OF MANURE. 



69 



powder, and moistened bones generate heat 

 and enter into putrefaction ; the gelatine 

 which they contain is decomposed, and its 

 nitrogen converted into carbonate of ammo- 

 nia and other ammoniacal salts, which are 

 retained in a great measure by the powder 

 itself. (Bones burnt till quite white, and re- 

 cently heated to redness, absorb 7.5 times 

 their volume of pure ammoniacal gas.) 



ARTIFICIAL MANURES. 



WE have now examined the action of the 

 animal or natural manures upon plants; but 

 it is evident that if artificial manures con- 

 tain the same constituents, they will exer- 

 cise a similar action upon the plants to 

 which they are applied. We shall only 

 notice here one or two of those principally 

 employed. 



Since it has been ascertained that animal 

 manures act (as far as the formation of or- 

 ganic matter is concerned^) only by the am- 

 monia which they contain, attention has 

 been devoted by chemists to discover a 

 more economical means of presenting this 

 ammonia to plants. The water which dis- 

 tils from the retorts in the preparation of 

 coal gas is strongly charged with this alkali, 

 but is at the same time mixed with tar and 

 other empyreumatic impurities. It has been 

 customary to allow the tarry matter to sub- 

 side, and decant off the clear, supernatant 

 liquor. This liquor, being diluted to such 

 a degree as to be tasteless, is applied as a 

 manure to the field. 



Now, the ammoniacal liquor of the gas- 

 works contains the ammonia in the form of 

 carbonate and hydro-sulphate of ammonia 

 (sulphuret of ammonium). The latter com- 

 pound is a deadly poison to vegetables, nor 

 can we conceive that by dilmion its proper- 

 ties can be changed. The carbonate of 

 ammonia is volatile, and escapes into the at- 

 mosphere. To obviate this latter inconveni- 

 ence and render it more transportable, it has 

 been proposed to convert the carbonate into 

 the sulphate, by means of gypsum.* But 

 this does not remove the hydro-sulphate. 

 A more simple and efficacious method is to 

 add a solution of sulphate of iron (the green 

 vitriol of the shops) to the liquor, until no 

 further precipitation ensues. Sulphuret 

 and carbonate of iron are thus formed, and 

 the whole of the ammonia enters into com- 

 bination with the sulphuric acid, and forms 

 sulphate of ammonia. Care must be taken 

 to avoid too great an excess of sulphate of 

 iron ; and the liquor thus prepared should 

 be freely exposed to the air to promote the 

 oxidation. 



The liquor still, however, contains em- 

 pvreumatic matters, which are injurious to 

 plants. These may be removed by evapo- 

 rating the liquor to dryness, and heating the 

 residue to incipient redness. By this means 

 they are rendered insoluble, and the sul- 



* Three Lectures on Agile ultuiu, by Dr. Dau- 

 beny, page 87 



phaie of ammonia is not affected, unless the 

 heat has been carried too far. The liquor 

 properly diluted has been found very advan- 

 tageous, even without the removal of the 

 empyreumatic matter. 



Nitrate of soda has lately engaged much 

 attention, and is supposed to exert its fa- 

 vourable action upon vegetation by yielding 

 nitrogen to those of their constituents which 

 contain it. The experiments which have 

 hitherto been instituted with this manure do 

 not warrant us in concluding with" positive 

 certainty that it is the nitrogen alone to 

 which it owes its efficacy, but they certainly 

 render this a plausible explanation of its 

 virtues. Thus Mr. Pusey, the- late able 

 president of the Royal Agricultural Society, 

 has shown, that the same effects are pro- 

 duced by putrefied urine, soot, gas-liquor, 

 and nitrate of soda.* Now the three for- 

 mer act by virtue of the ammonia which 

 enters into their composition. The usual 

 effects produced by these and nitrate of soda 

 are to increase the intensity of the green, 

 colouring matter, to augment the quantity 

 of straw, but to produce a light grain. Mr. 

 Hyettf has communicated the results of an 

 analysis of two samples of wheat grown 

 under similar circumstances, one of which 

 had been treated with nitre, the other not. 

 The former contained 23-25 per cent. 01 

 gluten, and l - 375 of albumen; the latter 

 only 19 per cent, of gluten, and O62 of al- 

 bumen. Here the azotised matters appear 

 to have considerably increased in quantity. 

 There is nothing opposed to the supposition 

 that nitric acid may be decomposed by 

 plants, and its nitrogen assimilated. We 

 find that vegetables possess the power of 

 decomposing carbonic acid, and of appro- 

 priating its carbon for their own use. Now 

 this acid is infinitely more difficult to decom- 

 pose than nitric acid. But there are other 

 circumstances which oppose the adoption 

 of the view that nitrate of soda acts by vir- 

 tue of the nitrogen which enters into its 

 composition. Were this the case, the ac- 

 tion should be more uniform than it has 

 hitherto been found to be. On some soils 

 the salt does not possess the smallest influ- 

 ence ; whilst on others it affords great bene- 

 fit. We can only furnish an explanation ot 

 this seeming caprice by a reference to the 

 chemical composition or the soil upon which 

 it is applied. If the advantages attending 

 the application of nitrate of soda are due to 

 the alkaline base which it contains, then it 

 is evident that this manure can be of small 

 value on soils containing a quantity of alka- 

 lies sufficient for the purposes of the plants 

 grown upon them ; whilst, on the -other 

 hand, such as are deficient in these must ex- 

 perience benefit through its means. J In 



* Journal of the Royal Agricultural Society, 

 vol. ii., p. 123. 



t Journal of the Royal Agricultural Society, 

 vol. ii., p. 143. 



I General Sir Howard Elphinstone informs m 

 that he found carbonate of soda (soda ash) an ex 



