On Rape-dust. 
179 
system of leaves, a greater supply of food from the air than the 
grain crops; secondly, because all plants require a supply of 
nitrogen to perfect their seed,* which nitrogen rape-dust pos- 
sesses in an extremely large proportion. 
3rd. That rape-dust is extremely quick in its effects, and, con- 
sequently, not lasting, because it contains such a large proportion 
of soluble organic matter, and so little of the earthy inorganic 
substances (or, more plainly, so little ashes), that fermentation 
and putrefaction take place immediately ; whence its carbonic 
acid and ammonia are supplied to the roots of the plant in large 
proportions at the commencement of its growth, and, if not taken 
up, escape into the atmosphere. In corroboration of this tendency 
to act quickly, it may be stated that out of 100 parts of rape- 
dust Dr. Madden found 24 7 (or nearly \ of the whole) soluble 
in cold water, while " the first waters were of a pale yellow 
colour, whereas the latter were red ; prov ing that the tendency to 
decomposition was so strong, that it had commenced during the 
process of the analysis." (Vide ' Prize Essays of the Highland 
Society,' June, 1842, p. 529.) 
These, then, are the conclusions which the established prin- 
ciples of vegetable chemistry induce us to come to, from a consi- 
deration of the constituent parts of rape-dust. Practical expe- 
ricnce teaches tis to arrive at the same result. 
Thus I would point to its extensive, and I may almost say 
universal, application as a proof of its general efficiency as a 
fertilizer. f 
* The seed of plants is, in all instances, the most highly azotized 
portion. (Dr. Madden, on Principles of Vegetable Physiology.) Thus 
the grain of wheat (according to Boussingault) contains 2' 13 per cent, 
of nitrogen, and the straw only "20. 
The quantity of nitrogen in the seed varies also, according to the 
quantity of nitrogen contained in, or the ammonia evolved by, the ma- 
nure in the soil. Thus Hermbstaedt found that wheat grown vnthout 
manure gave 9"2 per cent, gluten (containing a large per centage of 
nitrogen) ; 
Wheat with vegetable manure . .9*6 
,, cow-dung . . . 12*0 
„ sheep-dung . . .32*9 
„ night-soil . . .33*14 
It is common to estimate the nutritious quality of flour or grain by its 
amount of gluten. 
■\ I find from authentic sources, that, however general the elBciency of 
rape-dust as a manure may be, I have no right to assert that a know- 
ledge of its value is equally general ; for it is surmised in our Journal 
(vol. iii. p. 210) that the use of rape-dust is only established in Notting- 
hamshire, Yorkshire, and Lincolnshire, while in some of the southern 
counties its use is unknown. Although we have the advantage of the 
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