ON MANURES. 123 



certain portion of it may also be discovered, upon analysis, in 

 the natural composition of most soils. 



It has been said, by Kirwan, to accelerate putrefaction in a 

 higher degree than any other known substance; but this has 

 been shown by some experiments of Sir Humphry Davy to 

 be incorrect, and it, therefore, cannot be supposed to afford 

 any direct nourishment to plants, either by the corruption of 

 animal remains, or the decomposition of manure. It has been 

 very generally supposed that, as sulphuric acid has a great 

 attraction for water, gypsum acts by its power of attracting 

 moisture from the atmosphere ; thus cooling the air in sum- 

 mer, and being more efficacious to dry, sandy soils, than wet 

 clays. It has even been confidently stated, that the dew has 

 been known to stand two hours later in the morning upon 

 plants which had gypsum spread upon them than upon others 

 on which there was none. This, however, has been also con- 

 tradicted by Sir Humphry Davy, who considers the argument 

 in its favour to be comparatively insignificant; far, when 

 combined with water, it retains that fluid too powerfully to 

 yield it to the roots of plants, and its adhesive attraction for 

 moisture is inconsiderable : yet, though thus opposed by sci- 

 entific reasoning, the experience of farmers inclines to the 

 support of the opinion already stated. It is even thought by 

 many people that, when sprinkled over the leaves of plants in 

 a damp state, the paste which it thus forms upon them must 

 prove destructive to the propagation of many insects, and 

 would probably prevent the fly in turnips ; but that supposition 

 has not been confirmed by experience. It has been likewise 

 asserted, that its fertilizing powers are destroyed by the 

 effects of sea air, and much of its failure in many parts of - 

 England has been attempted to be accounted for upon that 

 principle ; but this is in direct opposition to the trials already 

 mentioned to have been made in Kent, and it has been found 

 to answer in Norfolk when applied to land within two miles 

 of the Northern Ocean. 



The American farmers lay it upon land newly reclaimed 

 from the forest : it may, however, be doubted whether gypsum 

 contains any inherent property by which it can improve the 

 soil, unless through the means of its fertilizing powers upon 

 the peculiar crops to which it is appropriate, and there is 

 reason to believe that, even upon these, its effects will be com- 

 paratively trifling if ploughed in. There cannot, however, be 

 any question respecting its expediency when applied as a top- 



