May 1, 1891.] 



KNOWLEDGE 



81 



^^ AN ILLUSTRATED "^i^ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: MAY 1, 1891. 



CONTENTS. 



The Artificial Reproduction of Rubies and other 



Precious Stones. By Vauguan Cornish. B.Bc, F.C.S. 81 



The House Cricket. By E. A. Butler 82 



Clustering Stars and Star Streams. By J. E. Gore, 



F.R.A.S 85 



What is a Volcano ? By the Rev. IT. N. Hutchinson, 



B.A., F.G.8 87 



Notices of Books 89 



The Pleiades Cluster, and its Probable Connection 



with the Milky Way. By A. C. Ranvard 91 



Letters :— E. E. Barnard ; Rout. W. D. Christie ; W. H. S. 



MONCK 93 



The Face of the Sky for May. By Herbert Sadler, 



F.R.A.S 96 



Whist Column. By W. Montagu Oattie, B.A.Oson. ... 97 

 Chess Column. By C. D. Locock, B.A.Oxon. 99 



THE ARTIFICIAL REPRODUCTION OF RUBIES 

 AND OTHER PRECIOUS STONES. 



By Vaughan Coenish, B.Sc, F.C.S. 



IN speaking of the artificial reproduction of precious 

 stones, it must be understood that we are dealing 

 with processes wliicli have nothing in common with 

 the iwitiition of gems. Ingenuity and skill, and 

 even a certain amount of scientific knowledge, have 

 been exercised in imitating diamonds, pearls, and so 

 forth ; but the art is merely one of counterfeit, the mate- 

 rials produced at most deceive the eye, and they possess 

 neither the chemical composition nor the properties of 

 the natural objects which they simulate, except the 

 qualities of colour and lustre. In these two points the 

 counterfeit is often sufficiently good to deceive any save 

 a practised eye ; but it must be borne in mind that the 

 intrinsic value of a gem, apart from the fictitious value 

 due to i-arity, depends not solely on beauty of colour and 

 histre, but on the hardness of the material which pre- 

 serves, for instance, a cut ruby from deterioration for 

 centuries. It is the character of permanence which gives 

 to precious stones their pre-eminent, value among other 

 beautiful objects. 



Ikit the ruby may not only be imitated more or less suc- 

 cessfully by colouring a dense and highly refracting kind 

 of glass ; it can also be irjinnlKcol, that is to say, the thing 

 itself can be prepared in the laboratory. Such a product 



is termed an artiiinnl ruby, and the common acceptation 

 of the word appears to carry with it a prejudice, as if it 

 were intended to convey that the object would be a ruby 

 were it not tliat rubies are formed naturally, whereas this 

 was produced through the intervention and contrivance of 

 man. So much is this the case that if, as may well 

 happen, rubies should prove to be produceable of sufficient 

 size for the purposes of the jeweller, there will certainly 

 be a feeling against wearing the stones so produced as 

 ornaments, due to the idea that the jewel is in some sort 

 a sham. This is a natural but mistaken conception. A 

 mineral — the rnby, for instance — is a body having a 

 certain chemical composition and other equally important 

 characteristics, such as those of its crystalline form, 

 specific gravity and hardness. The body is formed through 

 the operation of certain laws of chemical combination 

 and of crystallization. Whether the opportunity for the 

 operation of these laws occurs in the bowels of the earth 

 or in the crucible of the chemist, cannot be rightly held 

 to afi'ect the identity of the body produced. 



The reproduction of minerals has been carried on for 

 the last forty years, chiefly among a small school of 

 French chemists, and is to be regarded as a part of the 

 great work of chemical STOtbesis. 



Synthetical or constructive work only begins at an 

 advanced stage in the study of an experimental science, 

 and the synthesis of minerals was necessarily preceded by 

 many years of analytical investigation. In the first 

 decade of the present century, the laws which regulate 

 the proportions in which the elements enter into chemical 

 combination were already established. At this time the 

 art of chemical analysis was being rapidly developed, and 

 its methods were applied to the examination of minerals. 

 It was found that the elements they contained were 

 present in those particular, definite proportions which 

 bad been found to be characteristic of chemical combina- 

 tion. It was during this epoch also that the laws of 

 crystallography were first established. The chemical 

 composition and the crystalline form were recognised as 

 the two most essential characteristics of each mineral 

 species, although other properties were duly taken account 

 of, as, for instance, specific gra\-ity, hardness and colour. 

 Thus mineralogy was put on a sound footing as a classifi- 

 catory and analytical science ; but the next step in 

 advance, the introduction of synthesis, the building up of 

 the minerals, appeared to be beyond the power of the 

 experimentalist. It was found that substances prepared 

 in the laboratory, having the same chemical composition 

 as natural minerals, did not possess their other charac- 

 teristic features. Thus Heavy Spar has the same chemical 

 composition as the sulphate of barium produced in the 

 laboratory ; but whereas the first is a hard, well-erystal- 

 lizcd body, the second is formed as a fine powder, destitute 

 of coherence and of crystalline form. 



Again, silica occurs in nature as the well-known Kock 

 Crystal, but in the ordinary chemical process it is obtained 

 as a gritty powder. The silicates, a class of substances 

 comprising many well-crystalli/.od gems, such as the 

 garnet, could only be reproduced artificially as ylasses, 

 transparent indeed and coherent, but without crystalline 

 structure. Such failures gave rise to the impression that 

 there was some special intluonco or force at work in nature 

 in the production of minerals which could not be com- 

 manded by the chemist, just as it was supposed that the 

 substances produced in the vegetable and animal kingdoms 

 needed the action of the so-called riud /'on,-, and were 

 incapable of reproduction in the laboratory. The belief 

 in this ii'(<(/ tone was dispelled when the advance of 

 chemistry solved the problem of the synthesis of organic 



