178 
On Rape-dust. 
both of wlilcli are evolved during- the decomposition of organic 
substances. 
2nd. That rape-dust is most valuable to grain crops : first, 
because all green crops require a large supply of inorganic mat- 
ters,* which rape-dust is deficient in, and derive, by their large 
* From the following table (compiled by Professor Johnston, ' Lec- 
tures on Agricultural Chemistry,' part ii.) it "will be seen that the green 
crops extract from the soil more than double the quantity of inorganic 
matter required by wheat and barley, and that in these inorganic mat- 
ters they take up nine times as much potash, soda, and lime, and Jive 
times as much of the phosphoric and sulphuric acids, as the latter. 
Table of the Inovganic Matters drawn from the Soil by one Course of Crops on the 
Four-course System. 
25 Tons 
of 
Tuinips. 
38 Bushels of 
Barley. 
Seeds. 
25 Bushels of 
Wheat. 
Tutal of 
each 
Element. 
Red 
Clover 
1 Ton. 
Rye 
Grass 
1 Ton. 
Grain. 
Straw. 
Grain. 
Straw. 
115 -.T 
s-r, 
4-5 
45-0 
28-5 
3-3 
om; 
233-0 lbs. 
64-3 
6-8 
1-1 
12-0 
9-0 
3-5 
0-9 
9(i-G" 
2-1 
12-9 
C3-0 
lfi-5 
1-5 
7-2 
149-0 
15-5 
3-6 
I-S 
7-5 
2-0 
1-5 
1-0 
32-9 
2-2 
0-5 
3 1 
0-3 
0-8 
0-4 
2-7 
10-3 
23- (5 
23-6 
90-0 
R-0 
02-0 
G-0 
SC-0 
299-2 
■49 -0 
1-2 
2-8 
10-0 
8-0 
O'S 
1-0 
72-8 
22-4 
4-2 
3-7 
1.5-0 
0-6 
0-0 
5-0 
51-5 
14-5 
0-4 
1-5 
8-0 
0-1 
0-2 
0-9 
2)-() 
382-8 
47-0 
121-7 
168-8 
127'5 
17'8 
105-3 
970-9 
Potash .... 
Soda .... 
Lime . . , . 
Magnesia . . 
Alumina . . . 
Silica . . . . 
Sulpluiric. acid 
Phosplioric do. 
Chlorine . . . 
Total Ashes in 
eacli Crop 
To test this, practically, Boussiugault " determined the per centage 
of carbon in the soil, before the experiment was begun, the weight added 
in the form of manure, the quantity contained in the series of crops 
raised during an entire rotation, until, in the mode of culture adoj)ted, it 
was usual to add manure again ; and lastly, the proportion remaining on 
the soil." {Vide Johnston's Lectures, part i., p. 219.) By this he 
found that in a course of — 
Potatoes — with manure 
Wheat 
Clover 
Wheat 
Oats, 
he had given to the soil, in the manure, 2.513 lbs. of carbon, and ex- 
tracted from it in the crops 7544 lbs., leaving a balance of 5031 11)s. of 
carbon, which must have been extracted from the air, as the soil was left 
in the same condition at the end of the course of crops that it was at the 
commencement. 
From this it will be evident that green crops, by their large surface of 
leaves, &c., possess a great power of attraction for the atmospheric gases. 
— The Author. 
