82 



KNOWLEDGE 



[Mat 1, 1891. 



bodies. Similarly it was found that by modifyiug the 

 ordinary methods of the chemical laboratory so as to 

 imitate more closely the conditions olitaiuiug in the for- 

 mation of rocks and of mineral veins, compounds could 

 be produced, ha\ing not only the chemical composition, 

 but the other characteristics of the natural minerals. 

 For instance, in the case of barium sulphate, the material 

 is produced in the laboratory by the interaction of a 

 solution of a barium salt and a solution of a sulphate. 

 It was found that if special devices were adopted so that 

 the two solutions only came in contact with extreme slow- 

 ness, the forces of crystallization came into play, and the 

 barium sulphate separated out with the form, hardness, 

 and other characteristics of the natural mineral. The 

 processes previously employed had been too rough 

 and hasty, and had not repiroduced the conditions of 

 Nature's laboratory. Water plays a part in most of the 

 ordinary chemical processes, but under the usual con- 

 ditions water cannot be raised to a temperature above 

 100^ C, since it is then converted into steam. In the 

 depths of the earth great pressures come into play, and 

 when there is at the same time a high temperature, water, 

 kept by pressure in the liquid state, acts imder very 

 special conditions. By heating silicates, such as glass, 

 with water in strong steel vessels, so that a high tempera- 

 ture and great pressure are obtained, it is found that the 

 silica is separated in the form of quartz, in crystals 

 reproducing in the most complete manner the minute 

 peculiarities, the surface markings and striations, of the 

 natural mineral. For the production of corundum, a jiiu- 

 is employed, i.e. a substance which fuses at a moderate 

 temperature and in which the alumina dissolves, to 

 separate out on cooling in the crystalline form. The 

 colour of the ruby — one of the varieties of corundum — is 

 due, not to the substance of which it is mainly composed, 

 but to a very small proportion of a colouring matter. By 

 the addition of a small amoimt of a suitable material the 

 red colour is obtained in the product of the laboratory, 

 and by varying the colouring material sapphu-e and 

 oriental emerald have been obtained. So far the size 

 of the specimens has been small, one-third of a carat 

 being about the maximum for rubies. The carat is equal 

 to four grains. A cut ruby weighing a grain would be 

 suitable for one of the smaller stones of a ruby ring. In 

 the process of cutting, however, the weight is generally 

 reduced by one half, so that the largest specimens yet 

 produced are not adapted for employment as ornaments. 

 They are, however, used in the jewelling of watches. The 

 details of the method employed at the present time in 

 their production are as follows. The chemically precipi- 

 tated amorphous alumina is heated with barium fluoride, 

 or a mixture of the fluorides of the alkahne earths, which 

 acts as a flux, and a trace of bichromate of potash is 

 added to impart the red colour. The addition of carbonate 

 of potash, which renders the fused mass alkaline, furthers 

 the formation of larger crystals. The heating is kept up 

 for several days, at the end of which time a plentiftd 

 crop of crystals is obtained. Although the aggregate 

 weight obtained in one operation amounts to some pounds, 

 the individual crystals are, as has been said, small in size. 

 It is frequently contended that the fact of reproduction is 

 the only essential point, and that the size of the crystals 

 produced is of httle importance fi-om the scientific point 

 of view. It must, nevertheless, be allowed that the 

 interest of this work will be much increased when 

 products are obtained wliich will compare in size and 

 beauty with those occiu-ring in nature. 



Of other gems, some — as the garnet and the spinelles— 

 have been prepared ; others, as the emerald, have hitherto 



pi'oved less tractable. In the case of turquois, the arti- 

 ficially prepared substance has the chemical composition 

 and the appearance of the natural stone ; but inasmuch 

 as the laboratory product behaves diflerently under certain 

 conditions, as, for instance, when heated, it must be con- 

 sidered as an approximate reproduction only, if not looked 

 upon as a mere imitation. The pearl is formed of 

 aragonite, a mineral readily reproduced by evaporating a 

 hot solution of carbonate of Ume. The peculiar beauty 

 of the pearl is, however, due to the structure resulting 

 from its mode of growth. It would be rash to hazard an 

 opinion as to whether this structure could be imparted by 

 methods at the disposal of the chemist. 



But the great problem in the artificial production of 

 gems is the preparation of the diamond, and this problem 

 is still unsolved. Popular prejudice has relegated the 

 attempt to the same category as the endeavour of the 

 alchemist to transmute the baser metals into gold. The 

 aim of the alchemist was once a legitimate object of scien- 

 tific research. In the light of modern ideas on the nature 

 of chemical elements it is so no longer. The endeavour 

 to obtain the element carbon in that transparent crystal- 

 line form in which it is found in nature, has certainly 

 nothing in common with the work of the alchemist. Yet 

 the light in which the attempt is viewed by the majority 

 is still that so graphically described by Balzac in his inge- 

 nious novel. La Beclwrche de FAbsolu. Balthazar Claes 

 devotes his life to the endeavour to reproduce the 

 diamond, and " people would scarcely speak to him — a 

 man in the nineteenth century seeking the philosopher's 

 stone. They called him an alchemist, and said he might 

 as well try to make gold. As he passed by in the street 

 people pointed hiin out with expressions of pity or con- 

 tempt." The want of success which has hitherto attended 

 the efforts of the Balthazars of real life is perhaps scarcely 

 to be wondered at. In the case of other minerals the 

 successful reproduction has generally been achieved only 

 after the minute study of the mode of natural occurrence, 

 and this has afl:brded guidance as to the best means of 

 imitating the natural process of formation. It is only of 

 recent years that the diamond has been found in its 

 original matrix, so that materials have been wanting on 

 which to base experimental methods. The chemical 

 nature of the body, a combustible substance, is so difl'e- 

 rent from that of the ruby and most other gems, which 

 are oxides or oxidized materials, that the methods to be 

 employed for its production will probably involve the 

 application of difl'erent principles. There is no reason, 

 however, to regard the problem as insoluble. When 

 sufficient guiding data have been obtained, skill will not 

 be wanting to imitate in the laboratory the conditions 

 under which Nature has worked in the formation of this 

 most beautiful product of the mineral world. 



THE HOUSE CRICKET. 



By E. A. Butler. 



FEW domestic insects have succeeded in inspiring 

 such widely difierent sentiments in the minds of 

 then- hosts as the House Cricket. To most 

 people it is far better known by the evidence of 

 the ears than of the eyes. Its shrill chirping, 

 prognosticatory, according to popular belief, of cheerful- 

 ness and plenty, reveals the performer's presence when 

 no trace of its person can be discerned ; and hke the 

 similar soimd made by its near relative, the grasshopper, 

 it is one which there is great diificulty in localising or 

 tracing to its origin. Distinct and intensely penetrating 



