PHYSICAL AND LITERARY 51 



It may be objecfled, that the heat em- 

 ployed in the foregoing experimencs was 

 too incon-fiderable to promote the folu- 

 tion of the f dt contained in the marles 

 under examination. But, to obviate this 

 objedion, it muft be confidered, that the 

 hear, in which thefe experiments were 

 made, greatly exceeded any heat to which 

 the foil in our climate is ever expofed. 

 From whence it is evident, that whatever 

 proportion of fait our marles may ac- 

 quire from the air, this fait never can 

 contribute by its folubility to vegeta- 

 tion ; and confequently marles cannot 

 adl in the manner that is generally fup- 

 pofed. Befides, to remove all doubt with 

 regard to this point, I boiled in water, 

 during an hour, two drachms of the 

 marie of Experiment 30. This marie, 

 when afterwards feparated by filtration 



and 



drachms of water, I found, that one drop cf this mixture 

 could, by the alkaline folution, be dilcovered in two oun- 

 ces of foft water. But no more than a fixth part of that 

 drop, at the utmoft, can be confidered as fait; there- 

 fore, one drop, equal in weight to a grain of pure fait, 

 wild be difcoverable in twelve ounces of water. 



