tOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 545 



with a knife. Its specific gravity is from 4.300 to 4.338. It effervesces with 

 acids, and melts under the hlow-pipe, though not very readily. Placed in a 

 covered crucible, in a hot parlour fire, it lost its transparency. After exposure 

 to a moderate heat in a melting furnace, it adhered to the crucible, and exhibited 

 signs of fusion ; but was not diminished in weight, did not feel caustic when ap- 

 plied to the tongue, nor had it lost its property of effervescing with acids. 

 Hence it is probable, that its loss of transparency was rather occasioned by nu- 

 merous small cracks, than by any escape of the water of crystallization, or of 

 its aerial acid. 



Exper. a. 500 grs. dissolved in muriatic acid, in such a manner that nothing 

 but elastic fluid could escape, lost in solution 104 grs. and there remained an 

 insoluble residuum of nearly 3 grs. 2. In another experiment 100 grs. lost in 

 solution 21 grs. and there remained 0.6 of a gr. of insoluble matter. 



b. 100 grs. dissolving in dilute muriatic acid, gave out 25 oz. measures of 

 air. This air was received in quicksilver, and when the spar was wholly disolved, 

 the solution was boiled in order to drive out what air might be lodged in it. 

 2. This air was heavier than atmospheric air ; it was readily absorbed by agita- 

 tion in water, it precipitated lime from lime-water, and it extinguished flame. 

 The water which had absorbed it changed the blue colour of litmus slowly * to a 

 red ; so that this elastic fluid was undoubtedly fixed air. 



c. The solution b, by the addition of mild fossil fixed alkali, afforded a pre- 

 cipitate which, after proper washing and drying, weighed 100 grs. 2. This 

 precipitate, on being again dissolved in marine acid, yielded only 20 oz. measures 

 of fixed air. 



d. To a saturated solution in marine acid mild fixed vegetable alkali was added; 

 the earth was precipitated, and a quantity of fixed air escaped. 2. The same 

 thing happened when mild fossil alkali was added. 3. When caustic vegetable 

 alkali was used, the precipitation took place, but without any appearance of 

 effervescence. 4. 50 parts dissolved in marine acid lost, during the solution, 

 nearly 10.5. This solution, on the addition of caustic vegetable alkali, let fall 

 a precipitate which, when washed and dried, weighed 45.5. 5. Phlogisticated 

 alkali precipitated the whole of the earth from part of the solution d ; for mild 

 fixed alkali afterwards added to the filtered liquor occasioned no further 

 precipitation. 



e. Part of the precipitates d, 1,2, after exposure to a strong heat in a crucible, 

 was thrown into water. Next morning the water was completely covered with 

 an ice-like crust, and had the acrid taste of lime-water in a very high degree. 



* Other acids turn the blue of litmus instantly to a red, whilst water, impregnated with fixed air, 

 does not change the litmus immediately ; but, after some seconds, the red colour begins to appear, 

 and then gradually grows more distinct. — Orig. 



VOL. XV. 4 A 



