336 Philosophy of Manures. 



the nitrogen of the air, and forms ammonia. Aided by the 

 pressure of the superincumbent strata, ammonia is thus gene- 

 rated and emitted, like carbonic acid, from fissures in the earth. 

 Sal ammoniac, or muriate of ammonia, is also largely formed, 

 he says, among the lava currents recently ejected on the borders 

 of lakes. Every particle of carbon and ammonia w^hich now 

 exists in plants and animals, he thinks, may have been originally 

 evolved from the interior of our globe ; and being emitted so 

 largely in the neighbourhood of volcanoes will account, he 

 thinks, for the fertility of the lava soils around Naples, as 

 noticed by Dr. Liebig.* Whilst we reason, he says, that ani- 

 mals are the source of nitrogen or ammonia to plants, while 

 these very animals derive their nitrogen from plants, we are 

 reasoning in a vicious circle ; as it brings us to the conclusion 

 that plants must originally have obtained their food exclusively 

 from inorganic matter, there being no animals then. The 

 sources of nitrogen and carbonic acid, at least of their increase 

 to meet the wants of increasing civilisation, are, therefore, the 

 emissions of inorganic matter from the earth. On this head, in 

 the former essay, I stated that nitrogen being partially, to a 

 small extent, soluble in water, the nitrogen of the air might, 

 perhaps, form part of that assimilated in the plant; and Pro- 

 fessor Johnstone, in his first lecture, seems to take the same 

 view of the subject. Boussingault, the professor states, was of 

 opinion that leguminous plants inhaled their nitrogen from 

 the air. 



Professor Daubeny says, 50 gallons of gas tar and 70 lb. of 

 gypsum will produce 60 lb. of sulphate of ammonia, at the cost 

 of only about \d. per lb., not half the price of nitrate of soda; 

 and where the carriage of gypsum is high, vitriol might be 

 substituted. Where the coals contain much sulphur, there is 

 likely to be sulphate, as well as carbonate, of ammonia in the gas 

 tar. The professor, however, seems to be afraid that the mineral 

 acids, especially if they are set free in quantities, and accumu- 

 lated in the plant, will act deleteriously on the vegetable tissue; 

 at all events, as stated in my former essay, the carbonate of 

 ammonia, if washed into the soil in wet weather, or well diluted 

 in water in dry weather (especially when the plants are in a 

 growing state), will not suffer much loss ; but, being dissolved in 

 the vi^ater, which is capable of holding several times its own 

 bulk in solution, will be absorbed by the roots, and thus furnish 

 both carbon and ammonia. The spirits of tar, mixed with sand, 



* Mr. Allen, in his Mineralogy, p. 190., mentions that the hills of the 

 Island of Lipari, of pumice rocks of volcanic origin, are very barren. Some 

 further enquiries on this subject seem still needed : there appears much less 

 alkali in the pumice that forms the hills, than in the obsidian which is found 

 in the valleys. 



