34. THE MANURE HEAP AND SEWAGE 
cient means or more useful than the simple compost heap and ma- 
nure pile can hardly be stated. 
Saltpeter plantations have gone out of existence since the in- 
troduction of Chilian saltpeter. It is probable that the nitrate 
beds of Chili are the remains of some old inland arms of the sea 
where great growths of seaweeds accumulated which, after the 
drying of the inland sea, were converted into nitrates by the proc- 
esses of decomposition and nitrification due to bacterial action. 
Nitrates are formed upon the walls of closets and stables where 
ammonia fumes are abundant. On such walls may frequently be 
seen a snow-white mass consisting of calcium nitrate. It is the re- 
sult of nitrification of the ammonia which unites with oxygen and 
produces nitric acid. The acid combines with the calcium present 
in the brick-work to form calcium nitrate. The action is an unde- 
sirable one from the standpoint of the persistence of the walls, since 
it produces a corroding action tending to weaken the structure. 
It may be readily prevented by sprinkling the walls with a strong 
solution of some powerful antiseptic, such as formalin or corrosive 
sublimate. 
THE COMPOST HEAP 
It is evident that in a compost heap there must be going ona 
series of similar bacterial transformations. By proper means the 
farmer may make use in his soil of almost any organic material 
which contains nitrogen or the minerals needed for his crops. 
Vegetable tissues of all sorts contain more or less nitrogen and may 
readily be brought under the influence of the bacteria which are 
able to reduce them to plant foods. A valuable source of such 
material may be obtained from seaweeds, if they areathand. In- 
deed, any abundant vegetable substances may thus be heaped into 
a mass, and, if moistened sufficiently by rains, the bacteria will be 
sure to work within it, gradually transforming the nitrogens, and 
converting them finally into nitrates for plant food. Into his 
garbage heap, then, the farmer may throw all sorts of organic 
