1818.] Scientific Intelligence. 387 



carbonate of magnesia and one atom of hydrate of magnesia. — 

 (Ann. de Chim. et Phys. vii. 206.) Grotthuss has expressed a 

 suspicion that common magnesia may be a compound of carbo- 

 nate and hydrate of magnesia — (Schweigger's Jour. xx. 276) ; a 

 suspicion which seems to have been verified by Berzelius about 

 the time that it was made ; for though Berzelius's statement was 

 not published till some months after Grotthuss's conjecture, there 

 is every probability that his experiments had been completed 

 before, the publication of Grotthuss's paper. Bucholz informs us 

 that magnesia alba exists in three different states of combination. 

 These observations of Berzelius and Grotthuss may, perhaps, 

 apply correctly to the magnesia alba exposed for sale in the 

 apothecaries' shops of Sweden and Germany. In these coun- 

 tries, the chemical medicines exposed to sale are subjected to an 

 annual examination. Hence it is natural to look for more 

 uniformity in their state than in this countiy where no such 

 examination takes place, and where every chemical manufac- 

 turer is left entirely to his own judgment. I have had occasion 

 to examine a good many specimens of magnesia alba purchased 

 in druggists' shops, and I have found too great a diversity in its 

 composition to permit the conclusion that it is a chemical com- 

 pound. It seems rather to be a mechanical mixture of carbonate 

 of magnesia, caustic magnesia, and, perhaps, hydrated magnesia, 

 in different proportions. This no doubt would depend upon the 

 state of the alkali employed to throw it down from Epsom salt, 

 or muriate of magnesia ; for it is from these two salts that it is 

 usually procured. . I shall give, as an example, an analysis of a 

 magnesia alba, purchased in Glasgow, which I made last winter. 



Carbonic acid 14*0 1 atom 



Magnesia 51*4 4 atoms 



Water 28-0 5 atoms 



Sulphate of lime 6-6 



100-0 



III. Discovery of Haiiyne in the Is/and of Tt/ree. 



M. Necker, of Geneva, some time ago, discovered haiiyne in 

 the primitive limestone of the island of Tyree. The following is 

 the account of the specimens which he observed, as stated by 

 him in a letter to Professor Jameson : — 



Colour. — Sky blue, pure, and sometimes a little greenish. 

 Lustre. — Vitreous, shining. 

 Transparency. — Pellucid. 

 Fracture. — Vitreous. 

 Hardness. — Scratches glass. 



Chemical Characters.— ^With the blow-pipe does not melt, but 

 loses its colour and becomes opaque. 



2b2 



