FOR PROMOTING AGRICULTURE 95 



other animals, are named by chemists, carbon, oxygen and hydro- 

 gen ; in other words, charcoal, vital air and inflammable air ; and 

 these exist in the air we breathe as well as in manures consisting 

 of vegetable and animal matters. It may seem incredible that 

 the thin air, an invisible matter, should be changed in the process 

 of vegetation into solid substances, as wood and stone. But 

 nothing has been more clearly ascertained than that in 100 parts 

 of pure limestone, forty-five parts are fixed air or carbonic acid. 

 This, in the act of burning the stone into lime, is expelled ; for if 

 at that time the stone be weighed it will be found to have lost so 

 much of its original weight. It is also well known that this same 

 lime, which, slaked with water or exposed to air, falls down into 

 a powder, will immediately afterwards begin to imbibe fixed air 

 or carbonic acid from the atmosphere, and eventually, though 

 slowly, recover its original weight." 



Having remarked that while the same food furnishes nourish- 

 ment to a variety of plants, he said it is also true that plants have 

 preferences among the variety of soils, and that soils like plants 

 consist of different proportions of the same elements, and then 

 adds: 



"Four earths generally abound in soils, and these by chemists 

 are called aluminous, siliceous, calcareous and magnesian ; and of 

 these the three first are the principal, and, in familiar language, 

 well known to every farmer as clay, sand and lime. Calcareous 

 earth is considered as essential to give to soils the capacity of 

 attaining to the highest degree of fertility. Few soils, indeed, 

 are wholly destitute of calcareous matter, but very few possess 

 so large a proportion of it as would be salutary. Limestone is 

 the great source of calcereous matter. But this is of various 

 qualities. To know, then, the constitution of the lime he uses is 

 important to the farmer." 



Pursuing the chemical problem a little farther, the speaker 

 quoted Sir Humphrey Davy's explanation of manner in which 

 lime acts upon the soil, but gives preference to that of John 

 Young, a writer on agriculture, which in brief is that lime in the 

 soil acting either as a carbonate or hyper carbonate, though 

 chiefly as the latter, absorbs carbonic acid, a most important 

 article of vegetable food, which carbonic acid is copiously evolved 

 in the putrefactive process of manures ; and also, when there is a 

 scarcity of aliment in the soil, the lime absorbs carbonic acid 

 from the air and disperses it according to the calls of vegetation. 

 Having thus elucidated the theory of lime as a co-worker with 



