in the CoUediofi of the Yoikshire Philosophical Society. 179 



vlty of such a mineral cannot be fixed ; because it contracts in 

 bulk when exposed to a strong degree of heat, and when dried 

 at lower degrees its weight is in proportion to the tempera- 

 ture employed; nor is it easy to ascertain the amount of ab- 

 sorption which takes place when it is weighed in water. 

 Having left it for some time in a dry atmosphere at about 60° 

 of Fahrenheit, I found that it lost in distilled water 0"57 of its 

 weight; the gain by absorption appeared to be 0*16. The 

 specific gravity calculated from these data is 1'485. 



Having in a preliminary examination of the mineral de- 

 tected nothing in it but alumine, with a little silex and a minute 

 quantity of iron, 1 proceeded to analyse it in the following 

 manner : — 



Two grains, having been ground, were treated with nitric 

 acid till they were dissolved, except a small portion which 

 remained in gelatinous flocks ; the whole was then dried, and 

 on resolution in dilute acid, silex was left behind, the weight 

 of which, after ignition, was 0*21 pai'ts of a grain. 



A drop of the solution was tested with nitrate of barytes, 

 but no trace of sulphuric acid was discovered. 



The alumine was precipitated with bicarbonate of potash, 

 and after its precipitation nothing was found in the residual 

 liquor. The precipitate was treated with a solution of pui'e 

 potash, and all dissolved but 0*005 parts of a grain, which ap- 

 peared to consist chiefly of peroxide of iron. The alkaline so- 

 lution was satui'ated with acid, and precipitated by carbonate 

 of ammonia; the precipitate, washed by decantation, was 

 dried and strongly ignited ; it weighed 0*85 parts of a grain. 



To ascertain the proportion of water, 0*62 grains of the 

 mineral in a similar state of dryness were strongly heated ; the 

 loss of weight was 0*29, or in two grains 0'935. 



The sum then of the analysis is as follows; 



Alumine 0*850 or 42*50 



Silex 0*210 10*50 



Water 0*935 46*75 



Peroxide of iron 0*005 00*25 



2*000 100*00 



I should not pretend however to determine the proportions, 

 even in so simple a combination, from the small quantity which 

 was here employed, without repeating the experiments ; and 

 I made therefore another analysis, with this variation in the 

 method pursued; that after ascertaining the quantity of water 

 by exposing eight grains of the mineral to a white heat, I ig- 

 nited liiem with ])ure potash, and brought the whole into so- 

 lution in muriatic acid. 



2 A 2 The 



