MANURES. 361 



farmer in Scotland, who, as far as my observation and the char 

 acter he holds in the county avail, as an intelligent and practical 

 farmer has no superior in the kingdom, he stated to me that he 

 had applied lime to his land liberally, for a quarter of a century, 

 and never saw from it any benefit whatever. On the other 

 hand, the innumerable instances in which it has been obviously 

 beneficial, and where the improvement of the land can be traced 

 to no other cause, compel one to conclude, in reference to its 

 failures, that there must be something in the soil, or in the mode 

 or circumstances of its application, not yet understood. Innu 

 merable instances are found where it has been efficacious at the 

 first application, but its repeated applications have been per 

 nicious. I have already referred to a remarkable fact, that it 

 seems most efficacious upon limestone and chalk soils. My 

 readers shall have the benefit of the opinions of one of the most 

 enlightened chemists, which I subjoin in a note.* 



* Professor Lyon Playfair, in a manuscript lecture with which he kindly favored 

 me, thus speaks : 



&quot; When a chemist in his laboratory wishes to liberate the potash or silica from 

 a soil which he is analyzing 1 , he mixes it with lime and heats them together. By 

 this means he renders soluble, in acids or in water, all that was insoluble before. 

 The farmer performs exactly the same operation as the chemist, when he limes 

 his land. He liberates, by this means, the silica, the potash, and the phosphates, 

 from the soil, and enables them to administer to the wants of vegetation. But 

 by the operation he has furnished no equivalent for that removed by the crops ; 

 and therefore it must infallibly happen, that the continuance of the system is 

 merely a continuance of a rapid system of exhausting the soil. A rich clay, 

 abounding in potash, may long survive the treatment, but is as certainly going 

 on to exhaustion as a granary of corn, out of which you take every day a certain 

 amount of grain, and merely put in its place the key with which you opened the 

 granary door. The lime is the key merely by which you opened the magazine 

 of food contained in the soil. 



&quot; I speak of it now in the principal way in which it is used ; but it not infre 

 quently happens, that it may itself supply an absent constituent of the soil, es 

 pecially in cases such as clover and grasses, which experience much benefit 

 from a top-dressing of this article. I do not say that the former use of lime is 

 illegitimate, because clays often contain potash enough to last for thousands of 

 years, if nothing more than that ingredient were required ; but, at the same time, 

 the lime aids the plants in removing sulphates, phosphates, and other ingre 

 dients, which may be required for the purposes of their organism, without restor 

 ing what is abstracted. I have frequently found, in the examination of some 

 limestones, lauded for their superior excellence, that their action seemed to be 

 due to the presence of some adventitious ingredient, such as magnesia, which 

 could have been supplied more efficiently by other means. 



&quot; There is no manure more beneficially used, or more disgracefully abused, than 



VOL. II. 31 



