While it is commonly regarded as unadvisable to use mineral phosphates directly as phosphatic manures, it may well be questioned how far such an opinion is warranted by actual experience. Professor Jamieson of Aberdeen, in his interesting and valuable experiments, has drawn attention to the fact that coprolites in a fine state of division are an extremely valuable source of phosphoric acid for crops, and are a more quickly available source than is commonly supposed. Experiments conducted elsewhere with ground coprolites and other mineral phosphates corroborate Professor Jamieson's conclusions. The successful use of Thomas-phosphate has drawn attention to the possibility of profitably applying undissolved mineral phosphate to the soil; and no doubt the practice may in future years be increased. At present, however, with the exception of Thomas-phosphate, mineral phosphates alone are used for conversion into superphosphate.
FOOTNOTES:
[221] Since the discovery of the Florida deposits of phosphate, the working of the Canadian mines has been practically abandoned.
[222] See Appendix, p. 381.
[223] These phosphates are now no longer worked.
[224] These deposits were discovered a few years ago; and as they are of considerable extent and high quality, have entirely revolutionised the phosphate market. About 300,000 tons are now annually raised in Florida.
APPENDIX TO CHAPTER XII.
NOTE (p. 375).