1824.] 3T. Arfwedson's Analysis of some Minerals. 347 



precipitate be produced by boiling it after adding a little carbo- 

 nate of potash. 



0*614 gr. of this mineral, therefore, contain 



Silica (a) 0-108 



(b) 0-007 



0-115 or 18-73 

 Alumina (r) 0-500 81-43 



0-615 100-16 



18-73 silica contain 9-42 oxygen, and 81-43 alumina contain 

 38-03 oxygen; but 9-42 x 4 = 37-68. According to these 

 proportions, the formula for chrysoberyl is A 4 S. 



Boracite from Luneburg. 



Prof. Stromeyer states in a letter, of which an extract is 

 inserted in Gilbert's Annalen, xviii. 215, that he analyzed this 

 mineral, and found it a compound of 67 boracic acid and 33 

 magnesia. As Stromeyer's analyses have in general very justly 

 acquired the confidence of the public, we ought not to call their 

 accuracy in question upon slight grounds ; but as we are still 

 ignorant of the method of analysis which he employed, it is the 

 more difficult to give implicit confidence to his statement, that 

 all the methods hitherto known for separating boracic acid 

 from its combination, only accomplish their object in a very 

 imperfect manner. 



In some of my experiments to extract boracic acid from its 

 compounds, I found that if a borate (for example, borax) be mixed 

 with three or four times its weight of finely pulverized and pure 

 fluor spar, together with a sufficient portion of concentrated 

 sulphuric acid, and the matter be afterwards heated to dryness, 

 and then exposed to a red heat, we can in that way separate the 

 whole of the boracic acid in the form offluoboric acid gas. The 

 quantity of the basis being then determined, which it may be 

 with precision, we obtain the true composition of the salt sub- 

 jected to analysis.* This analytical method may be applied to 

 all borates with incombustible bases, as far as they are decom- 

 posable by sulphuric acici ; and boracite being in this predica- 

 ment, I was in hopes that I had it in my power to repeat Stro- 

 meyer's analysis with the prospect of obtaining a correct 

 result. 



* In two experiments made in this way, I have found anhydrous borax composed of 



First Exp. Sec. Exp. 



Koracicucid 686 69'2 



Soda SW JO-8 



I'M'-OO 100-00 



