PHOSPHATES USED IN AGRICULTURE. 
635 
and waste places, at butchers^ establishments, &c. Since the 
manufacture of superphosphate of lime began for the use of the 
farmer, not only immense quantities of ox bones have been 
imported yearly into England from South America and other 
countries, but a large number of natural deposits of phosphate 
of lime have been discovered and utilized without delay in 
the interests of agriculture and manufactures. It was shown 
by Liebig that it was of little use to supply ground bones to 
the soil in order to obtain a rapid result, for the bone earth 
takes a long time to become soluble by the action of the car¬ 
bonic acid, and other vegetable acids of the soil, and cannot 
penetrate into the tissues of plants until it is so dissolved. In 
order, therefore, to furnish plants with phosphate of lime in 
a soluble state, Liebig proposed that bones or other phos¬ 
phates should be treated with sulphuric acid. Hence arose 
the manufacture of superphosphate or soluble phosphate of 
lime, w T hich has, of late years, taken such extension in 
England. It is to this manufacture principally that is owing 
the enormous importations of phosphate of lime in various 
forms which arrive in Great Britain from all parts of the globe. 
It was probably the introduction of guano from South 
America that brought certain practical minds to consider 
more attentively the best means of restoring the fertility of 
exhausted soils, and of keeping up the fertility of those not 
yet exhausted. This extraordinary and powerful manure, the 
enormous supplies of which appear to have been stored up 
by Providence for the actual wants of agriculture, as the 
endless supplies of coal have accumulated in bygone ages to 
supply the wants of our manufactories, was brought to Europe 
in 1804, by Alexander von Humboldt, as a scientific curiosity . 
Its valuable nature was not entirely appreciated by the public 
at large until about 1838, when large quantities of it began to 
be imported into England as a manure. Two years later 
(1840), Liebig brought out his well-known work on agri¬ 
cultural chemistry, making known the principle of the manu¬ 
facture of superphosphate of lime, and in 1842 Mr. Lawes 
began to manufacture this superphosphate manure. 
Guano being, as is well known, the accumulated excrement 
of sea-fowl (and, consequently, having the same composition 
as the excrements of pigeons and other domestic birds), is 
abundant in many parts of the globe. In certain tropical 
regions (Peru, Chinca Isles, &c.), where it never rains, this 
guano is very rich in urate, oxalate, and phosphate of 
ammonia, besides containing about 22 or 23 per cent, of phos¬ 
phate of lime. But in localities which are frequently visited 
by hurricanes and much rain, the organic constituents and 
