INTRODUCTION. 



affinity we may also analyze the vegetable productions, and 

 learn what ingredients each species of plant requires for its 

 most perfect growth. 



The quality of the productions themselves is also indicated 

 in these processes, for it is found that the same quantities of 

 wheat will not always make the same quantity of bread. The 

 conditions therefore on which these differences depend, we 

 may learn from an accurate knowledge, and application of 

 chemical principles. 



Another point, of great interest to the agriculturist, is the 

 theory of the action of manures, and it is to chemistry 

 that he must look for the most important histructions on this 

 subject. A knowledge of the action of saline compounds, 

 and of alkalies, is all-important to the farmer. A continued 

 course of cropping removes them from the soil, and the cheap- 

 est and most effectual means of restoring them is a matter of the 

 first necessity to a perfect system of tillage. 



And finally, " the source of the failure of crops when plant- 

 ed on the same soil for several successive years," is a subject 

 to be investigated, and its facts explained by chemical prin- 

 ciples. This will afford an explanation of rotation of crops, 

 and point out many important practical rules in regard to this 

 subject. 



In these, and numerous other ways, which we have not time 

 to specify, chemistry may afford important aid to agriculture. 

 The other chemical forces, such as heat, light and electricity, 

 not only modify the action of affinity, but act directly upon 

 the vital functions of plants. 



2. Caloric or Heat exerts an agency scarcely less impor- 

 tant than affinity itself. It also acts according to fixed 

 laws, which are known. The application of these laws to 

 agriculture, still further illustrates the utility of chemical sci- 

 ence, and is too obvious to need further specification in this 

 connection. 



3. Light is absolutely essential to vegetation, but its influ- 



