C 19 3 



ly obvious ; a substance which had been used with 

 success in gardening, must have been soon tried in 

 in farming ; and in countries where marie was not to 

 be found, calcined limestone would be naturally sm 

 ployed as a substitute. 



The elder writers on agriculture had no correct 

 notions of the nature of lime, limestone and marie, or 

 of their effects ; and this was the necessary conse* 

 quence of the imperfection of the chemistry of the 

 age. Calcareous matter was considered by the alche- 

 mists as a peculiar earth, which in the fire became 

 combined with inflammable acid ; and Evelyn and 

 Hartlib, and still later, Lisle, in their works on hus- 

 bandry, have characterized it merely as a hot manure 

 of use in cold lands. It is to Dr. Black of Edinburgh 

 that our first distinct rudiments of knowledge on the 

 subject are owing. About the year 1755, this cele- 

 brated professor proved, by the most decisive experi- 

 ments, that limestone and all its modifications, mar- 

 bles, chalks, and marles, consist principally of a pecu- 

 liar earth united to an aerial acid : that the acid is 

 given out in burning, occasioning a loss of more than 

 40 per cent., and that the lime in consequence becomes 

 caustic. 



These important facts immediately applied with 

 equal certainty to the explanation of the uses of lime, 

 both as a cement and as a manure. As a cement, 

 lime applied in its caustic state acquires its hardness 

 and durability, by absorbing the aerial (or as it has 

 been since called carbonic) acid, which always exists 

 in small quantities in the atmosphere, it becomes as 

 it were again limestone. 



