168 SUGGESTIONS FOR NEW EXPERIMENTS 



experiments made on the same field in which this silicate of soda 

 was applied along with certain other substances.* 



2. To potatoes (early American) Mr Fleming applied it in 

 1842 mixed with the manure. The result was as follows : 



Manure (35 cwt.) gave . . . 8 tons l7z| cwt. 

 Manure and silicate of potash (1 cwt.) gave 15 ... 



Increase, ... 6 tons 2^ cwt. *t* 



This increase was very large ; but, supposing its correctness 

 to be undoubted, it is by no means clear that the effect was 

 due to the action of the substance as a silicate^ and not merely 

 to that of the carbonate of potash, which would be produced 

 when the silicate was mixed with the manure. 



9. Suggestions for comparative experiments with the silicates 

 of potash and soda. 



The remarks I have made in the preceding sections will have 

 shown the reader that there are many interesting questions to 

 be solved by rigorously accurate comparative experiments with 

 these silicates. I would suggest trials, therefore, in reference 

 to the following questions : 



1. Do these silicates benefit crops generally? This will 

 require experiments upon different crops with each of the sili- 

 cates ; and they may be tried in different proportions, applied 

 at different periods of the plant's growth, and either all at once 

 or in successive smaller applications. 



2. Do both of these silicates equally benefit the same crop ? 

 This suggests comparative experiments with the two silicates 

 upon the same crop and under the same circumstances, 



3. Is their effect greatest upon those plants which contain 

 much silica the grasses and corn-crops, for example or on 

 those which, like cabbage and the root-crops, contain much 

 alkaline matter ? To solve this, comparative experiments must 

 be made with each silicate upon these different classes of plants. 



* Transactions of the Highland Society, July 1847, p. 34. 

 t See Appendix to my Lectures on Agricultural Chemistry and Geology, first 

 edition, p. 63. 



