FOREIGN OOKKESPONDENCE. 



299 



crystals resembling the diamond, thougli generally of a reddish tint, 

 and in this state it is the hardest of all substances yet known,"^' and 

 scratches the diamond with ease ; 2, in metallic crystals, resembling 

 graphite ; and 3, as a black amorphous powder. Boron combining with 

 oxygen forms boric acid (a white crystalline powder much resembling 

 silicic acid by its chemical properties), discovered in 1872 by Homberg, 

 found in 1 776 by HoefFer and Mascagni in the waters of the Lakes of 

 Castel IsTuovo, Monte- Cerboli, &c., in Tuscany, and hitherto regarded as 

 JBo 0^ ; that is, formed with one atom of boron combined with three atoms 

 of oxygen. But as boron is isomorphousf with tin, and as stannic 

 acid, silicic acid, carbonic acid, and titanic acid contain onl}'' two atoms of 

 oxygon, it is probable that boric acid will sooner or later turn out to be 

 1)0 0^ . ISTo other oxide of boron has yet been discovered. 



Many chemists have endeavoured to ascertain the atomic weight of 

 silicium, which is generally thought to be 22. M. Marignac, the well- 

 known and indefatigable chemist of Geneva, has just found that this 

 number must be changed to 14; and that silicic acid is, consequently, 

 composed of one atom of silicium and two of oxygen (Si 0" ). When M. 

 Dumas presented this result to the Academy of Science at Paris, a few 

 days ago, it created, as may well be imagined, considerable sensation. 



The illustrious Berzelius himself had once remarked the probability of 

 this formula, and Leopold Gmelin always looked upon quartz as composed 

 of one of silicium and two of oxygen. Mr. Miller in his " Mineralogy " 

 advocates the same opinion, which was even suspected to be the exact 

 one thirty years ago by Dumas ; and, finally, M. Gaudin, M. Marignac, 

 and ourselves only waited for sufficient experimental proof to adopt it 

 once for all. Indeed, we v/ere on the point of again consulting our 

 balance to investigate this question anew, when the results obtained by 

 M. Marignac were laid before us.t 



M. Hermann von Meyer, the well-known palosontologist, whosename 

 has already appeared in one of oar former papers, has announced to the 

 Academy of Sciences of Paris, that he is about to send to that Society 

 a work which he describes in these words : " My work treats of the 

 Archegosaurus, the most marvellous animal that ever existed. The 

 creature belongs to the family of the Labyrinthodonts, which became 

 extinct before the end of the Triassic epoch. I have been fortunate 

 enough to determine the entire organization of the Archegosaurus§ at 

 each period of its life. It was in studying this animal that I first 

 discovered the persistence of the embryonic condition of the vertebral 



* Until now the disimond has been considered the hardest substance in nature, 

 — T. L. P. 



f " Taking the same crystalline form." — T. L. P. 



X Marignac's Paper, which is extremely interesting, has been published in the 

 Comptes Rendus of the Paris Academy of Sciences for the 3rd of May, 1858. Its 

 purely chemical nature prevents our laying the details of it before our readers.— 

 T. L. P. 



§ For some late observations on the Archegosaurus by Professor Owen, and an 

 examination of some of M. von Meyer's views of its structure, see Annals Nat. 

 Hist., 3rd Ser., vol. I., p. 320. — Ed. Geol. 



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