FUNCTIONS PERFORMED BY THE SULPHATES. 113 



On grass and clover intended for hay, we may also conclude 

 that there are doubts as to the profitable use of sulphate of soda 

 applied alone, though, as in the case of turnips, there are 

 instances among those I have quoted in which it very largely 

 increased the produce. 



One remark it is necessary to make in regard to the 

 sulphate of soda applied in all the above experiments. It 

 is generally not mentioned by the experimenter whether the 

 dry or the crystallised sulphate was used. Mr Russell states his 

 to have been the crystallised, which contains, as we have seen 

 in the preceding section, above 55 per cent of water, while Mr 

 Fleming used the dry salt, which contains no water ; but none 

 of the others draw the distinction. It is obvious, however, that 

 in any future experiments with this substance, the fact of its 

 being crystallised (like common Glauber's salt) or dry, ought to 

 be carefully specified. 



5. Functions performed in the soil by the sulphates of potash 



and soda. 



The idea we form as to the functions performed by a sub- 

 stance in the soil or in the plant, will materially determine the 

 kind of experiments we shall consider likely to lead to the most 

 useful results. Before adverting, therefore, to the experiments 

 it may be desirable to institute, it is proper to state briefly 

 the principal functions, in reference to vegetation, which the 

 sulphates of potash and soda may be supposed to perform. 



In the first place, both of these salts being soluble in water, 

 are capable of supplying, in the form of sulphuric acid, that 

 sulphur which we find to exist in, and which, therefore, must be 

 a necessary of healthy life to the growing plant. 



In regard to the plants to which they are likely to be spe- 

 cially useful, therefore, we should expect them to be those 

 which require this element in the greatest quantity, or in which 

 we find it especially to abound. And as 100 parts of the sul- 

 phate of potash contain 46, and of the dry sulphate of soda 56 

 of sulphuric acid, the latter ought to be the more serviceable, 

 weight for weight, in so far as this supply of sulphur js con- 

 cerned. 



H 



