7o 
The conversion of the nitrogenous constituents of the soil 
into nitrates assimilable by plants is known as nitrifi- 
cation. In order to bring about this little understood 
process three conditions are necessary, viz: the presence of 
bacteria, a supply of Oxygen, and a salifiable base such as Lime, 
Soda, or Potash. Nitrification takes place under favorable cir- 
cumstances in all fertile soils, and as the bacteria are most active 
at a temperature of from 75 to 100 degrees, F., it is between these 
thermal points, that plant growth is most vigorous. At tempera- 
tures much below that indicated the work of the bacteria is re- 
tarded and at a certain degree of coldness their operation ceases. 
The economic use, from the point of plant life of these beneficial 
organisms, therefore, is their conversion of the nitrogenous or- 
ganic matter and ammonia compounds of the soil and. to a less 
extent of the air, into soluble plant food'. This is effected by 
combination with such bases as Lime and Potash with which 
Nitrates are formed. From these latter compounds plants derive 
most of their nitrogen, and in order to support plant life, it is 
necessary that such soluble nitrates be present. 
When the natural supply of nitrates in the soil becomes ex- 
hausted, it is necessary that these be renewed artificially. This 
opens up the important subject of plant fertilization, which is 
every year forcing itself more and more to the notice of agri- 
culturists. 3 As the available supply of nitrates is restricted, the 
question of the continued fertilization of the soil is an exceeding- 
ly urgent one. With regard to the supply of animal manure, 
(the use of which as a supply of plant nitrogen has obtained' in 
all ages, although it is only during the last century that the rea- 
son of its beneficial action was understood) the production is 
diminishing rather than increasing. Moreover with more en- 
lightened knowledge of hygiene, even if this fertilizer were to 
become available in sufficient quantities, it is questionable 
whether for this reason alone its general use for agricultural 
crops would be adopted. 
Among the nitrogenous chemical manures, Sulphate of Am- 
monia is important. This fertilizer is produced by the destruc- 
tive distillation of coal and shale, and is a by-product in the 
manufacture of gas. Although its manufacture is extending it 
3 An additional vagary on the part of the element Nitrogen also tends 
to emphasize the importance of the diminishing available supply of this 
important vegetable food, for it does not follow the natural cycle pur- 
sued by most other substances in their appropriation by the organic 
world. As a rule the constituents of the primitive rocks crumble into 
soil and after assimilation by vegetables and animals are returned 
again to the soil. With regard to Nitrogen, however, such a cycle is 
not completed, for this element, instead of returning to the soil passes 
off into the atmosphere. There is therefore a continual process in 
operation for the liberaton of Nitrogen from combination with other 
elements, and each generation of life depletes the earth of its supply and 
diminishes the potentiality of our planet for sustaining organic life. 
