THE COMPOST HEAP. 77 
began. The result was that nitrates were formed in the interior of 
the heap in large quantity. Eventually the nitrates were extracted 
by water and converted into nitrate of potassium by the addition of 
some potassium salt. 
This method of making saltpeter was discovered before science 
had any idea of the real nature of the process, and it was a practical 
means of utilizing a part of the nitrogen in the organic substances 
derived from animals and plants. Whether it was the most efficient 
means or more useful than the simple compost heap and manure 
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 processes 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 result 
of nitrification of the ammonia which unites with oxygen and pro- 
duces nitric acid. The acid combines with the calcium present in 
the brick- work to form calcium nitrate. The action is an undesirable 
one from the standpoint of the persistence of the walls, since it pro- 
duces 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 on a 
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 
