1819.] Dr. Clarke's Observations on Geklenite. 453 



account of the alkali, and by no means adding to the amount of 

 the constituents by any conjectural addition. 



There remains now only two more substances to be added to 

 the list ; namely, magnesia and potass. 



F. The first, i. e. the magnesia, was separated from the lime by 

 a process recommended by Dr. Henri/, of Manchester ;* namely, 

 by adding to the residue collected in D more than its own weight 

 of strong sulphuric acid ; afterwards applying a sand heat until 

 the acid ceased to rise ; and then raising the heat so as to expel 

 the excess of the acid. The dry mass was then digested in 

 twice its weight of cold distilled water, to which I added a few 

 drops of alcohol. This dissolved the sulphate of magnesia, and 

 left the sulphate of lime, which was collected on a filter. The 

 magnesia was then precipitated from the sulphate by the carbon- 

 ate of potass in a heat approaching to 212° of Fahr. ; but the 

 whole of the precipitate of the carbonate of magnesia, after being 

 washed and dried, weighed only a single grain, allowing for base 

 only 025. 



From all the preceding experiments, the constituents of 

 gehlenite may be thus given : 



Grains. 



Water of absorption 6*00 



Silica, see A 29*50 



Oxide of iron, see C 12*20 



Lime, deducting magnesia, D 27-55 



Alumina, E 14*50 



Magnesia, F 0*25 



Potass, and loss 10*00 



ioo*oo" 



I remain, &c. &c. 



Edward Daniel Clarke. 



Article VIII. 



Observations on a Memoir by the Abbe Hauy on the Measure- 

 ments of the Angles of Crystals, and on another bu M. Cordier 

 on the Blue Carbonate of Copper. By H. J. Brooke, Esq. 

 F.R.S. &c. 



I.ontUn, Nov. 8, 1819. 



In the Annals of Philosophy for June last, a translation is 

 inserted of a memoir by the Abb6 Hauy, on the measurements 

 of the angles of crystals, in reply to some observations by Mr. 

 VV. Phillips, published in the Geolog. Trans, on the importance 



* Elements of Chemistry, vol. ii. p. 488. Lond, 1815* 



