1 62 LESSONS IN CHEMISTRY. 



preferred. This plan of treating them is, however, only to be 

 adopted when your object is merely to obtain the chemical 

 effects of the lime present. 



253. Abont thirty years ago, enormous quantities of the 

 powdery marl, such as that from the barony of Lecale, of 

 which the analysis is given above, were applied to the fields 

 of Down, and with such beneficial effects, it is said, as in 

 many instances to raise the value of the land fourfold. But 

 after a time the produce decreased, and marl fell into disre- 

 pute as a manure, and has not for some years been much 

 employed in that district. And so it will always happen, 

 until farmers become acquainted with the nature of the sub- 

 stances which they apply to their fields. Precisely the same 

 thing occun-ed in Nottinghamshire, with regard to bones. 

 At their first introduction, then* price being low, it was ima- 

 gined that, as in small quantity they had done good to the 

 soil, a larger supply should be even more useful ; but after 

 some time, to the great disappointment of the farmers, good 

 effects ceased to follow their application, and it was not until 

 the Duke of Portland, by the publication of the results of 

 experiments made on his farm, convinced them that the 

 soil had been overcharged with bone earth, that they directed 

 their attention to other applications. The farmers of Down, 

 in the grain exported from Strangford and Killough, had, for 

 several years, taken away from their farms nine or ten of the 

 materials which rendered them fertile, only two or three of 

 which could be replaced in the marl used to keep up the 

 condition of the soil. 



254. Shell-sand. — Valuable collections of sand, containing 

 a large amount of broken shells, exist on the coasts in many 

 parts of Ireland. As this sand usually contains both carbo- 

 nate of lime and animal matter, derived from the shells, and 

 some of the saline ingredients of the sea-water, it must pos- 

 sess considerable efficacy as manure. It may also, like marl, 

 be expected to convey to the soil a small amount of phosphate 

 of lime. It occurs of various degrees of fineness, and, as 

 might be expected, differs very much in value in different 

 localities. The fresh shell-sand from the sea-shore should 

 always be preferred to that which has been long exposed 

 at a distance from the coast, as it will contain a larger 

 amount of animal matter capable of affording ammonia by its 

 decay. 



