634 
PHOSPHATES USED IN AGRICULTURE. 
than that of any other country; consequently, the soil here 
is caused to do its utmost, and the effects of exhaustion have 
been sooner and more keenly felt. Although scientific agri¬ 
culture, as regards its diffusion among the people, is still in a 
deplorable state on the continent of Europe, as may be seen 
by glancing from time to time at the periodical literature of 
Belgium, France, Germany, and Italy, the time will certainly 
come when the art of manufacturing and applying manures of 
all descriptions will be as actively pursued in these countries 
as in England at the present day. 
Three of the more important ingredients wffiich soils lose 
by cultivation, and which it is necessary to restore to them in 
greater or smaller quantities, are potash, nitrogen, and phos¬ 
phate of lime. Nature herself supplies these substances to 
the soil in various ways, and in quantity sufficient for the 
growth of wild plants. Thus, potash is washed into the soil 
by the rain-water3 which flow over granitic and felspar rocks, 
so that every little stream contains some of it; nitrogen, in 
the form of ammonia, is constantly present in the atmosphere, 
and phosphate of lime is very widely distributed over the 
globe. Moreover, the excrements of animals contain all three. 
Another ingredient very essential to vegetable life is carbonic 
acid, of which there is so large a supply in the atmosphere, 
in the streams, and rocks of the globe, that it is rarely neces¬ 
sary to supply it artificially to our cultivated crops. 
I have said that nature supplies a sufficiency of these more 
important constituents of the fertile soil, to ensure the growth 
and luxuriance of wild plants. But in agriculture we are 
dealing with an artificial state of things, and the natural 
supply no longer suffices to maintain fertility in our culti¬ 
vated soils. In our present system of manuring, potash is 
supplied by farm-yard manure, sometimes by wood-ashes, 
and by manures made by drying the excrements of animals 
(sewage, &c.). The first and last of these supply also am¬ 
monia and phosphates. Our chief sources of nitrogen are 
Peruvian guano, nitrate of soda, and sulphate of ammonia 
(from the gas-works). The first of these supplies, at the 
same time, phosphate of lime, and the last is sometimes 
introduced into artificial manures, such as the ammoniacal 
superphosphates. 
Our sources of phosphate of lime are most numerous, and 
it is to these alone that I shall devote the present paper. A 
few years ago, all the phosphorus used for the manufacture 
of lucifer matches was extracted from bones, the phosphate of 
lime used in the various manufactories was likewise obtained 
from bones. These were principally collected in the streets 
