830 = 564 Influence of Chemical Discoveries on 
effects. In artificial manures for potatoes, the admixture of 
potash-salts to phosphatic and nitrogenous fertilising matters, 
has also been found useful. 
Common salt is used in England principally as an addition 
to manures for mangolds, and, mixed in equal proportions with 
nitrate of soda, as a top-dressing for spring-wheat and barlev. 
It is also useful on light land in dry seasons. 
For loott. largest quantity of all manufactured manures is 
used in England for root-crops. There are many parts of 
England where turnips and Swedes are grown with no other 
manure than mineral superphosphate, containing on an average 
21 to 25 per cent, of soluble phosphate of lime, at the rate of 3 
to 4 cwts. per acre. On cold clay soils, in a fair agricultural 
condition, it has been found that 3 cwts. of such a mineral 
superphosphate will produce at least as heavy a crop of swedes 
and turnips as a manure containing, in addition to soluble 
phosphate of lime, ammonia or nitrogenous organic matter. 
On light land, however, the use of a purely phosphatic manure 
cannot be relied upon for producing a good crop of roots. On 
such land artificial manures are seldom used alone, but usualh 
in conjunction with half a dressing of common dung. Dissolved 
bones, dissolved Peruvian guano, or compound artificial manures 
containing from 2 to 3 per cent, of ammonia, are greatly prefer- 
able to mineral superphosphate as manure for root-crops or 
light land and on loamy soils out of condition. 
Disposal of Sewage and Sewage Manures. — The disposal of town-sewag( 
town sewage, and night-soil is surrounded with many difficulties, and generallj 
entails, more or less, considerable expense upon the inhabitants 
of towns. The sewage question has not made much progres: 
in England since 1860, so far as discovery and invention an 
concerned ; nor does there seem to be much prospect of any nev 
or startling light being thrown upon it in the future. It appear 
from the most recent official reports and investigations of thi 
question, that town-sewage can be disposed of and purified bes 
and cheapest by the process of land irrigation for agricultura 
purposes, where local conditions are favourable to its application 
With rare exceptions, however, sewage irrigation etitails a mor 
or less considerable loss, for which adequate compensatioi 
should be made to the sewage farmer by the town authoritie 
who desire to get rid of sewage, and to have it cleansed am 
rendered innocuous in the most efficient way. 
Effect of soil Experience has shown conclusively, that when foul liquid.* 
and air. such as town-sewage, are passed through a depth of 5 or 6 fet 
of porous and thoroughly drained land, they entirely lose the] 
offensive character ; and that by bringing into practice the pnn 
ciples of downward intermittent filtration, a comparatively smal 
