402 Dr, Thomson on Anhydrous Sulphate of Soda. [Dec. 



general, it was totally wanting from the way in which the crys- 

 tals had grouped together^ or rather iU faces, in consequence 

 of that circumstance, were rendered s6 irregular that nothing 

 could be ascertained respecting the inclination of the faces of 

 the two pyramids on each other. The large angle of the pyra- 

 mid constituting the edge a was also measured ; but the measure- 

 ments deviated so much from each other that no conclusion 

 could be drawn. I rely much more upon the measurement of 

 the edge a', because all the different measurements agreed nearly 

 with each other. In some crystals, the face P was much larger 

 than the face P' making the summit of the pyramid terminate 

 not in a point but a ridge. In some crystals, a four-sided 

 oblique prism was interposed between the two pyramids ; but 

 none of these admitted of measurement. 



The crystals were firm and solid, and had a glassy appearance. 

 "When exposed to an incipient red heat, they underwent n6 

 change. When kept about two months in a damp press, they 

 had obviously imbibed moisture ; for there was an elflorescence 

 on their surface. When these crystals were heated to redness, 

 they lost about one-third of an atom of water (9'36 grains lost 

 0*3() grain), the effloresced portion became soft and loose, and 

 could easily be detached from the crystal, leaving the crystal- 

 line nucleus as perfect as ever. 



'h The specific gravity of these crystals was 2*645, determined 

 by weighing them in alcohol. In a paper printed in the Annals 

 of Philosophy iov December, 1825 (vol. x. p. 441), I give the 

 specific gravity of anhydrous ^sulphate of soda 2*640. This does 

 not deviate much from the present determination. The specifia 

 gravity now given has the greatest chance of being correct, as 

 the crystal weighed was hard and compact, and less liable to any 

 inaccuracy than the anhydrous powder, from which the former 

 determination was obtained. , 



When the crystals were exposed to a strong red heat . in a 

 platinum crucible, they underwent the igneous fusion, and on 

 cooling concreted into a foliated brittle saline mass, exactly as 

 happens to common sulphate of soda in the same circumstances. 



100 parts of water at the temperature of 67° dissolve 10*58 

 parts of this salt. When the saturated solution is set aside for 

 some time, crystals of common glauber salt shoot in it abun- 

 dantly. 



The crystals do not affect vegetable blues. Nine grains of 

 them being dissolved in water, and mixed with a solution of 

 13*25 grains of chloride of barium, abundance of sulphate of 

 barytes fell down, and the residual liquid was neither rendered 

 muddy by sulphate of soda, nor muriate of barytes. This 

 demonstrates that the acid in this salt is precisely the same, and 

 ia the same propartioa as in glauber salt. Finally, when this 



