MINEEALOGY ; WITH A CLASSIFICATION OF SILICATES. 83 



and 1854, and then ilhistratod by the carbon-spars, pyroxenes, feklspars and tourmalines 

 — are now only, after a whole generation, beginning to be recognized by chemists. The first 

 step in this argument is believed to have been the conclusion then deduced from the study 

 of equivalent volumes, — that the law^ of condensation already knowrn in gases and vapors 

 applies also to solids ; " so that their equivalent weights, as in the case of vapors, are 

 directly as their densities, and the equivalents of mineral species are as much more eleva- 

 ted than those of the carbon series as their specific gravities are higher." By reference 

 to the context of this, as already cited in § 15, it will be seen that a notion of the import- 

 ance of geometric form in conditioning density, w^as then entertained by the writer, which 

 led him, in his paper published a few months later in 1853, on the Constitution and 

 Equivalent Volume of Mineral Species (§ 17-18) to suppose the existence of differences 

 between the volumes of isometric, rhombohedral and various prismatic species. This 

 notion was, however, soon afterwards discarded, as may be seen from the citations from 

 his paper of 1867 already given in § 12-14. 



§ 113. In further illustration of the supposed relations of density and equivalent, the 

 following additional passage is quoted from the paper last cited : " There probably exists, 

 between the true equivalent weights of non-gaseous species and their densities, a relation 

 as simple as that between the equivalent w^eights of gaseous species and their specific 

 gravities. The gas or vapor of a volatile body constitutes a species distinct from that same 

 body in its liquid or solid state, the chemical formula of the latter being some multiple of 

 the first ; and the liquid and solid species themselves often constitute two distinct species, 

 of different equivalent weights. In the case of analogous volatile compounds, as the hydro- 

 carbons and their derivatives, the equivalent weights of the liquid or solid species approxi- 

 mate to a constant qtiantity, so that the densities of those species in the case of homo- 

 logous or related alcohols, acids, ethers and glj'^cerids, are subject to no great variation. 

 These non-gaseous species are generated by the chemical union or identification of a num- 

 ber of volumes or equivalents of the gaseous species, which number varies inverselj' as 

 the density of these species. It follows from this that the equivalent weights of the liquid 

 and solid alcohols and fats must be so high as to be a common measure [multiple] of the 

 vapor-equivalents of all the bodies belonging to these series. The empirical formula 

 ^iuHi,„Oio, which is the lowest one representing the tristearic glycerid (ordinary stéarine) 

 is probably far from representing the true equivalent weight of this fat in its liquid or solid 



suborders of Silicates, arranged in part irystidlograpliically and in part cliomically. The Oxydâtes are <livided 

 between tlie Kuphoxyde and the Jletalloxyde, or those of the lighter and the heavier metals. In Halometallite are 

 found the silicates of yttrium, zirconium, thorium, cerium, zinc, copper, iron and manganese, together with 

 niobates, tantalates, tungstates, chromâtes, as well as arsenates, phosphates, sulphates, carbonates, fluorids and 

 cblorids of the heavy metals ; the corresponding compounds of the lighter metals coming under the order Apyritite 

 of Class II. In a second edition of the Synopsis, in 1884, the Halonietallite are made an order in a new class, called 

 MdalloUihe or Metalstone.s ; while the order AsjilmHilr is divided Ijy separating from it the order ^/«ofVf (Petroleums). 

 In the order of Thiomctalle, the family Pyrite includes alike the pyritoids, smaltoids, and arsenopyritoids ; Galenite, 

 the galenoids and bournonoids, and t'înnabarite, the spbaleroids and pronstoids. 



From the point of view chosen for our essentially chemical sy.steni it seems unnatural to place in two distinct 

 classes analogous and closely related oxyds, silicates, carbonates, etc. Again, the different degrees of condensation, 

 as shown in atomic volume, and in the relations of this to hardness and susceptibility to chemical change, which 

 underlie the distinction between spathoids and adamantoids, must not be lost sight of. It may be further remarked 

 that instead of making, as Mohs and Wie.sbach have done, solubility in water and sapidity the ground of a class- 

 distinction, we subordinate it to the order, constituting sui-li .solulilo species trilies of their respective orders. 



