I 



PHYSICAL AND LITERARY. 19 



to them, from their difFerent degrees of 

 hardriefs, and the different difpofitions 

 of the beds into which they are extended. 

 But, from what caufe proceeds the diverfity 

 in the cohelive power of marks, equal in 

 the proportions of their conftltuent parts, 

 is difficult to fay. 



It appears from the experiments rela- 

 ted in Sedl. 3. that, in different marles, the 

 jiroportion of the calcarious to the other 

 earths is not laways the fame. As this 

 diverfity may probably render a choice 

 of marles for particular foils, if not necef- 

 fary, at lead beneficial, a more minute 

 account, than that formerly given, of the 

 procefs for difcovering the proportion of 

 earths contained in any marie, may not 

 be improper. 



Having dried and powdered the marie 

 to be examined, pour, upon any given 

 weight of it, a fmall quantity of water. To 

 this mixture, well fliaken, add a little of the 

 acid' of fea- fait,* and when the confequent 



effervefcence 



* Ant mmeral acid maybe employed l«?Uh equal ad- 

 vantage, 



