56 AGRICULTURE. [CH. 



to doubt, but that similar changes take place in the 

 soil under like conditions. In properly constructed 

 compost heaps, especially where some farm-yard 

 manure is present, we have, in fact, a very near ap- 

 proach to what are known as nitre-beds or beds of 

 earth constructed for the production of nitre. 



107. Nitre (or nitrate of potash) is largely used for 

 the manufacture of gunpowder. It happened that in 

 the wars between England and France, in the last cen- 

 tury, the British cruisers kept such a sharp look-out 

 for the trading vessels going to France, that there was 

 often a very great difficulty in getting the nitre they re- 

 quired for their supplies of gunpowder. In 1775 the 

 French Government offered a prize for the best method 

 of producing saltpetre or nitrate of potash in that 

 country. The prize was awarded in 1776 to Mons. 

 Thouvenel, and from that time nitrate of potash has 

 been largely manufactured by what are sometimes 

 known as saltpetre plantations, and in other places as 

 nitre-beds. The general formation of these is very 

 similar. Earth is either intermixed with decaying 

 vegetable and animal matters, or else it is charged with 

 the manure from sheep, and two necessary conditions 

 are thus secured, viz., nitrogenous matter and earth. 

 After a short time chalk or marl is intermixed, and the 

 decomposition which takes place leads to the formation 

 of nitrate of potash. When it is desired to separate the 

 saltpetre it is washed out by water, and the solution is 

 evaporated. Care is taken to protect the nitre beds 

 from rain, which would wash away the nitrate of potash, 

 and the earth is laid up in small heaps so as to secure the 

 full influence of the atmospheric air. In some cases 

 the lime is used in a caustic form, and by its intermix- 

 ture with the soil much of the potash of the soil is 

 liberated, before the caustic lime is converted into the 

 form of carbonate. Soil which has been thus prepared 

 and intermixed with any decaying vegetable or animal 

 matter is admirably adapted for the production of 



