254 Rev. Mr, Conyheare on [April, 



From the experiments which have been described, tue mineral 

 under examination may be pronounced to be an almost pure 

 carbonate of magnesia, composed in 100 grains of 



Magnesia 46*0 



Carbonic acid , 51*0 



Insoluble matter 1-5 



Water 0-5 



Loss l-O 



100-0 



The acid and base are in atomic proportion, and the stone is 

 constituted of one atom of each ; for as 46 to 51, so very nearly 

 is 24'6 to 27-5, the numbers which, on Dr. Wollaston's scale, 

 denote the equivalents of magnesia and carbonic acid. 



I avail myself of this opportunity of expressing my doubt 

 whether such a salt as the hicarhonate of magnesia j constituted 

 of one atom of base and two atoms of acid, really exists. This 

 doubt, it is true, is founded on the examination of a single speci- 

 men of a salt prepared by myself several years ago. It was 

 formed by mixing a dilute solution of sulphate of magnesia with 

 a solution of carbonate of soda highly charged with carbonic acid 

 under pressure. No immediate change occurred ; but after a few 

 days, small hemispherical masses, consisting of con^'eries of 

 crystals radiating from a common centre, had formed on the 

 inner surface of the vessel. Having a few of these left, I have 

 lately again examined them, and find them composed of base 29, 

 acid 30, and water 41 . These proportions of acid and base, 

 perhaps from some trifling impurity of the salt (on which, hav- 

 ing now exhausted my whole stock, I cannot make any more 

 experiments) do not exactly agree with the carbonate ; but they 

 are very remote from those that should constitute a bicarbonate. 

 Should any of your readers have prepared and analyzed a true 

 bicarbonate of this earth, the information will, perhaps, be 

 acceptable to others as well as to myself. 



Article III. 



On the Red Rock Mark, or Neiver Red Sandstone. 

 By the Rev. J. J. Conybeare. 



(To the Editor of the Amials of Philosophy.) 



MY DEAR SIR, Bath Eatt&n, Feb. 15, 1821. 



If the following remarks on one. of the British strata, which 

 has as yet been but imperfectly described, appear to you worthy 

 of insertion, they are much at your service. Some parts of the 



