The Phosphates used in Agriculture. 27 5 



farmer, not only immense quantities of ox bones have been im- 

 ported 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 carbonic acid, 

 and other vegetable acids of the soil, and cannot penetrate into 

 the tissues of plants until it is so dissolved. In order, there- 

 fore, to furnish plants with phosphate of lime in a soluble 

 state, Liebig proposed that bones or other phosphates should be 

 treated with sulphuric acid. Hence arose the manufacture of 

 superphosphate or soluble phosphate of lime, which has, of late 

 years, taken such extension in England. It is to this manufac- 

 ture 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 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 agricultural chemistry, making known the 

 principle of the manufacture 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 abun- 

 dant in many parts of the globe. In certain tropical regions 

 (Peru, Chinca Isles, etc.), 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 phosphate of lime. But 

 in localities which are frequently visited by hurricanes and much 

 rain, the organic constituents and salts of ammonia are washed 

 out, and the mineral constituents increase in proportion : tho 

 guano becomes less valuable as a manure, by loss of its ammo- 

 niacal compounds, but constitutes a plentiful source of phosphate 



vol. v. — NO. iv. u 



