Manures, 207 



Stable-manure, and all decomposing animal and vegetable 

 substances, have a tendency to promote the decay of stubborn 

 organic remains in the soil, on the principle that putrescent 

 substances hasten the process of putrefaction in other organic 

 bodies with which they come in contact. Salt, in a small 

 proportion, has been demonstrated, by Sir J. Pringle, to be 

 gifted with a similar septic property ; and that lime rapidly 

 breaks down the texture of organised matters is well known. 



There is no doubt that rich soils, or those abounding in 

 animal and vegetable remains, are less liable to change in 

 temperature with that of the incumbent atmosphere, than 

 those of a poorer constitution. This partly arises from causes 

 explained when treating of the influence of the colour of soils 

 upon vegetation. Some manures, as salt, protect plants from 

 suffering by sudden reductions of temperature, by entering 

 into their system, stimulating, and rendering them more vigo- 

 rous, impregnating their sap, and, consequently, rendering it 

 less liable to be congealed. (Jo/inson's Essa^y on the Uses of' 

 Salt, ed. 2. p. 129.) 



Every cultivator of the soil, by certain empirical signs, may 

 be able to determine that certain applications are required to 

 render his land productive ; for example, he knows when 

 chalk may be applied to advantage ; but no lengthened practice 

 has yet enabled any one to judge of the quality of a chalk by 

 its exterior appearance. Chemistry alone can do this. The 

 farmers of a district in Yorkshire having experienced the 

 benefit of lime, procured some from a neighbouring kiln, and 

 were astonished to behold the injury it caused to their crops, 

 and it remained an anomaly of their experience, until chemis- 

 try demonstrated that it contained a very large proportion of 

 magnesia, which, absorbing carbonic acid very slowly, remained 

 in a caustic state, to the injury of the roots of the plants, and 

 the diminution of benefit from the carbonic acid evolved by 

 the decomposing constituents of the soil. 



Every farmer in districts where marl is to be obtained, is 

 aware that it is highly beneficial when applied to the land ; 

 few of them, however, know that this various-coloured com- 

 pound of earths contains always chalk, often to the amount of 

 50 per cent. They learn, from experience, that the marl of 

 one district is most beneficial to their heavy soils ; that of a 

 second district is productive of most benefit upon light land : 

 yet they are ignorant, in the first instance, that the first marl 

 contains silica, or sand ; that the second has alumina, or clay, 

 as a component ; and, if a new pit of marl is opened, they have 

 to wait the result of some years' practice before they ascertain 

 its quality. The chemist can inform them in an hour. 

 {To be continued.) 



