THE WORK OF PROFESSOR LOUIS GRAN'DEAU. 223 



unwilling to admit that soil humus could play any part in such 

 a complex phenomenon as plant nutrition. As is generally the 

 case, the truth lay between the extreme views of the opposing 

 schools, and to Grandeau belongs the merit cf having clearly 

 demonstrated that the fertility of a soil depends largely on the 

 proportion of "black matter" which it contains, i.e. both on the 

 organic and mineral constituents. 



Grandeau commenced his work by examining three types 

 of soil, the fertility of which was well known and widely different. 



1. The black soils of Russia (tchernozeii), the fertility of 



which is proverbial, and which, even without manur- 

 ing, yield crops far superior to those of many soils 

 which are regularly manured. 



2. The soil of Lorraine, a clay soil of fairly good fertility 



but requiring regular manuring. 



3. A sterile unmanured peaty soil (Nancy). 



If only the chemical composition of the soils was considered, 

 it was found that soils of medium fertility contained a higher 

 percentage of nitrogen, phosphoric acid, potash and lime, 

 respectively, than the rich black soil of Russia. This led 

 Grandeau to investigate more thoroughly the composition of the 

 organic matter of the soil. Part of the organic matter is soluble 

 in water and acids, but insoluble in alkalies, and is of little use 

 to the plant. A second portion of the organic matter, on the 

 other hand, is insoluble in water and acids but dissolves in 

 alkalies. This mixture of substances, which make up the 

 greater part of the soil humus, is the "black matter" of 

 Grandeau. Before this time, chemists had chiefly been 

 concerned with the ultimate composition of the " black matter," 

 i.e. with the percentages of carbon, hydrogen, oxygen and 

 nitrogen, etc., which it contained. Grandeau, on the other 

 hand, devoted himself to the investigation of its mineral 

 constituents in the hope of finding the key to the problem. On 

 evaporating to dryness the dark-coloured solution of humic 

 matter obtained by successive extractions of the soil with dilute 

 ammonia, a black, shining, brittle residue is obtained, which 

 is insoluble in water, alcohol and acids, and soluble only in 

 alkalies. This he terms the " black matter." On incineration 

 this leaves a reddish ash, the darkness of the colour depending 

 on the amount of iron present. The mineral residue so obtained 

 contains phosphate of iron, lime, magnesia, silica and potash. 



