PReCEEDINGS OF THE KOYAL SOCIETV, 



67^ 



of -all these substances, he oiily ofctenrfs, that they agree 

 ia several retnarkable properties, distinguishing them from 

 all other bodies, that they all appear, from well authenti- 

 cated accounts, to have fallen on the earth, attended in 

 most instances by meteors or lightning, and tliat it is re- 

 markable that the native iron in all the stones contains nic 

 kel, as well as the other native irons.' 



A letter was also read on the nth March, from Mr. vnn 

 Z^ch, confirming Mr. Schroeter's observation of the change- 

 able light of the planet Ceres, which Mr. von Zach had at 

 first attributed to the haziness of our own atmosphere, un- 

 til he found that MM. Olbers and Schroeter were agreed 

 in deriving it from a real change in the light reflected. 



An Appendix to Mr. Chenevix's paper, on the Oxyge- 

 nized Muriatic Acid, was read on the 1 stli of March. 



This addition relates principally to the various muriates 

 of mercury. It appears that Mr. Berthollct once considered 

 the acid in corrosive sublimate as oxygenized, but lie after- 

 wards renounced that opinion; and Mr. Proust also thinks 

 as Mr. BerthoUet now does. Mr. Fourcroy still calls it a 

 hyperoxygenized muriate of mercury ; and of course sup- 

 poses the excess of the oxygen in corrosive sublimate above 

 that in calomel, to be combined with the acid, and not 

 with theoxid. Mr. Chenevix however determines from ex- 

 periment that corrosive sublimate contains no particle of hy- 

 peroxygenized muriatic acid. In ico parts, he finds 60, 

 of mercury, 12.3 of oxygen, and 18 of muriatic acid ; but 

 in calomel, 79, 9.S and 11.5 respectively ; so that in calo- 

 mel the metal is less oxidized, and the oxid is combined 

 with a smaller proportion of the acid.- A piece of copper 

 was found to throw down from a solution of corrosive subli- 

 mate a very pure calomel. Mr. Chenevix observes that 

 Schecle's calomel contains a portion of subnitrate of mercury 

 precipitated witli it by the water; and that this may be 

 avoided either by using the nitrate of mercury before it has 

 boiled, or by adding to the dilute solution of muriate of 

 soda, by which it is precipitated, a little muriatic acid, to 

 engage the superfluous subnitrate. By passing a current of 

 oxygenized muriatic acid gas through water containing red 

 Olid of mercury, a true hyperoxygenized muriate was ob- 

 tained, more soluble than corrosive sublimate, and distin- 

 guishable by its smell when decomposed ; and the remain- 

 ing oxid became of a dark brown colour. 



The meetings of the 2sth of March, and the island 8th 

 of April, were occupied by part of a paper on the corundum, 

 by the Count dc Bournon, F.R.S. 



The Count de Bournon had already stated some mineralo- 

 gical reasons for classing the corundum with the sapphire 

 and o'her oriental gems : their affinity was afterwards con- 



firmed by the analysis of Mri Klaproth ; yet Mr. Haiiy siUl 

 hesitating to admit that they ought to be placed near to eacH 

 other in the system, the Count de Bournon endeavours to 

 establish the character much more fully. He divides the 

 specimens of corundum into two principal kinds; the one 

 larger, less regularly formed, and generally of a greyish co- 

 lour, capable of being easily reduced by fracture to a rhom- 

 boidal form : the other kind more regularly crystallized, 

 and of more diversified colour. 



'J"he author proceeds to consider the different varieties of 

 the corundum, first with regard to colour, which chiefly 

 constitutes the distinctions of the sapphire, the oriental ru- 

 ty, topaz, emerald, and chrysolite ; and afterwards with 

 respect to transparency, hardness, and other particulars. 

 He observes that these stones strike fire with steel less readily 

 than flint : that they are phosphorescent when rubbed in the 

 dark, the ruby in particular emitting a light similar to 

 that of red hot iron. The specific gravity varies, that of the 

 sapphire being usually about ■!.! , but most of the other va-' 

 rieties generally 3.g. The diversified forms of the crystals 

 are next considered, the basis of them all being a rhomboid, 

 contained by parallelograms, of which the angles are 96°, 

 and 84": the specimens of , an original rhomboid of this 

 kind are very rare. The derivative crystals have their an- 

 gles variously replaced, the portions thus becoming more 

 or less regularly formed pyramids. 



The cohesion of these gems is next compared with their' 

 colour, and a genera! connexion between these qualities 

 is found: the blue being in general the most difficultly 

 broken. Several circumstances respecting the crystalliza- 

 tions are still more minutely described, and the figures to 

 .which the reflection of light is owing are particularly con- 

 sidered. The author observes that in order to form the ap- 

 pearance of the rays of a regular star, by reflection from the 

 laminae of these gems, which has frequently given them the 

 denomination of asterites, the best section is to make them 

 terminate obtusely a little below the sharp angle of the' 

 rhomboid. The objections of Mr. Ilaiiyto classing the 

 sapphire and other oritntal gems with the corundum are still 

 further considered. An analogy to the two principal divi- 

 sions of corundums into regular and irregular crystals, is 

 shown in the forms of the feltspar, which is similarly dis- 

 tinguished into the very different appearances of felispar in 

 granite, and the crystallized adulaiia, besides some other 

 similar variations. The matrix of the corundums,. particu- 

 larly in the Carnatic, is a rock of a loose texture, some- 

 what resembling sandstone in appearance, but containing 

 small masses of a substance irregularly crystallized, which 

 is decomposed by exposure to the air, and then appears to. 



