Seft. III. Agriculture and Vegetation. 53 



fore : but {till it is very different from a 

 half-vitrified fubftance ; and I much quef- 

 tion, whether or not it can, without any 

 addition, be turned into glafs. This is a 

 ftrong proof, that it contains no falts, acid, 

 alkaline, or neutral ; for thefe are capable 

 of vitrifying lime when added to it. 



Exp. 23. I could not get any fait from 

 thefe marls, either by fimple lixiviation, or 

 diftillation, though I urged them with the 

 ftrongeft fire. The fire feparated nothing 

 but a little water, which appeared to be 

 gently alkalefcent j owing perhaps to fome 

 of the finer marly particles, which were 

 carried up by the water. No oil appeared 

 in the diftillation. When the powder of 

 marl was thrown on fufed nitre, it fparkled 

 a very little. This, and the fulphureous 

 fmell arifing when it was diffolved by the 

 oil of vitriol, would incline me to think, 

 that it has a fmall proportion of an oleagi- 

 nous matter in its compofition. 



4 



3 BUT 



