X XXVIII ROYAL SOCIETY OF CANADA 
In this way the ingenuity of man is providing in goon season, a 
way of escape from the dire results of a nitrogen famine. 
Potash, which as a plant food stands, perhaps, next in importance 
to nitrogen, is widely distributed in nature. Many clay soils contain 
this element in large proportion, in the form of silicate of potash. It is 
found in all fertile soils in considerable proportions, and when the quan- 
tity of this element in the soil has been depleted by over-cropping, it 
may be restored by the application of wood ashes or some other potash 
fertilizer. A good dressing of barn-yard manure, which also contains 
a considerable proportion of potash will help to restore a soil so 
impoverished. 
Most of the potash salts found in commerce or used as fertilisers 
come chiefly from Germany where they exist in practically inexhaustible 
beds, underlying a large section of country. These beds are about a 
thousand feet under the surface and vary in thickness from 50 to 150 
feet. The crude products vary in the percentage of potash they contain. 
Kainit, which is sent into commerce just as it comes from the mine, 
contains from 12 to 20 per cent of potash. The purer potash salts, 
such as muriate and sulphate, are made from the crude products of the 
mine by dissolving, filtering and crystallising. Some idea of the enor- 
mous demand for these potash salts may be formed from the fact that 
the works afford employment for over 9,090 miners and labourers. The 
annual output is said to be about 1,500,000 tons. 
For the third important element, phosphoric acid, there are several 
sources of supply, and the quantities obtainable are large. The bones 
of animals which consist mainly of phosphate of lime was the first form 
in which a phosphatic fertiliser was used on crops. The bones were 
crushed or ground, and the finer they were made the more prompt and 
manifest was the good effect produced. Bone meal was first used about 
the beginning of the 19th century, when its value as a fertiliser for 
turnips was demonstrated. About 1840 superphosphate of lime, made 
by the treatment of bones with sulphuric acid was introduced. This 
compound was much more soluble and speedy in its action on crops. 
Shortly afterwards mineral phosphates were discovered. They were 
found chiefly in America. In Canada there are large deposits, especially 
in Quebec and Ontario, where they occur in crystalline form. The 
mineral phosphate, or apatite, found in Canada contains a larger per- 
centage of phosphoric acid than most of that found elsewhere and was 
mined quite extensively for many years, but more recently other deposits 
have been found where the material is more abundant and more cheaply 
worked and most of the Canadian mines have been closed. In South 
