336 



Saltpetre and Plaster of Paris. 



Vol. Vllf. 



For the Farmers' Cabinet. 

 Saltpetre and Plaster of Paris. 



Mr. Editor, — In order to ascertain what 

 manures are best for land, it is necessary to 

 consider the objects of agriculture. Those 

 objects are principally to produce grain and 

 grass; which productions are used for the 

 food of man and animals. Food and cloth- 

 ing for man are the ulterior objects of farm- 

 ing. I will, for the present, confine myself 

 to the former. What are the elements of 

 the food of man ? Dr. Liebig has analyzed 

 wheat flour, and found it to consist of starch, 

 gluten and magnesia; beef and other ani- 

 mal substances consist in great part of nitro- 

 gen. The gluten of wheat is the only part 

 of it which enters into the formation of flesh, 

 and supplies the human system with nitro- 

 gen. Nitrogen being the principal constitu- 

 ent of the flesh of animals, and also of flour, 

 makes those substances the fittest and strong- 

 est food for man. As flesh contains so much 

 nitrogen, it follows that the food of animals, 

 viz., grain and plants, should contain nitro- 

 gen ; and in corroboration of that inference, 

 Dr. Liebig says that nitrogen is an invari- 

 able constituent of plants, — and that corn, 

 grass, and all plants without exception, con- 

 tain nitrogen. And in turn, as plants and 

 grain contain nitrogen, it is important tliat 

 the manure intended for the food of plants, 

 should contain all the nitrogen possible; and 

 that it should be retained in any manure 

 that the farmer has, and not suffered to rise 

 from it in the form of gas, and be blown 

 away by the wind. 



But what is nitrogen, if it is so importanf? 

 It is a simple substance in the form of a gas; 

 it constitutes about four-fifths of the atmos- 

 phere ; it rises from putrefying animal and 

 vegetable substances, also from animal ma- 

 nures, and especially from the urine of men 

 and horses; it rises from these substance? 

 in the form of ammonia — which is composed 

 of nitrogen and hydrogen — which unite 

 with the carbonic acid, which also exists in 

 the atmosphere generally, and form carbo- 

 nate of ammonia. Nitrogen is also a princi- 

 pal constituent of saltpetre, in the language 

 of chemistry, called nitre. Those who have 

 paid some attention to chemistry, know very 

 well what nitrogen is. We farmers must 

 have recourse to chemistry; we know no- 

 thing about manures except as to their ap- 

 parent effects; we do not know, without the 

 aid of chemistry, which of the elements or 

 simple substances of which that manure is 

 composed, produces those effects. 



Dr. Liebig says, "This ammonia has not 

 been produced by the animal organism, it 



existed before the creation of human beings, 

 — it is a part, a primary constituent, of the 

 globe itself" It is undoubtedly not only an 

 mdispensable manure, but a cheap one. The 

 nitrogen of decaying animals and vegetables 

 rises into the atmosphere in the form of am- 

 monia, and whenever it rains, this ammonia 

 is brought from the atmosphere to the sur- 

 face of the earth, and is as constantly re- 

 placed by the putrefaction of animal and 

 vegetable matters. A part only of the car- 

 bonate of ammonia, which is conveyed by 

 rain to the soil, is received by plants, be- 

 cause a certain quantity of it is volatilized 

 with the vapour of water; only that portion 

 of it can be assimilated or taken up by the 

 roots, which sinks deeply into the soil, or 

 which is conveyed directly to the leaves by 

 dew, or is absorbed from the air along with 

 the carbonic acid. 



Saltpetre is made from decayed vegetable 

 and animal matter, combined with potash, 

 proving one constituent of saltpetre identical 

 with nitrogen. Ammonia is an extremely 

 pungent gas, and is manufactured from 

 horns, bones, parings of hides, and other 

 animal substances. Liquid ammonia is 

 known also by the name of spirit of harts- 

 horne. As ammonia and saltpetre are 

 manufactured from vegetable and animal 

 substances, it follows that nitrogen — the 

 principal constituent of both — must have 

 been food of both plants and animals. 



The only remaining question can be, how 

 is such a volatile substance to be fixed in 

 the soil, and kept in the possession of the 

 agriculturist. 



Mr. Liebig has also decided this matter; 

 he says, "The evident influence of gypsum 

 upon the growth of grasses — the striking 

 fertility and luxuriance of a meadow upon 

 which it is strewed — depend principally 

 upon its fixing in the soil the ammonia of 

 the atmosphere, which would otherwise be 

 volatilized, with the water which evaporates. 

 The carbonate of ammonia contained in rain 

 water, is decomposed by gypsum in precisely 

 the same manner as in the manufacture of 

 sal-ammoniac. Soluble sulphate of ammo- 

 nia and carbonate of lime are formed ; and 

 this salt of ammonia possessing no volatility 

 is consequently retained in the soil. All 

 the gypsum gradually disappears, but its 

 action upon the carbonate of ammonia con- 

 tinues as long as a trace of it exists." 



Again, he says, "It is quite evident there- 

 fore, that the common view concerning the 

 influence of certain salts upon the growth 

 of plants, evinces only ignorance of its cause. 

 The action of gypsum or chloride of calcium, 

 really consists in their giving a fixed condi- 

 tion to the nitrogen, or ammonia which is 



