416 Dr. Clarke on [Dec. 



observations from Dr. Daubeny respecting the discovery, by 

 Prof. Stromeyer, of strontianin all the varieties of that mineral ; 

 with the exception only of the coralloidal variety called " flos 

 ferri." * For this communication from Dr. Daubeny, many of 

 us are indebted ; because it was rather generally believed that 

 strontian only existed in some of the varieties of arragonite ; and 

 I shall now be thankful to any of your correspondents who will 

 point out a plain and simple process by which the presence and 

 proportion of strontian, as a constituent of arragonite, may be 

 clearly and accurately determined. The plan I have myself 

 pursued had been considered as satisfactory ; but there are some 

 objections to it which will be obvious to chemists ; it was merely 

 that of dissolving the arragonite in dilute muriatic acid, adding 

 sulphuric acid, and trying the sulphate thus formed, by nitric 

 acid ; which is supposed to have no action upon the sulphate of 

 strontian, although it dissolve the sulphate of lime. For the 

 present, therefore, I will dismiss this part of the subject altoge- 

 ther, and proceed to a few remarks upon other minerals perhaps 

 not less likely to interest your mineralogical readers. 



I believe that fine rhomboidal crystals of the magnesian car- 

 bonate of lime are rather rare. A dealer in minerals, who makes 

 occasional visits to this University and to Oxford, for the sale of 

 specimens found in the mines of Cumberland, brought lately to 

 my house what he called " cubic carbonate of lime," from 

 Alston Moor. Perceiving that the crystals were rhombic, I 

 examined the supplementary angle of a minute fragment by Dr. 

 Wollaston's reflecting goniometer, and rinding that it measured 

 73° 45', exposed this atom, which did not weigh the thirtieth 

 part of a grain, to the test for exhibiting magnesia, which the 

 same illustrious chemist, the inventor of that goniometer, has 

 himself pointed out ; namely, by dissolving it in muriatic acid in 

 a watch glass, precipitating the lime by carbonate of ammonia, 

 and then adding phosphate of soda, and drawing lines upon the 

 glass with a glass rod. The process is now well known to che- 

 mists. I mention it only because all mineralogists are not aware 

 of the extreme subtlety of Dr. Wollaston's test ; it is such that 

 a portion of magnesia, indefinitely small as to its quantity, exist- 

 ing in a fragment of magnesian limestone almost invisible to the 

 naked eye, may yet be rendered strikingly conspicuous by this 

 process ; because the binary compound which is precipitated, or, 

 as it is called, " the triple salt," consisting of the phosphoric 

 acid united with magnesia and ammonia, appears in white streaks 

 upon the glass in all parts over which the glass rod has passed. 

 This was the case in the present instance ; and as the crystals 

 to which I allude measure half an inch in their major diameters, 

 and may be had of all the Alston Moor dealers, the information 

 will, perhaps, be thought desirable. Each crystal consists of a 



» See AnnaU of Philosophy for Sept. 1831, p. 220. 



