EMPLOYED IN AGRICULTUKE. 151 



liapliazard, but witli some degTee of discrimination, and witli 

 reference to the particular circiunstances of each case. 



Lime. — Now, amongst the whole list of bodies enumerated 

 under the general, but rather vagaie, terms of manures, or 

 fertilizers, there is, perhaps, none of more extensive use, and 

 few more important in their eftects upon the land, than 

 quicklime ; and I may, therefore, select it as the subject for 

 a few remarks, in order to illustrate the position with which 

 I set out, by showing- that, if we could enlig-hten the firmer 

 as to the manner in which it atiects the land, we mig'ht save 

 him much disappointment by explaining- when it is likely 

 to be useless, and when, perhaps, even detrimental in its 

 effects. 



I am aware, indeed, that I have selected a topic which 

 some may reg-ard as almost exhausted, for all who have con- 

 sulted the recent treatise of Professor Johnston on ag-ricultural 

 chemistry, will admit that he has communicated in it a very 

 able and correct account of the uses of lime in ag-riculture ; 

 nor, with this work before me, should I, concurring- as I do 

 in the g-eneral tenor of his remarks, have brought this sub- 

 ject before you on the present occasion, were it not for the 

 sake of drawing- attention to one in particular, among-st the 

 various uses attributable to this substance, which seems to 

 receive lig-ht from the principles that I ventured to lay dowii 

 in the conclusion of a memoir on the rotation of crops, lately 

 published in '' The Philosophical Transactions." 



In this memoir I endeavoured to elucidate the distinction 

 that exists between that portion of the ing-redients of a soil 

 which is in a state to become available for the immediate 

 purposes of the plant, owing- to its being- readily soluble in 

 the water that penetrates the ground, and that which is not 

 at present broug-ht into a condition of such easy solubility, 

 and consequently at the present moment does not contribute 

 in any deg-ree to the development of the vegetables that 

 grow in it. The former portion I have distinguished as its 

 active, and the latter as its passive ing-redients ; and I pro- 

 posed to estimate the relative amount of each, by treating* 

 the soil, first with a definite quantity of water impreg-nated 

 with carbonic acid g-as, and afterwards with diluted muriatic 

 acid, and to determine the several quantities taken up by the 

 first and by the second of these re-agents. The former I 

 conceived would be likely to represent the amount which 

 was actually apjilicable to the uses of the plant, since it is to 

 ie presumed that what could not be extracted by a larg-e quan- 



