228 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1911. 



phire, at prices ranging from 4 to 10 shillings a carat, according to 

 color, quality, and size. 



Whatever may be their economic importance, a very much debated 

 question, there can be no doubt as to the scientific interest of tins 

 group of artificial gems. In the first place it is a matter of some 

 interest that a mass of fused material formed in this way should not 

 only be crystalline but possess all the characteristics of a single 

 crystal. Crystallographers are agreed that each boule is a single 

 crystalline individual, with the axis roughly perpendicular to the 

 plane of formation; that is to say, running from the point of attach- 

 ment of the pedestal to the top of the mass. On the top of the boule 

 one invariably finds a mass of symmetrically arranged facets, which 

 Dr. Herbert Smith has found to correspond with the fundamental 

 rhombohedron of corundum. Judging by analogy with other mate- 

 rials, one would expect at first sight that a fused mass formed in this 

 way would be either a heterogeneous mass of minute crystals or 

 entirely amorphous, possessing the structure characteristic of glass. 

 It is well known, for example, that under similar conditions pure 

 silica yields "quartz glass," which is extensively manufactured at 

 the present time. One is tempted to dwell upon this point, and discuss 

 its bearing on such matters as the devitrification of glass, but it would 

 be entirely out of place to do so in the present paper. 



Then, again, there is the matter of coloration. One would like 

 very much to know what is the state of combination of the chromium 

 in a ruby, and whether the color is produced by chromium aluminate 

 in solution or metallic chromium in molecular suspension. In glass, 

 as is now well established, this color is produced by the optical effect 

 of ultramicroscopic spheres of metallic gold or copper, but there 

 seems to be no parallel between the two cases. 



A point of more practical interest is the fact that although the 

 artificial corundum is a true crystal it possesses the shape and forma- 

 tion of a congealed liquid or glass. The practical interest of this lies 

 in the fact that it affords the only means of distinction between this 

 artificial corundum and the naturally formed gem stone. Being of 

 exactly the same composition and crystalline structure as the natural 

 mineral, it can not be identified by any of the physical tests I briefly 

 referred to above. For all practical purposes the artificial ruby is a 

 ruby, and one can only deny that it is a "genuine ruby" if this word 

 is held to connote essentially a product found in the earth and not 

 made by man. 



And yet, owing to the curious anomaly of its structure, the artificial 

 product can almost invariably be distinguished from the natural 

 with the greatest ease. In the naturally formed stone any foreign 

 matter which may be present is coerced into following the lines 

 of growth of the crystal, and more particularly bubbles of gas which 



