116 HOW CROPS FEED. 
is of almost universal occurrence in small quantities. Some 
forms of it easily oxidize when exposed to air, and furnish 
the green-vitriol (sulphate of protoxide of iron) of com- 
merce. 
Apatite and Phosphorite.—These names are applied to 
the native phosphate of lime, which is usually combined 
with some chlorine and fluorine, and may besides contain 
other ingredients. Apatite exists in considerable quantity 
at Hammond and Gouverneur, in St. Lawrence Co., N: 
Y., in beautiful, transparent, green crystals; at South 
Burgess, Canada, in green crystals and crystalline masses ; 
at Hurdstown, N. J., in yellow crystalline masses; at 
Kragerée, Norway, in opaque flesh-colored crystals. In 
minute quantity apatite is of nearly universal distribution. 
The following analyses exhibit the composition of the 
principal varieties. 
Kragerée, Hurdstown, 
Norway. New Jersey. 
Voelcker. J. D. Whitney. 
Lime, 53.84 53.37 
Phosphoric acid, 41.25 42.23 
Chlorine, 4.10 1.02 
Fluorine,* 1.23? ? 
Oxide of iron, 0.29 trace 
Alumina, 0.38 
Potash and soda, 0.17 
Water, 0.42 
Phosphorite is the usual designation of the non-crystal- 
line varieties. 
Apatite may be regarded as a mixture in indefinite 
proportions of two isomorphous compounds, chlorapatite 
and fluorapatite, neither of which has yet been found pure 
in nature, though they have been produced artificially. 
* Fluorine was not determined in these analyses. The figures given for this 
element are calculated (by Rammelsberg), and are probably not far from the truth, 
