CHAPTER XII.
MINERAL PHOSPHATES.
In this chapter we shall give an account of the more commonly occurring mineral phosphates. In Chapter V., where we discussed the position of phosphoric acid in agriculture, it was pointed out that mineral phosphates were very abundant, and that large deposits of them were found in many parts of the world.
Coprolites.
Reference may first be made to the so-called coprolites or phosphatic nodules which have been found in great abundance in the greensand formation, in the crag of the eastern counties, and in the chalk formation of the southern counties. These coprolites are rounded nodules, and are composed of the fossil excrements and remains of ancient animals. They are found in large quantities in Cambridgeshire, and were discovered by Dr Buckland many years ago. The history of their discovery is not a little curious. The manurial properties of road-scrapings in parts of Cambridgeshire were noticed, and on being examined were found to be in part composed of phosphate of lime, derived from phosphatic nodules dug out of the underlying greensand, and used for the purpose of repairing roads. Professor Henslow first drew attention to them at a meeting of the British Association held in Cambridge in 1845, and pointed out that they contained about 60 per cent of phosphate of lime. They were also found in enormous quantities in Suffolk, Norfolk, Bedfordshire, and Essex, and were for a long time largely used in the manufacture of superphosphate, but of late years have not been used to anything like the same extent, owing to the fact that there are richer and cheaper sources of phosphate of lime available. In 1887 about 20,000 tons of coprolites were raised. The richest were those obtained in Cambridge, while those got from Bedfordshire were about the poorest. Deposits have also been found in France and other countries. The average amount of phosphate of lime in English coprolites is between 50 and 60 per cent, while the French contain about 45 per cent.
Canadian Apatite or Phosphorite.
We have already referred in Chapter V. to large deposits of apatite or phosphorite found in Canada. The Canadian mines commenced to be worked about fifteen years ago, and the output now amounts to nearly 25,000 tons per annum.[221] A portion of this goes to the United States; the rest, amounting to about 20,000 tons, being shipped to England, whence it is again exported to Hamburg and other places.[222] It contains from 70 to 80 per cent of phosphate. Deposits are also found at Estremadura in Spain, and in Norway.
Estremadura or Spanish Phosphates.