Chemical Changes in the Fcnnentalion of Dimcj. 343 
" Wood and mineral coal are always accompanied by iron pyrites (sulplniret 
of iron) or /,inc blende (sulphuret of zinc), which minerals are still formed 
from salts of sulphuric acid with iron or zinc during the laitrefaction of all 
vegetable matter." — Ih., p. 350. 
That this change is not dependent upon close vessels or deficiency 
of oxygen is proved by the case of the broccoli field above men- 
tioned and by that of heaps of decaying nightsoil.* 
The formation of tliis compound in our manure heaps is doubly 
wasteful. It I'obs the farm of sulphur which ought to be in the 
most suitable form for plant food inasmuch as it has once formed 
part of living plants ; and by its union with the valuable am- 
monia it actually assists its escape. It is surely matter of no 
small moment to prevent the formation of sulphuretted hydrogen 
altogether if possible ; and if not then the aim should be to arrest 
and oxidize it.j 
In regard to the inorganic part of manure general opinion is 
pretty accurately expressed by the author who says " the in- 
organic salts of the urine and of the solid excrements are not 
essentially altered by putrefaction." But yet some well-known 
statements ill accord with tliis. Dr. Stenhouse found fermenting 
human urine treated with milk of lime to yield a precipitate 
which when dried at 212° F. contained 40 per cent, of phos- 
phoric acid and organic matter including about 1 per cent, of 
ammonia. Johnston, p. 189. 
In the table quoted in the Appendix we find 180 parts of the 
salts of cow's urine passed from a soluble to an insoluble condi- 
tion during a month's fermentation. Now whether we take the 
analysis of Berzelius which assigns the phosphoric acid of 
* The reader will bear in mind one or two illustrative facts of daily occurrence. 
A silver spoon in an egg, or a dish of peas, becomes blackened by the formation 
of sulphuret of silver upon its surface. The same thing occurs when a silver 
spoon is boiled in a saucepan in which soup is being made in the ordinary way. I 
recently met with a case in which the gluten of wheat had become so altered by 
decomposition, that when the flour made from it was boiled as food for a child, it 
turned the silver spoon with which it was stirred quite black. 
t The following, from Turner's ' Chemistry,' p. 691-2, ed. 8, hints at what 
I have endeavoured to develop : — " In putrefaction the access of air is necessary, 
at all events to commence tlie process ; and here the elements of the ferment or 
exciting body probably do contribute, with those of the putrefying body, to form 
some of the new products, which are very varied. This process, although essen- 
tially the same as fermentation, is commonly characterized by the offensive smell 
of some of the products, among which are ammonia, sulj>huretted hydrogen, and 
perhaps phosphiiretted hijdrogcii, since those bodies which are prone to putrefaction 
are commonly compounds containing nitrogen, sulphur, and phosphorus." The 
writer has not stated his view as to the form of existence of this sulphur and 
phosphorus, but as he subsequently doubts and appears to disbelieve the presence 
of uiioxidized phosphorus in albumen (p. 1266), we must suppose he considers 
them as combined with oxygen. 
