 
6 
22 
5 
24 
100 
00 
100 
00 
100 
00 
100-00 
100 
00 
100 
00 
