98 LESSONS IN CHEMISTRY. 



arrive when the most fertile soil in the country will be deprived 

 of its power of production. I have already, in chapter iii. 

 given an account of the characters of the substances which 

 plants extract from the earth for their nourishment, and also 

 directed attention to the fact that the different crops which 

 the farmer cultivates, take up these substances in urdike pro- 

 portions (55). I shall now return to this important subject, 

 and consider more fully the peculiar action which the crops 

 usually grown in the country exert on the soil. It is to be 

 regretted that so little of the information which I am about 

 to communicate, is based upon analyses of the plants of 

 our own island. This great want, I hope, before many years 

 will be supplied, and we will then be enabled with greater 

 advantage to devise plans for the economical management of 

 our farming operations. I will, in the following table, give 

 the per centage composition of the ashes of the crops most 

 important to the Irish farmer. 



141. This table will be found interesting as showing the 

 relative proportions in which the ingredients of the soil enter 

 into our crops, and it becomes of the greatest practical value, 

 when we calculate from it the amount of these substances, 

 which are every year taken away from a fann in the course of 

 cultivation. In Ireland we are destitute of that information, 

 respecting the acreable produce of the different parts of the 

 kingdom, which would be desirable in inquiries of this kind ; 

 and very few of our farmers have any accurate return of the 

 proportions of grain and straw yielded by their grain crops, 

 or of roots and leaves produced by their turnips and other 

 root crops. 



142. An examination of the annexed table, and also of the 

 tables given in chapter iii. pages 49 and 50, in which the 

 amount of dry matter and of ash contained in the crops 

 usually grown by the farmer is stated (57), will show you, 1st, 

 That the absolute quantity of the ingredients of the soil which 

 plants abstract during their growth, varies with the kind of 

 plant examined, and also with the part of the plant. Thus 

 the proportion of ash which a hundred pounds of dried wheat 

 leave when burned, is only about two pounds; while the 

 same weight of dried clover hay, and of the dried bulb of the 

 turnip, affords more than seven pounds, and the dry leaves 

 of cabbage from eighteen to twenty-six pounds. 



