298 
THE GEOLOGIST. 
22. And with this knowledge, as a 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 difiicult, their classilieation in many cases extremely doubtful, 
and the chemical formula assigned to a great number perfectly absurd. 
Thanks to the elforts of some very eminent men, this state of things 
seems to be approaching its end, and a more exact knowledge of the 
composition of silcx, 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, hy 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 0'^, and not Si 0^ as was, and is, generally supposed. 
Woliler 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 bet\\'een the three elements — carbon, silicium, 
and boron. This analogy has now become more apparent than ever, 
and is extremely interesting in a minoralogical 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 (C 0.) 
Silicium has just been obtained by Wihler and Ste-CIaire Deville — 
1, in transparent crystals as hard as the diamond, to which thoy bear 
a certain resemblance ; 2, in metallic crystals, imitating graphite ; and 
3, as a black non-crystalline powder resembling coal. Silicium combines 
with oxygen, and forms silicic acid, which we shall show presently is 
Si 0^ , and silicic oxide, discovered a few months ago by Wohlcr and 
Buff, and which, in all probability, is Si O.f 
Boron has just been obtained by Deville — 1, in form of transparent 
« The proportion in wliich one body combines vitli others is called in chemistry 
its " atomic weight " or " equivalent." — T. L. P. 
t This new oxide of silicium is a white powder obtained from chloride of 
silicium ; when it comes in contact with water, hydrogen gas is evolved, and 
silicic acid formed. — T. L. P. 
