66 



AGRICULTURAL CHEMISTRY. 



Half a century sufficed to Europeans not 

 ly to equal but to surpass the Chinese in 

 the arts and manufactures, and this was 

 owing merely to the application of correct 

 principles deduced from the study of che- 

 mistry. But how infinitely inferior is the 

 agriculture of Europe to that of China ! 

 The Chinese are the most admirable gar- 

 deners and trainers of plants, for each of 

 which they understand how to prepare and 

 apply the best-adapted manure. The agri- 

 culture of their country is the most perfect 

 in the world; and there, where the climate 

 in the most fertile districts differs little from 

 the European, very little value is attached 

 to the excrements of animals. With us, 

 thick books are written, but no experiments 

 instituted ; the quantity of manure consumed 

 by this and that plant is expressed in hun- 

 dredth parts, and yet we know not what 

 manure is ! 



If we admit that the liquid and solid ex- 

 crements of man amount on an average to 

 l Ib. daily, (f- Ib. of urine and Ib. faeces,) 

 and that both taken together contain 3 per 

 cent, of nitrogen, then in one year they will 

 amount to 547 IDS., which contain 16-41 Ibs. 

 of nitrogen, a quantity sufficient to yield the 

 nitrogen of 800 Ibs. of wheat, rye, oats, or 

 of 900 Ibs. of barley. (Boussingault.) 



This is much more than is necessary to 

 add to an acre of land in order to obtain, 

 with the assistance of the nitrogen absorbed 

 from the atmosphere, the richest possible 

 crop every year. Every town and farm 

 might thus supply itself with the manure, 

 which, besides containing the most nitrogen, 

 contains also the most phosphates; and if 

 rotation of the crops were adopted, they 

 would be most abundant. By using, at the 

 same time, bones and the lixiviated ashes 

 of wood, the excrements of animals might 

 be completely dispensed with. 



When human excrements are treated in 

 a proper manner, so as to remove the mois- 

 ture which they contain without permitting 

 the escape of ammonia, they may be put 

 into such a form as will allow them to be 

 transported even to great distances. 



This is already attempted in many towns, 

 and the preparation of night-soil for trans- 

 portation constitutes not an unimportant 

 branch of industry. But the manner in 

 which this is done is the most injudicious 

 which could be conceived. In Paris, for 

 example, the excrements are preserved in 

 the houses in open casks, from which they 

 are collected and placed in deep pits at 

 Montfaucon, but are not sold until they have 

 attained a certain degree of dryness by eva- 

 poration in the air. But whilst lying in the 

 receptacles appropriated for them in the 

 houses, the greatest part of their urea is 

 converted into carbonate of ammonia ; lac- 

 tate and phosphate of ammonia are also 

 formed, and the vegetable matters contained 

 in them putrefy ; all their sulphates are de- 

 composed, whilst their sulphur forms sul- 

 phuretted hydrogen and hydro-sulphate of 



ammonia. The mass, when dried by ex 

 posure to the air, has lost more than half of 

 the nitrogen which the excrements originally 

 contained ; for the ammonia escapes into 

 the atmosphere along with the water which 

 evaporates ; and the residue now consists 

 principally of phosphate of lime, with phos- 

 phate and lactate of ammonia, and small 

 quantities of urate of magnesia and fatty 

 matter. Nevertheless it is still a very pow- 

 erful manure, but its value as such would 

 be twice or four times as great, if the excre- 

 ments before being dried were neutralised 

 with a cheap mineral acid. 



In other manufactories of manure the 

 night-soil, whilst still soft, is mixed with the 

 ashes of wood, or with earth, both of which 

 substances contain a large quantity 01 caus- 

 tic lime, by means of which a complete ex- 

 pulsion of all its ammonia is effected, and it 

 is completely deprived of smell. But such 

 a residue applied as manure can act only by 

 the pliosphates which it still contains, for 

 all the ammoniacal salts have been decom- 

 posed and their ammonia expelled. 



The preparation of night-soil is now car- 

 ried on in London to a considerable extent. 

 Owin^ to the variable nature of the climate, 

 artificial means are employed in its desicca- 

 tion. The night-soil, after being subjected 

 to one or other of the modes of treatment 

 described below, is placed upon iron plates 

 heated by means of furnaces. 



As soon as the night-soil is coAected, it is 

 placed in large broad trenches, until a suffi- 

 cient quantity is accumulated for the pur- 

 poses of the manufacturer. But here it 

 undergoes the same process of putrefaction 

 to which allusion has been made, and ac- 

 quires a peculiarly offensive smell from the 

 evolution of sulphuretted hydrogen and 

 other gases, which are observed to escape. 

 Unless some means be employed, at this 

 stage of the process, to retain the ammonia, 

 it escapes into the atmosphere in the form 

 i of a carbonate. Various methods have been 

 proposed to effect this purpose. Some manu- 

 facturers mix the night-soil with chloride of 

 lime, and evaporate off the water by the aid 

 of heat. This possesses the advantage of 

 depriving the excrements of smell, and at 

 the same time partially fixes the ammonia 

 which would otherwise escape. Chloride 

 of lime always contains a considerable ex- 

 cess of lime ; hence part of the ammonia 

 contained in the night-soil is expelled by 

 means of it. , 



More simple and economical methods 

 might be employed. A patent, which has 

 been taken out for the preparation of this 

 useful manure, states in its specification, 

 that the night-soil is to be mixed with cal- 

 I cined mud and finely-divided charcoal. By 

 this means, the smell is completely and in- 

 stantaneously removed, and the ammonia 

 ! retained by virtue of the affinity which alu- 

 I mma and charcoal exert for that compound. 

 ! This plan is both simple and efficacious, bur 

 ,the ammonia is apt to be expelled by the 



