Chemical Clianr/es in the Fermentation of Dimg. 333 
VI. The account of these experiments would hardly be com- 
plete unless it were extended to note the value of green vegetable 
matter as a manure, and a peculiarity of its fermentation which 
seems to have been doubted or denied. Ploughing in a green 
crop is thought to enrich the land in carbon by the fermentation 
in the soil of wliat is ploughed under. Gathering green vegetable 
matter into heaps is regarded very much in the light of forming 
" a carbonaceous residue of decayed plants." JNIr. Stephens has 
some strong remarks of this kind under the head of " composts," 
and Prof. Johnston appears to lean to the same view. The 
latter gentleman has however one passage which it is impossible 
to pass, as a very large number of my own observations are en- 
tirely opposed to it. He says " vegetable substances in general 
do not decay so rapidly, and emit iio odour of ammonia icJicn fer- 
meriting." {^Elements of Agricultural Chemistry, p. 205.) The 
words " in general " are in italics, and are clearly meant in some 
measure to qualify what is stated. But, if the passage mean any 
thing, its signification is that with very few exceptions the fact is 
as stated. 
Having considerable doubt of the fact I resolved to test it 
practically, and have had collections of green vegetable matter 
made whenever possible. It has been placed in small heaps 
such as a barrowful, and in large ones of 2 or 3 cartloads, and 
comprises grass, cabbage, radishes, and weeds of every kind 
grown in the neighbourhood. I have tested more than fifty heaps 
composed chiefly of different weeds and in no instance have I 
failed in getting turmeric paper strongly browned when lield in 
the vapour given off by the decomposing substances. The " odour 
of ammonia" was certainly not perceptible at a distance from 
my one or two barrowsful of weeds fermented in the open air, 
but neither would it have been from an equal quantity of ordinary 
manure under the same circumstances. It was however dis- 
tinctly and easily perceptible if the nose were placed close to 
that portion of the heap from which a forkful had just been 
taken, and I am induced to suspect that the want of this precau- 
tion led to the statement I have quoted from that justly high 
authority Prof. Johnston.* 
* Small Heaps of Weeds. — I have this year had made from forty to fifty small heaps 
of -weeds of various liinds with a view to ascertain whether from a bushfl to a 
barrowful would alaays give off scmsible ammonia. In every case I detected it by 
smell and by turmeric. 
Lfiiye Weed Heap. — To remove this subject from the domain of nice chemical 
investigation or delicate manipulation and bring it fully within the cognizance of 
the illiterate I collected between six and seven cartloads of weeds and placed them 
to rot upon a hardly-trodden unabsorbent bottom. The unabsorbent character of 
the base is so essential to perfect success in the experiment, that I would advise 
those who repeat it to select, if possible, a place which has been puddled. 
The weeds were all pulled by hand from among onion crops. They were in full 
VOL. XVI. z 
