40 ACTION or GYPSUM. [Appeiultz, 



Agr. Society, ii., p. 108,) has stated that a crop of clover or sainfoin contains IJ 

 to 2 cwt. of gypsum per acre, exactly the quaniiiy which the fa viiiers of Kent and 

 Hampshire find it useful to apply to their grass lands every year. This state- 

 ment aftords a vary simple explai\aiion of the use of gypsum, and one which 

 at first sight leaves nothing to be desired. But it proves too much, for it 

 supposes the whole of the gypsum which is laid upon liie grass or clover 

 field to be removed year by year in the crop, and makes no allowance either for 

 the quantity which must necessarily be carried off by the rains, or for that 

 which must be sometimes at least laid on in the forai of farm-yard or other 

 similar manure. Nor does the result i^f analysis confirm the above statement 

 as to the quantity of gypsum contained ir.. the crop of clover or sainfoin. By 

 referring to page 220, it will be seen that 1000 lbs. of dry hay do not con- 

 tain, on on average, more than 4 lbs. of sulphuric acid — equal, supposing it all 

 to be in combination with lime, to 8| lbs. of gypsum. Or a crop of 1^ tons of 

 hay contains the elements of about 30 lbs. of gypsum — only about a sixth 

 part of what is usually added as a top-dressing to the land. 



No. YIL 



SUGGESTIONS FOR EXPERIMENTS WITH THE SOLUBLE SILICATES 

 OF POTASH AND SODA. 



In the text (pp. 207 and 349,) 1 have had frequent occasions to refer to the pre- 

 sence in the soil of the silicates of potash and soda, and to their supposed action 

 in supplying silica to the stems of the grasses and of the corn- bearing plants. 

 It would be interesting in a theoretical point of view, to ascertain, by experi- 

 ment, more fully than has hitherto been done, how far the application of tliese 

 substances to the growing crops would, as a general rule, improve or otherwise 

 aifect their growth. But as those experiments which have already been made 

 (page 349), afford a strong presumption in favour of their economical value, 

 it becomes a matter of practical interest also to iijvesligate their apparent effects 

 upon each of our cultivated crops. 



These experiments are placed within the reach of the practical farmer during 

 the ensuing season, by the introduction of the above compounds into the 

 market at a reasonable rate (page 363). 1 therefore subjoin a few sugges- 

 tions for experiments with these silicates, in the hope that some of the many 

 zealous and intelligent practical men, wiio are now directing their attention to 

 the applications of chemical science to agriculture, may be induced to enter 

 upon this field of inquiry during the ensuing spring. 



1 °. In order to convey silica into the plant, it appears to be chemically indif- 

 ferent whether the silicate of potash or that of soda be placed within reach of 

 its roots. But as the silicate of soda can be manufactured very much cheaper 

 than that of potash, it is desirable above all to try the effects of this compound 

 — upon the grasses and corn-bearing plants especially. 



2°. But as in the ashes of most plants potash is found in larger quantity than 

 soda, it is possible that the effect of the silicate of potash upon some soils may 

 be so much greater than that of the salt of soda as to counterbalance the dif- 

 ference of expense. Hence the propriety of extended trials with this com- 

 pound also. 



3°. But as in the ashes of all our cultivated plants both potash atid soda are 

 found, it may be that a mixture of the two silicates may act better than either 

 alone. It will be proper, therefore, to apply such a mixture in difTerent pro- 

 portions, and to compare it effects with those of each of the silicates laid 

 on singly. 



