WITH SULPHATE OF MAGNESIA. 137 



its beneficial action at all proportioned to the quantity of mag- 

 nesia contained in a crop ? Has it any special action upon crops, 

 such as mangel-wurtzel, in which there is comparatively little 

 magnesia ? What is its effect on the quantity, quality, and 

 general appearance of different crops ? 



c Its special action, compared with that of gypsum, with the 

 view of ascertaining if the one is more favourable to those 

 which contain much lime, the other to those which contain 

 less. 



d Its action, compared with those of chloride of magnesium 

 magnesia dissolved in muriatic acid nitrate of magnesia, carbo- 

 nate of magnesia, and sulphuric acid. This series of expe- 

 riments would have for its object to ascertain whether this 

 salt exercises any special action as sulphate of magnesia, unlike 

 or different from that exercised by its acid, or its magnesia, 

 when presented to the plant in any other form. I attach much 

 weight to the determination of this point, though it is not easy 

 to chalk out such a line of experiment as shall clearly and 

 indisputably lead to satisfactory conclusions. 



e Comparative trials with different quantities of the salt, 

 from 1 to 4 cwt. per acre, applied at different periods in the 

 autumn and spring all at once, or in successive portions at 

 successive periods with the seed, or as top-dressing in spring 

 and in the case of root crops with the manure or after the crop 

 is above the ground. 



/ In making such experiments with sulphate of magnesia, 

 regard must be had, as in the case of gypsum, to the quantity 

 of magnesia which may be naturally present in the soil. This, 

 as I have already shown, (p. 19,) will depend very much upon 

 the geological formation of the district in which the experi- 

 ments are undertaken. 



7. Suggestions for experiments with sulphate of iron. 



Sprengel had stated that sulphate of iron, when applied as a 

 top-dressing to grass land in small doses, was productive of 

 good effects. Recent experiments in France have confirmed 

 this statement. It is said to impart greater vigour and a more 

 healthy appearance to the crop, though exact numerical results 



