Lecture on Town Sewage. 
4G5 
a small portion of the soil ; and in ordinary good farm practice, we 
endeavour to keep the manure, be U natural or artificial, as near to 
the surface as possible. The value of a manure, then, depends quite 
as much on the facility with which it can be applied, as upon the 
amount of the fertilising materials which it contains. Concentrated 
manures, s\ich as superphosphate of lime or giiano, are, for this 
reason, of the greatest utility on most soils ; for most soils are rich 
in plant food, but the}' do not contain sufficient to meet the require- 
ments of the plant in its early stages of growth. Our ordinary 
farm routine is to manure principally a small portion of the soil, 
just to provide for this requirement. 
On a sandy soil, it is true, we must put in everything that is 
to go afterwards into the plant ; and it is on such soils that sewage 
may be used with very great advantage, and that bulky manures, 
like farmyard manures, will alwaj's be applied with as great, or 
even greater advantage than most artificial manures. 
But on most other soils, and more especially those which contain 
a sufficient amount of clay, we have both a great abundance of 
minerals and also a considerable amount of matter capable of yield- 
ing ammonia in decomposition, as the following analyses show : — 
Analyses of Three Clay Soils. 
Water driven off at 212° F 
Organic matter and water of combination 
Oxides of iron 
Oxides of alumina 
Carbonate of lime 
Lime 
Magnesia 
Potash 
Soda 
Phosphoric acid 
Soluble silica 
Insoluble silicates (fine clay) 
Chlorine and sulphuric acid 
Carbonic acid and loss 
•53 
•62 
•07 
•74 
•60 
•26 
•22 
•38 
•45 
84-10 
traces 
•03 
100-00 
II. 
5- 38 
6- 82 
6^67 
1^44 
•92 
1-48 
1^08 
•51 
III. 
72-83 
traces 
2-87 
100-00 
Moreover, clay itself possesses in a high degree the power of 
absorbing ammonia from the atmosphere. Still, however A'aluable 
may be the stores of food for plants which those soils contain, they 
do not appear to have enough in an available form for the young 
plant. We therefore apply a concentrated manure just to start the 
plant, and when this is accomplished, the manure has fulfilled its 
purpose, though it cannot add much to the general fertility of the 
land. 
The maximum effect which such concentrated manure is capable 
of producing on a soil is soon reached. 3 cwt. of superphosphate of 
lime is found to answer quite as well as 6, 7, or 8 cwt. per acre. 
VOL. XXIII. 2 H 
