8 Chemical Composition and Commercial Value of 



most other varieties of apatite. The 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 : 



4 Moisture (driven off at 212 F.) -24 



Water of combination '66 



Lime 45-12 



*Chloride of calcium 2'53 



Magnesia '74 



Oxide of iron 1*29 



Alumina T53 



Potash -36 



Sulphuric acid *29 



t Phosphoric acid 35'69 



Insoluble siliceous matter 11*62 



100-07 



* Containing chlorine T62 



t Equal to tribasic phosphate of lime (3 Ca Q,\ 

 P 5 = bone-earth) / ' 7 ' 3< 



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 unground 

 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 (ESTRAMADURA 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 



