tter. Bone-black or bone-char is an article which is prepared
in enormous quantities for use in sugar-refineries, where it is used in
the purification of sugar. After use it may be renovated by submitting
it to heat; but as this process gradually lessens the percentage of
carbon it contains, after a certain period it becomes too poor in this
substance for efficiently acting as a filter. When this takes place it
is technically known as spent char, and is used for the manufacture of
superphosphates. Spent char is a highly phosphatic substance, being very
little poorer than bone-ash, and containing about 70 per cent of
phosphate of lime.[220]

FOOTNOTES:

[216] It is only fair to Liebig to say that when he wrote these words
the practically boundless supply of mineral phosphates which we now know
to exist in many parts of the world was little dreamt of.

[217] See Appendix, Note I., p. 371.

[218] See Appendix, Note II., p. 371.

[219] See Appendix, Note III., p. 372.

[220] See Appendix, Note IV., p. 372.

APPENDIX TO CHAPTER XI.

NOTE I. (p. 364).

The following analysis will serve to show the composition of
bone-meal:--

Moisture 10.43
*Organic matter 32.30
Phosphate of lime 48.40
Carbonate of lime, magnesia, &c. 7.20
Insoluble siliceous matter 1.67
------
100.00
------
*Containing:--
Nitrogen 3.71
Equal to ammonia 4.51

NOTE II. (p. 368).

COMPOSITION OF DISSOLVED BONES.

The accompanying analysis may be taken as representing the average
composition of dissolved bones:--

Moisture 10.10
*Organic matter and water of combination 29.34
Monobasic phosphate of lime 11.23
(Equal to tricalcic phosphate rendered "soluble" 17.58)
Phosphate soluble in ammonium citrate 14.02
Insoluble phosphate of lime 1.88
Calcium sulphate, magnesia, alkalies, &c. 30.23
Sand 3.20
------
100.00
------
*Containing:--
Nitrogen