May 25, 191 ij 



NATURE 



435 



white to ruby and sapphire, at prices ranging from four 

 to ten shillings a carat, according to colour, 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 this 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 per- 

 pendicular to the plane of formation — that is to say, 

 running from the point of attachment of the pedestal to 

 the top of the mass. 



Then 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 colour is pro- 

 duced by chromium aluminate in solution or metallic 

 chromium in molecular suspension. 



A point of more practical interest is the fact that 

 although the artificial corundum is a true crystal, it 

 possesses the shape and formation 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 cannot be identified by 

 any of the physical tests I briefly referred to above. For 

 all practical purjX)ses, the artificial ruby 15 a ruby, and 

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



Fig. 3.— Section of Natural Ruby, X 100. 



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 may be present 

 in the liquid are distorted from their natural shape so as 

 to accord with this symmetrical growth. It is the great 

 ' xception to find a natural ruby entirely free from such 

 inclusions, which generally form irregular cavities with a 

 decided tendency to geometrical shape. 



In the great majority of cases examination of the cut 

 stone with a lens is sufficient to decide the artificial process 

 of formation, but in doubtful cases a more minute ex- 

 amination may be made by placing the stone in a little 

 cell filled with highly refracting liquid, in order to secure 

 regular illumination, and examining it under the micro- 

 scope by transmitted light, when the minutest trace of 

 structure can be detected. In the case of an absolutely 

 flawless stone it would be impossible to decide whether it 

 were natural or artificial, but such stones are so rare that 

 I his case is almost theoretical. 



Reconstructed emeralds have been made by the Verneuil 

 process, but these are, of course, amorphous, and do not 

 possess the double refraction and other properties con- 

 sequent upon the crystalline structure of the natural stone. 



NO. 2169, VOL. 86] 



The problem of producing this stone artificially has not as 

 yet been solved. 



The opal ranks with the diamond in resisting attempts 

 at artificial production, and is even superior to it in that it 

 cannot be really successfully imitated. 



The peculiar lustre of the pearl, like the colour of the 

 opal, is due rather to its structure than its composition. 

 It is formed in the oyster by the deposition of successive 

 layers of calcium carbonate round some central object, and 

 consists of an innumerable number of thin overlapping 

 laminae of the crystalline variety of this substance known 

 as aragonite. These layers being semi-transparent, the 

 light falling on the surface is partially reflected from the 

 surface and partially transmitted into the stone, where it 

 suffers reflection from the surface of lower layers. 



Perhaps the well-known Japanese pearl may be correctly 

 described as artificial pearl, although the oyster has a 

 great deal to do with it. 



Such pearls are formed by introducing a mother-of-pearl 

 shape between the shell and mantle of the oyster, and then 

 leaving the oyster alone for a time to allow it to convert 

 this into a pearl by the deposition of several layers of 

 nacre. The mass is then removed from the shell and 

 converted into the semblance of a true pearl by supplying 

 a back of mother-of-pearl. Such pearls, however, never 

 have the fine orient of those produced under normal con- 

 ditions, and they can readily be detected by examining the 

 back, when the lustre- 

 Jess mother-of-pearl 

 and the line of junc- 

 tion can be detected. 



Nobody has any 

 right to supply any- 

 one with paste under 

 the name of artificial 

 (or synthetic, or scien- 

 tific, if these names 

 are preferred) gem. I 

 think that the distinc- 

 tion between the two 

 should be clearly re- 

 cognised, and that it 

 should not be per- 

 mitted to use the term 

 artificial indiscrimin- 

 ately. At present this 

 is being widely prac- 

 tised ; every day one 

 sees ofTered for sale 

 " rubies, emeralds, 



sapphires, and pearls 

 artificially produced, 

 and having all the 

 properties of the natural stone." Now, as I have indi- 

 cated, such a thing as an artificial emerald answering 

 this description is unknown, and, as a matter of fact, the 

 stones supplied under this title are, as a rule, nothing 

 more or less than paste imitations, the public being 

 deliberately led to believe otherwise. There is in this 

 case, as I have indicated, a real practical difference 

 between the two articles, not merely a question of opinion. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



BiRMiSGitAM. — In the faculty of medicine an important 

 change in the organisation of clinical teaching is being 

 made. Hitherto this branch of teaching has been quite out- 

 side the control of the University. A clinical board 

 appointed by the staffs of the Queen's and General Hospitals 

 has directed the teaching and collected and administered the 

 fees of students. In future the clinical board is to consist 

 of nine members, of whom five will be appointed by the 

 University and four by the two hospitals. The board will 

 arrange all details of clinical teaching, and will nominate 

 to the council of the University persons in the hospitals to 

 act as clinical teachers, who will become members of the 

 University staff. The fees for this teaching will be paid 

 to and administered by the University. In consequence of 

 the new arrangement, medical studies will be recognised 

 by the Board of Education as a " technical " subject, in 



Fig. 4. — Section of Au .;.^.... 1,....), 



