54 ESSAYS AND OBSERVATIONS 



with the foil, fuch fubftances may be 

 more reidlly converted, in their calca- 

 rious part, into fait proper for the nu- 

 trition of vegetables, experiment alone 

 can determine. Some circumftances in 

 the manufi(5lure of nitre feem to per- 

 fuade us that they may. On the contra- 

 ry, obfervations are not wanting which 

 appear to take greatly from the probabi' 

 lity of fuch an opinion j for marles arc 

 found to produce the moft remarkable 

 efFedts on light exhaufled foils, where they 

 can find litcle or nothing proper for fur- 

 thering the nitrous procefs, or the pro- 

 dudlion of any fait we are yet acquainted 

 with. However that may be, I think 

 we are authorifed by the foregoing ex- 

 periments to affert, that marie acquires 

 nothing of a falinc nature by being ex- 

 pofed alone to the open air *. 



If no fait is formed upon marie from 



its 



• The foHowing obfervatlon, however, muft not be 

 concealeJ. Upon a Jltatum of marie, which, with 

 Others, had been ezpofed for ages to the open air, I 



found 



