298 



THE GEOLOGIST. 



22. And with this knowledge, as cl basis, have been analyzed 

 and classed the innumerable varieties of silicates found in nature. We 

 dare not mention here even the approximate number of these silicates 

 considered as known. It will be almost needless, from what follows, 

 to add that long ago the study of this group of minerals became 

 incredibly difficult, their classihcation in many cases extremely doubtful, 

 and the chemical formula assigned to a great number perfectly absurd. 

 Thanks to the efforts of some very eminent men, this state of things 

 seems to be approaching its end, and a more exact knowledge of the 

 composition of silex, and of the nature of its radical silicium — 

 attained only within the last few months — seems likely to throw a 

 considerable light and quite a novel aspect on the group of silicates. 



The great physical and chemical resemblance which silicic acid bears 

 to stannic acid (oxide of tin, Sn 0') and to titanic acid (oxide of 

 titanium, Ti 0^) made us suppose, some time ago, that the former, 

 instead of containing three atoms of oxygen (Si 0^) only contained two 

 (Si 0-). This idea haunted us the more, when, reflecting upon the 

 uncertainty which has hitherto prevailed as to the atomic weight''' of 

 silicium, and still more on perusing a recent memoir by M. Gaudin, in 

 which, hj an ingenious theory of his own, the author endeavours to 

 explain the crystalline forms of bodies by a mathematical groupment of 

 their atoms. M. Gaudin told us the other day that his theory of crystals 

 had occupied, during thirty years, most of the leisure moments of his 

 active and laborious life ; and that it was impossible to explain, by its 

 aid, the crystalline form of quartz, unless he supposed this substance to 

 be Si O"'^, and not Si 0^, as was, and is, generally supposed. 



"Wohler and H. Saint Claire Deville observed lately that silicium 

 CDuld be dissolved in melted aluminium, which, on cooling, throws out 

 the former in beautiful crystals. We must remark here that a most 

 striking analogy exists between the three -elements — carbon, silicium, 

 and boron. This analogy has now become more apparent than ever, 

 and is extremely interesting in a mineralogical point of view. 



Carbon is known to exist in three distinct states — namely, 1, as 

 diamond; 2, as graphite; and 3, as a black non-crystalline powder 

 (coal, charcoal, lamp-black, &c.). Carbon combines with oxygen, and 

 forms carbonic acid (C 0^ ) and carbonic oxide (CO.) 



Silicium has just been obtained by Yfohler and Ste-CIaire Deville — 

 1, in transparent crystals as hard as the diamond, to which they bear 

 a certain resemblance ; 2, in metallic crystals, imitating graphite ; and 

 3, as a black non-crystalline powder resembling coal. Silicium combines 

 witli oxj^gen, and forms silicic acid, which we shall show presently is 

 Si 0- , and silicic oxide, discovered a few months ago by Wohler and 

 Buff, and which, in all probability, is Si O.f 



Boron has just been obtained by Deville— 1, in form of transparent 



* Tlio proportion in wliicli one body combines ^Yitll others is called in chemistry 

 its " atomic weight " or " eqiuvalent."— T. L; P. 



t This new oxide of silicium is a ^Yhitc powder ootained from chloride of 

 silicium ; when it conies in contact with water, hydrogen gas is CTolved, and 

 silicic acid formed. — T. L. P. 



