1818.] Scientific Intelligence. 395 



saturating both the earths ; I then evaporate the liquid to dry- 

 ness, and expose the residual mass to a heat sufficient to expel 

 the excess of acid, if any be present. The dry mass is digested 

 in water, and a little alcohol is poured into the solution to dimi- 

 nish the solubility of the sulphate of lime. By this means I 

 obtain the sulphate of magnesia in a state of solution, Avhile the 

 sulphate of lime remains behind in the state of a white powder. 

 The only source of inaccuracy in this method is the solubility of 

 sulphate of lime in water. An ounce troy of water dissolves 

 about a grain of sulphate of lime ; but more than two-thirds of 

 this is thrown down again by the alcohol ; so that three ounces 

 of water, suppose such a quantity to be employed to dissolve the 

 sulphate of magnesia, would dissolve about one gr. of dry- 

 sulphate of lime, which contains almost exactly 0-42 gr. of lime. 

 The greatest error, therefore, which can be committed in this 

 way cannot well exceed half a grain of lime. Even almost all 

 this quantity of sulphate of lime might be recovered by repeat- 

 edly crystallizing the sulphate of magnesia ; or still better, the 

 lime might be separated from the solution of sulphate of mag- 

 nesia by means of oxalic acid, 



XIV. Prehnite. 



Standish, Oct. 20, 1818. 



I take the liberty of pointing out an error into which (in your 

 Annals for Sept.) Mr. Finch has inadvertently fallen respecting 

 the discovery of Prehnite at Pouck-hill, in Staffordshire. That 

 gentleman very naturally states, that " prehnite has not been 

 found before in England ; " and he had good grounds for believ- 

 ing that to be the case ; because the discovery of it in Glouces- 

 tershire two years ago has not, I believe, ever been made public. 



In the autumn of 1816, Mr. Bakewell, who was giving lectures 

 at Gloucester, &c. discovered very finely characterized prehnite 

 in the trap-rock at Woodford, in the parish of Berkeley ; speci- 

 mens of which are in the possession of Dr. Jenner, and many 

 other collectors in this neighbourhood. 



Robert Halifax. 



XV. New Literary Institution, Cornwall. 



An institution has been established in Cornwall, denominated 

 " The Cornwall Literary and Philosophical Society," the prin- 

 cipal object of which is the cultivation of the different branches 

 of the mathematics, experimental philosophy, natural histoiy, 

 general history and biography, and the fine arts. Another object 

 »s the formation of a museum, towards which many liberal 

 donations are stated to have been already made. 



