36 THOMAS STERKY HUNT ON A NATURAL SYSTEM IN 



an indefinite divisibility of molecules, adopted by Laurent, and the complex formulas, 

 necessarily including* many atoms of base, employed by tbe writer, further supplemented 

 by the conception of crystalline admixtures of homceomorphous species. 



§ 28. It was not until 1860 that the doctrines of high equivalents and the existence 

 of polycarbonates and polysilicates, maintained by the writer in 1852 and 185-3, found an 

 advocate; when Ad. Wurtz again put forth thenotionof polysilicates, explaining their gene- 

 sis from the union of several molecules of silicic hydrate and the successive elimination of 

 water. He cited in this connection the example of the metastannates of Frémy, which 

 contain five quadrivalent molecules of tin. Wurtz did iiot, however, attemjit in any way 

 to discuss the difficulties presented by the composition of the native polysilicates (for 

 certain of which he proposed structural formulas), or to fix their equivalents, and he seems 

 to have overlooked the earlier contributions to the sulyect by the present writer.' 



§ 29. In 1859, in a paper on " Euphotide and Saussurite,"- the writer having made 

 an extended chemical and mineralogical study of the tj^pical saussurite, as found in the 

 euphotide of Monte Eosa, in Switzerland, showed that it was not a feldspar, as generally 

 supposed, but a finel}^ granular or compact silicate, having the hardness of quartz, a 

 specific gravity of 3.365-3.385, and the composition of a lime-soda epidote or a zoisite, to 

 which latter species it was referred. In this connection he called attention to the obser- 

 vation of Eammelsberg, that zoisite is a]>parently identical in centesimal composition 

 with meionite, the most basic of the scapolites, which has a hardness of 6.0, a specific 

 gravity of 2. 6-2. '7, and is readily decomposed by strong acids. It was further noticed 

 that while boiling concentrated siilphuric acid did not attack pulverised saussurite " it 

 was, however, partially decomposed by this acid after having been strongly ignited." 

 Attention was then called to changes produced in the denser silicates by heat, and it was 

 noted that epidote, according to Eammelsberg, has its density reduced from 3.40 to 3.20 

 by ignition, while saussui'ite, according to the original observation of Saussure himself, 

 is converted by fusion into a soft glass having a density of 2.8. The specific gravity of 

 garnet was found bj" Magnus to be reduced one fifth by fusion, and that of idocrase from 

 3.34 to 2.94." The silicates thus modified by heat are, like meionite and uephelite, decom- 

 posable by acids, and all these facts were adduced as evidences that the action of heat is to 

 reduce such complex silicates to simpler and less dense forms. 



§ 30. In conclusion it was said that " the two silicates zoisite and meionite offer a 

 remarkable example of that isomerism in mineral species upon whose importance I haA^e 



■ Ad. Wurtz, Eep. de Chimie, 1860, ii. 464 ; also Jour. Chem. Soc, of London, 1862, p. 387 ; and Leçons de Philo- 

 sophie Chimique, 18G4, p. 180. See farther, on polypilicates, Naquet, Principes de Chimie, 1867, i. 175. 



- Contributions to the History of Eujiliotide and Saussurite, Amer. Jour. Science, 1859, sxvii. 336-349. 



'■' The observations of Greville AVilliams on beryl show that this mineral, having a density of 2.fi5-2-69, when 

 fused before the oxyhydrogen blowpipe gives a clear glass, which may be scratched by quartz, and has a density of 

 2.40-2.42. The fu.sion of quartz gives in like manner a glass to which adensity of 2.22hasbeen assigned. Williams, 

 in repeating the experiment with rock-crystal of density 2.65, obtained before the oxyhydrogen blowpipe fused 

 globules which in five experiments gave a specific gravity of 2.17-2.21. He noted moreover that alumina thus 

 fused, as in the ex25eriments of Gaudin, becomes crystalline on cooling, and has a density of only 3.45 ; that of 

 corundum being about 4.00. The crystals of alumina got by the niothod of Frémy and Fell, which consists in 

 decomposing an aluminate of lead liy fusion in contact with silica, have however all the characteristics of corundum, 

 and a density of 3.9-4.1, (Greville Williams, Proc. Roy. Soc. London, 1873, p. 409, and also Fouqué and Michel 

 Levy, Synthèse des Minéraux, etc., p. 222.) 



