128 COMPARATIVE EXPERIMENTS SUGGESTED. 



Has it really one action when applied to the root in the soil, 

 and another different chemical action when applied to the leaf 

 in the air ? If so, these experiments will exhibit it. 



d Compared with diluted sulphuric acid, and with the sul- 

 phates of soda, potash, magnesia, and baryta, or with one or 

 more of them, in the proportions expressed by the numbers in 

 section 8, Chapter V. namely, 



Strong sulphuric acid, 



Sulphate of potash, 



Sulphate of soda, (dry, or anhydrous,) 



Gypsum unburned, 



burned, 



Sulphate of magnesia, 

 Sulphate of baryta, 



crystallised, 



G2 Ib. 

 109 ... 



89 ... 

 202 ... 

 108 ... 



86 ... 

 155 ... 

 146 .. 



The mode of making these comparative experiments has 

 already been described, and the object or purpose of them is 

 sufficiently obvious. 



e Is its action really special upon all leguminous crops, or is 

 its peculiar action confined to a few of these ? Does it show no 

 marked influence upon the growth of any of the grasses or 

 corn-bearing plants, or on any of our root-crops ? Or does it 

 exhibit such an effect only on some soils or in some climates ? 



These inquiries alone involve a large extent of experimental 

 research. Given by experiment that in a certain soil it peculiarly 

 favours the growth of clover, will it equally favour also that of 

 tares, peas, beans, and of leguminous shrubs and trees? Again, 

 will it in the same soil produce a less sensible effect on wheat, 

 oats, barley, rye, Indian corn, &c. ? And again, what effect in 

 the same soil will it have upon turnips, carrots, parsnips, beet, 

 mangel- wurtzel, cabbage, radishes, &c., either put in along 

 with the manure, or with the seed, or strewed on the leaves 

 when they are more or less fully expanded ? 



How many carefully conducted experiments will it require to 

 determine all these points, and especially if we consider how 

 very much they may be extended and varied? 



f The effect of gypsum in soils which are rich and in others 

 which are poor in lime. To ascertain this precisely, in regard 



