Book III. SlPECIES OF MANURES. S55 



thirds in weight ; and tlie principal elastic matter disengaged, is carbonic acid with some 

 ammonia ; and both these, if retained by the moisture in the soil, as has been stated 

 before, are capable of becoming a useful nourishment of plants. In October, 1808, Sir 

 H. Davy filled a large retort capable of containing three pints of water, with some hot 

 fermenting manure, consisting principally of the litter and dung of cattle ; he adapted 

 a small receiver to the retort, and connected the whole with a mercurial pneumatic 

 apparatus, so as to collect the condensible and elastic fluids which might rise from the 

 dung. The receiver soon became lined with dew, and drops began in a few hours to 

 trickle down the sides of it. Elastic fluid likewise was generated ; in three days thirty- 

 five cubical inches had been formed, which, when analysed, were found to contain 

 twenty-one cubical inches of carbonic acid, the remainder was hydrocarbonate mixed 

 with some azote, probably no more than existed in the common air in the receiver. The 

 fluid matter collected in the receiver at the same time amounted to nearly half an ounce. 

 It had a saline taste, and a disagreeable smell, and contained some acetate and carbonate 

 of ammonia. Finding such products given off from fermenting litter, he introduced 

 the beak of another retort, filled with similar dung, very hot at the time, in the soil 

 amongst the roots of some grass in the border of a garden ; in less than a week a very 

 distinct eflPect was produced on the grass ; upoa the spot exposed to the influence of the 

 matter disengaged in fermentation, it grew with much more luxuriance than the grass in 

 any other part of the garden. Besides the dissipation of gaseous matter, when ferment- 

 ation is pushed to the extreme, there is another disadvantage in the loss of heat, which, 

 if excited in the soil, is useful in promoting the germination of the seed, and in assisting 

 the plant in the first stage of its growth, when it is most feeble and most liable to disease : 

 and the fermentation of manure in the soil must be particularly favorable to the wheat 

 crop, in preserving a genial temperature beneath the surface late in autumn and during 

 winter. Again, it is a general principle in chemistry, that in all cases of decomposition, 

 substances combine much more readily at the moment of their disengagement, than after 

 they have been perfectly formed. And in fermentation beneath the soil the fluid matter 

 produced is applied instantly, even whilst it is warm, to the organs of the plant, and 

 consequently is more likely to be eflicient, than in manure that has gone through the 

 process ; and of which all the principles have entered into new combinations. 



2208. Checking fermentation by covering. *' There are reasons suflficiently strong,** 

 Grisenthwaite observes, " to discourage the practice of dilowing dung heaps to ferment 

 and rot without interruption. It appears that public opinion has slowly adopted the 

 decisions of chemical reasoning, and dung-pies, as they are called, have been formed with 

 a view to save what was before lost ; a stratum of mould, sustaining the heap, being 

 placed to receive the fluid parts, and a covering of mould being applied to prevent the 

 dissipation of the serial, or gaseous products. These purposes and contrivances, unfor- 

 tunately, like many of the other operations of husbandry, were not directed by scientific 

 knowledge. To cover is so commonly believed to confine, that there is no wonder that 

 the practical cultivator adopted it in this instance from such a consideration. But it is in 

 vain ; the elasticity of the gases generated is such as no covering whatever could possibly 

 confine. If it were perfectly compact, it could only preserve as much carbonic acid as 

 is equal to the volume or bulk of air within it ; a quantity too inconsiderable to be 

 regarded, could it even be saved ; but every particle of it must be disengaged, and lost, 

 when the covering is removed." 



2209. Checking fermentation by watering is sometimes recommended ; but this prac- 

 tice is inconsistent with just chemical views. It may cool the dung for a short time ; but 

 moisture, as before stated, is a principal agent in ail processes of decomposition. Dry 

 fibrous matter will never ferment. Water is as necessary as air to the process ; and to 

 supply it to fermenting dung, is to supply an agent which will hasten its decay. In all 

 cases when dung is fermenting, there are simple tests by which the rapidity of the pro- 

 cess, and consequently the injury done, may be discovered. If a thermometer, plunged 

 into the dung, does not rise to above one hundred degrees of Fahrenheit, there is little 

 danger of much aeriform matter flying off. If the temperature is higher, the dung 

 should be immediately spread abroad. When a piece of paper, moistened in muriatic 

 acid, held over the steams arising from a dunghill, gives dense fumes, it is a certain test 

 that the decomposition is going too far, for this indicates that volatile alkali is 

 disengaged. 



2210. In favor of the applicatio7i of farm-yard dung in a recent state, a great mass of 

 facts may be found in the writings of scientific agriculturists. A. Young, in the Ussay 

 on Manures, already quoted, adduces a number of excellent authorities in support of the 

 plan. Many, who doubted, have been lately convinced ; and perhaps there is no subject 

 of investigation in which there is such a union of theoretical and practical evidence. 

 Within the last seven years Coke has entirely given up the system formerly adopted on 

 his farm, of applying fermented dung ; and his crops have been since as good as 

 they ever were, and his manure goes nearly twice as far. A great objection against 



