I.] INTRODUCTION OF ARTIFICIAL FERTILISERS 13 



the Rothamstcd cxp)crimcnts were definitely started in 

 1843, a mixture of muriate and sulphate of ammonia 

 became their standard nitrogenous manure. 



The use of mineral phosphates as manure begins 

 with I^wes' sujjerphosphate patents in 1842, although 

 no mineral phosphates were available on a large scale 

 until Henslow's discovery of the coprolitc beds of 

 Cambridgeshire in 1845, soon after which time Lawes 

 and others took them up as material for the manu- 

 facture of superphosphates. Putting aside the various 

 methods adopted for the utilisation of slaughter-house 

 refuse, etc, no further novel manurial substances can be 

 said to have been introduced until the development of 

 the Stassfurt potash deposits, which began about i860, 

 and the discovery of basic slag in 1879, which has been 

 followed in the last few years by various processes for 

 bringing atmospheric nitrogen into a combined form. 



Since the nutrition of the plant is the object with 

 which all manures are employed, it will be necessary 

 at the outset to obtain some knowledge of how a plant 

 feeds under the simplest possible conditions without 

 any of the disturbing effects introduced by the many 

 complex processes going on in the soil. 



If we take any living plant and reduce it to its 

 elements, we find but a small range of substances ; 

 water forms the greatest portion of the plant, the rest 

 is almost wholly composed of compounds of carbon 

 with hydrogen and oxygen, approximately in the 

 proportions which make up water. Of the dry matter 

 of the plant at least half is carbon ; oxygen and hydro- 

 gen constitute most of the remainder; then a certain 

 restricted number of other elements are present in much 

 smaller quantities. Nitrogen constitutes about 2 per 

 cent, of the dry matter ; the other substances, which are 

 found in the ash when the plant is burnt, make up a 



