

121 



c Mr M'Lintock, Lanarkshire. 



Nothing ..... produced 136 cwt. 

 Sulphate of soda, 2 cwt., . . ... 200 ... 



Gypsum, 8 cwt., . . . ... 189...* 



The numerical results above given are far from being satis- 

 factory ; and it is obvious that, if any scientific results are to be 

 extracted out of field experiments with this substance, all the 

 necessary experiments are yet to make. Practice is so far 

 satisfied, that in certain districts no doubt exists as to its being 

 a most profitable application ; but it is not so everywhere, or 

 in regard to all soils, or to all crops. Both practice and science, 

 therefore, require further explanations as to what crops it espe- 

 cially favours how, why, where, when, and to what precise 

 extent. To give a sure basis for such explanations, we must 

 possess the results of varied experiments skilfully devised, 

 conscientiously conducted, and rigorously tested by weight and 

 by measure. 



2. Theory of the action of gypsum. Why it does not produce 

 equal effects everywhere and on all crops. 



These two questions have given rise to much discussion, and 

 to many differences of opinion. The simplest answers to both 

 questions were those given by Sir Humphry Davy, that those 

 crops which naturally contained, and therefore were presumed 

 to require for their natural growth, the largest proportion of 

 gypsum or of sulphur, were most likely to be benefited by an 

 application of this substance, and that those soils in which a 

 sufficient supply of gypsum already existed, would be least 

 grateful for it when spread upon them. This explanation 

 appeared to be confirmed by the analyses which he and other 

 chemists subsequently made. These showed that gypsum does 

 actually exist in our clover crops, and that soils, upon which the 

 use of it produced no profitable effects, actually contained 

 gypsum already. But various facts, observed from time to 

 time, have been considered to throw doubt on the opinion of 



* Transactions of Highland Society, January 1849, p. 439. 



