1822.] of Two Finnish Minerals. ' '^^ 



tion of cobalt, it gives a red colour at the fused edges, indicatirig 

 the presence of magnesia. 



The analysis was performed as follows : A portion of the 

 mineral reduced to fine powder was ignited with three times its' 

 weight of carbonate of potash, and treated, as already described, 

 in the former analyses, with muriatic acid, and left pure silicai' 

 The muriatic solution gave a small quantity of precipitate witfr* 

 ammonia, which was separated into alumina and peroxide of 

 iron: the remaining solution gave a precipitate with oxalate 

 of ammonia ; the oxalate of lime was washed, dried, decomposed 

 by heat, and left carbonate of lime. 



The solution was then precipitated with carbonate of potash 

 at a boiling heat; the precipitate obtained was ignited and 

 weighed ; by solution in sulphuric acid, it gave a small q^ian- 

 tity of sulphate of lime, and the dissolved portion consisted 

 of pure magnesia. The mineral lost 0*32 per cent, by a red heat. 



The results of this analysis were as follow : '^ 



Sihca 54'83 containing 27.58 of oxygen « 



Lime 24-'/6 6-95 > C 



Magnesia 18-55 7-18 j 



Alumina. 0-28 -^ 



Oxide of iron 0*99 ^ 



Volatile matter 0-32 



99-73 



We find from this analysis, that the quantities of oxygen in 

 the magnesia and hme are very nearly equal, and that the oxy- 

 gen of the silica is four times that of each of the other earths. 

 This mineral is consequently composed of one atom of magnesia, 

 one atom of lime, and four atoms of silica, and its mineralogical 

 formula will be C S^^ + M S\ 



Article VIII. 



A Demonstration of a Proposition from Simson's Euclid j p. 301".' 

 By Mr. James Adams. 



(To the Editor of the Annals of Fhilosophy.) 



SIR, Stonehouse, Jan. 12, 1821. 



The insertion of the following proposition and demonstration 

 in the Annals of Fhilosophy, when convenient, will obhge 



Your humble servant, 



James Adams. 



