PImpliniic Materials used for Afjricultimil Purposes. 
most other varieties of apatite. Tlie amount of chloride of 
calcium, I find, varies from 2*16 to 6"41 per cent, in pieces 
chipped off the same block, showing that large blocks are not 
always uniform in their composition. 
The preceding analyses were made some years ago. Quite 
recently I analysed a sample of ground Norwegian apatite, which 
yielded the following results : — 
Moisture (driven oft' at 212° F.) -24 
Water of combination "66 
Lime 45-12 
'Chloride of calcium 2*53 
Magnesia '74 
Oxide of iron 1-29 
Alumina 1'53 
Potasli "36 
Sulphuric acid "29 
t Phosphoric acid 35'69 
Insoluble siliceous matter 11'62 
100-07 
* Containing chlorine 1'62 
t Equal to tribasic phosphate of lime (3 Ca 0,"l — .„„ 
P O, = bone-earth) / " 
This sample, like all those from Krageroe in Norway which 
I have hitherto examined, does not contain a trace of fluorine. 
It is likewise free from carbonate of lime, but contains more 
siliceous matter, and also more oxide of iron and alumina than 
the cargoes imported from the same locality in former years. 
These impurities necessarily reduce the percentage of phosphate 
of lime, which, however, is still very considerable in the last- 
mentioned sample. 
I have already noticed that the composition of the uhground 
mineral is not quite uniform. In some pieces fragments of 
quartz, hornblende, and other foreign minerals, can be seen with 
the naked eye. In order, therefore, not to be misled by the 
analyses of picked specimens, it is necessary to reduce to a fine 
powder a considerable quantity of the mineral, say five or ten 
cwts., and to have an analysis made of such a mixed average 
sample. 
2. Spanish Phosphorite (Estkamadura Phosphate). 
This mineral occurs in immense quantities at Lagrosa, near 
Tuxillo, in Estramadura. It is here associated with foliated 
apatite and quartz, and forms solid beds that alternate with 
limestone and quartz. This Spanish phosphorite has a fibrous 
structure, a light yellow colour, and a considerable degree of 
hardness. Reduced to powder, and placed upon a heated piece 
