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._
Large deposits of phosphate have long been known to exist at Estremadura
in Spain, and the mines at Caceres have been worked on a large scale for
seventeen years, and about half a million tons have been raised. In 1882
the imports into this country amounted to over 56,000 tons; but latterly
they have only been about a fourth of this amount. Dr Dauberry visited
the deposits in 1843, and wrote a most interesting account of them. They
do not seem, however, to have been imported for purposes of
superphosphate manufacture till a number of years afterwards. Of
Estremadura phosphate there are three classes, containing respectively
50, 60, and 70 per cent of phosphate of lime, the lowest quality being
the commonest.[223]
_Norwegian Apatite._
This apatite has ceased to be imported of late years, owing to a duty on
exportation.
_Charleston or South Carolina Phosphate._
For a number of years these deposits have formed the chief source of
phosphate of lime used in the manufacture of mineral superphosphates in
this country (in fact they have furnished two-thirds of our phosphate
supply during recent years). Discovered twenty-five years ago, some four
to five million tons have already been shipped. About half a million
tons were raised in 1886 from these mines, which are the most abundant
in the world. There are two kinds--the so-called "land" and "river"
phosphates. The former contains more oxide of iron and alumina, and is
therefore less pure than the latter, in which the iron and alumina do
not exceed 2 per cent. The river phosphate is dredged from the Bull,
Coosaw, and Beaufort rivers. Of phosphate of lime it contains from 50 to
60 per cent. It is generally sold in three grades--50 to 52 per cent, 55
to 56 per cent, and 58 to 60 per cent of phosphate of lime. It will thus
be seen to be incapable of producing very high-class superphosphates
--_i.e._, containing more than 30 per cent "soluble" phosphate.
This point will be more intelligible when we describe the manufacture of
superphosphate. The demand for these phosphates in the United States has
increased enormously in recent years, owing to the increase in the
quantity of manure used.
_Belgian Phosphate._
Another very important source of mineral phosphates are deposits
discovered some years ago in Belgium near Mons. These phosphates are of
different qualities, and are found, some in layers near the surface in
pockets forming the richest class, and containing from 45 to 65 per cent
of phosphate, and some in the form of a friable phosphatic rock, the
so-called _craie-grise_ (phosphatic chalk), containing from 25 to 35 per
cent of phosphate of lime. The higher quality of Belgian phosphate is
pretty well exhausted, and it is the second class that forms the bulk of
the ordinary Belgian phosphate at present exported. The commercial
article contains about 35 to 40 per cent of phosphate, and about 45 per
cent of carbonate of lime. The fact of its poor quality, together with
the large percentage of carbonate of lime it contains, renders its
adoption alone in the manufacture of superphosphate unsuitable. Attempts
have been made to get rid of a portion of this carbonate of lime and to
raise the percentage of phosphate. For this purpose the phosphate has
been calcined, but this was soon found to be a great mistake. Other
means have been adopted, with the result that the percentage has been
increased to 50 per cent. It is consequently used in small quantities
as a drier, for which it is peculiarly suited on account of its
carbonaceous nature, along with the higher-class phosphates. In the year
1886 about 145,000 tons of this phosphate were raised, of which about
45,000 tons were imported into the United Kingdom.
_Somme Phosphate._
Still more recently a discovery of phosphate deposits has been made in
the Somme and Pas de Calais departments in the north of France,
adjoining, and similar in character to, the Belgian deposits. The only
difference between Belgian and French phosphates is, that the latter is
of a higher quality, and contains from 50 to 80 per cent of phosphate of
lime. A very large demand for these phosphates sprang up, and in 1888,
although they had only been worked for some two years, no less than
150,000 tons had been raised, of which about one-half contained from 70
to upwards of 75 per cent. There are four grades in the market,
containing 55 to 60, 60 to 65, 70 to 75, and 75 to 80 per cent of
phosphate of lime. The highest quality furnishes the chief material for
the manufacture of high-grade superphosphates.
_Florida Phosphate._[224]
During the last few years large quantities of phosphates have been
imported from Florida. These are of different qualities, the land rocks
now imported containing from 70 to 80 per cent of phosphate of lime, and
the river phosphate about 60 per cent. The latter class are similar in
composition to the best South Carolina river-phosphates, which they much
resemble.
_Lahn Phosphate._
Phosphate deposits were found at Nassau in Germany in 1864; but as the
phosphate contained a considerable proportion of iron and alumina, they
are not used in this country now, although they are in Germany for
double superphosphate manufacture.
_Bordeaux or French Phosphate._
Similar in quality to Lahn phosphate is that obtained in the
neighbourhood of Bordeaux.
_Algerian Phosphate._
Excellent phosphates are now being sent from Algeria--some cargoes being
as rich as 70 per cent.
_Crust Guanos._
We have already referred to the guanos in the chapter on Guano. They are
also known under the name of Caribbean phosphates, and come from the
West India Islands. The chief kinds are Aruba, Curacao, Sombrero, and
Navassa, the Great Cayman, Redonda, and Alta Vela. Most of them are of
high quality, containing from 60 to 80 per cent of phosphate, and are
thus suited for the manufacture of high-class superphosphates. Some of
them, however, contain a considerable proportion of iron and alumina,
and are not suitable for this purpose. The Redonda and Alta Vela
phosphates consist chiefly of phosphate of alumina.
_Value of Mineral Phosphates as a Manure._
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).
THE FOLLOWING TABLE SHOWS THE IMPORTS OF PHOSPHATES INTO THE UNITED
KINGDOM, AND THE COUNTRIES OF PRODUCTION, DURING THE YEARS 1885-92.
-----------------------+---------+---------+---------+---------+---------+
| 1885. | 1886. | 1887. | 1888. | 1889. |
-----------------------+---------+---------+---------+---------+---------+
| Tons. | Tons. | Tons. | Tons. | Tons. |
United States | 138,844 | 144,623 | 165,275 | 111,369 | 122,554 |
Canada | 21,484 | 18,069 | 19,194 | 12,423 | 23,297 |
Dutch West Indies | | | | | |
(Curacao, Aruba) | 11,588 | 12,581 | 9,505 | 10,736 | 14,730 |
British West Indies | | | | | |
(Sombrero, &c.) | 7,727 | 3,351 | 6,451 | 11,010 | 1,880 |
Spain and Portugal | 19,282 | 5,825 | 15,612 | 6,978 | 1,326 |
Belgium | 35,405 | 31,551 | 45,322 | 54,261 | 64,643 |
Holland | 865 | 2,194 | 4,778 | 4,137 | 2,270 |
France | 2,276 | 1,503 | 11,140 | 39,059 | 65,490 |
Australia | - | 200 | 350 | - | 1,250 |
Germany | 704 | - | - | - | - |
Hayti (San Domingo) | - | 2,175 | 3,044 | 6,238 | 4,094 |
Brazil | - | - | 1,200 | - | - |
Venezuela and Guiana | - | - | 405 | - | - |
Norway | - | - | - | - | - |
Other countries | 397 | 1,039 | 1,139 | 1,675 | 390 |
| | | | | |
*Florida phosphate. | - | - | - | - | - |
Carolina phosphate. | - | - | - | - | - |
-----------------------+---------+---------+---------+---------+---------+
-----------------------+---------+----------+----------
| 1890. | 1891. | 1892.
-----------------------+---------+----------+----------
| Tons. | Tons. | Tons.
United States | 177,283 | *131,084 | *201,465
Canada | 21,089 | 15,918 | 7,814
Dutch West Indies | | |
(Curacao, Aruba) | 14,763 | 8,851 | 6,648
British West Indies | | |
(Sombrero, &c.) | 3,970 | 1,960 | 2,473
Spain and Portugal | - | 320 | 971
Belgium | 82,096 | 70,723 | 65,079
Holland | 2,428 | 3,434 | 6,627
France | 35,659 | 18,325 | 18,239
Australia | - | - | -
Germany | - | - | -
Hayti (San Domingo) | 992 | 1,639 | 2,965
Brazil | - | - | -
Venezuela and Guiana | - | 540 | -
Norway | 4,151 | 1,495 | 305
Other countries | 1,070 | 1,483 | 1,594
| | |
*Florida phosphate. | - | 35,203 | 66,327
Carolina phosphate. | - | 96,881 | 135,138
-----------------------+---------+----------+----------