i8o 



NATURE 



[December 22, 1904 



I 



As an example of the successful accomplishment 

 of a difficult task, we reproduce (Fig. i) the photo- 

 graph of kittiwake gulls nesting on the precipitous 

 face of a cliff, approach to which was effected by climb- 

 ing down a narrow guUey and then scrambling over 

 seaweed-clad boulders, to the imminent peril of the 

 camera. 



As a specimen of really excellent bird-photography, 

 we present to our readers the picture of a group of 

 young ringed plovers (Fig. 2), the mottled down of 

 which harmonises so admirably at a short distance with 

 their surroundings. 



If it be said that this notice is purely commendatory, 

 and contains nothing in the way of criticism, the reply 

 is that we have found nothing to criticise or to con- 

 demn. It is real nature-study. R. L. 



Jl 



THE ARTIFICIAL PRODUCTION OF 



RUBIES BY FUSION.' 

 HIS memoir opens with a short historical account 

 of the attempts previously made to produce 

 rubies by fusion, starting with the researches under- 

 taken by Gaudin with the view of obtaining fused 

 alumina in a transparent state. He obtained by 

 fusing potassium or ammonium alum, together with 

 a little chrome alum, small globules, which became 

 opaque on solidification, but had the composition of 

 the ruby. These were shown by Becquerel to have 

 the cleavage of corundum, and contained small cavities 

 lined with crystals of ruby. Gaudin concluded that 

 alumina could not exist in the vitreous state, and this 

 view was supported by C. Sainte-Claire Deville, on 

 account of the uniform density of the oxide before 

 and after fusion. The facts at' present known are in 

 support of this view, for the transparent alumina 

 obtained by fusion is a completely crvstalline mass. 

 The problem was not further inv'estigated until, in 

 18S6, Charles Friedel described an experiment by which 

 corundum was obtained by fusion, presenting most of 

 the properties of the ruby, but differing from the 

 natural product by the presence of certain included 

 bubbles, and by a rather low density. 



.\s the production of the so-called " Geneva rubies " 

 remained a trade secret, M. Verneuil started a series of 

 investigations, following up the work of Gaudin. He 

 found that to obtain the fused material in a transparent 

 state certain conditions must be rigorously fulfilled. 

 He compares the solidification of alumina to that of 

 water, which forms according to the method of cool- 

 ing transparent or opaque ice. .An important observ- 

 ation which appears to have escaped Gaudin is that it 

 is only the portions of alumina which are fused in the 

 cooler parts of the flame which remain transparent 

 on solidification. One of the greatest experimental 

 difficulties is that, however carefully the cooling is 

 conducted, the fused mass is excessively brittle. This 

 brittleness is least marked when a verv small support- 

 ing surface is employed. The apparatus devised by 

 M. Verneuil is very ingenious. The blow-pipe and 

 furnace tube must be absolutely vertical. The finely 

 powdered alumina, containing the requisite quantity 

 of chromic oxide, and specially purified, is admitted 

 by means of a fine sieve, which is given a series of 

 regular taps, controlled by an electromagnet, so that 

 the material falls down the tube intermittentlv in a 

 series of thin layers. It forms a cone at the bottom, 

 and as soon as this cone reaches a hot enough part of 

 the tube the apex fuses, and the fused mat'erial then 

 extends gradually upwards in a long filament. This 

 eventually reaches a still hotter part of the furnace, and 

 develops a spherical mass instead of growing further; 



■ " Memoire sur la Reproduction artificielle du Rubls par Fusion " By 

 A. Verneuil. (Axnal^s dc CItimiect de Physique, 8' !<rie, t. i!., September.) 



NO. 1834, VOL. 71] 



this spherical globule when solidified forms the ruby. 

 The cooling has to be very gradual, so that the crystal- 

 line particles have time to become regularly arranged, 

 or an opaque product is obtained. If the ovoid mass 

 is carefully detached when cold, it splits up into two 

 nearly equal portions, but not along a cleavage-plane. 

 The product so obtained is an individual crystal, and 

 the direction of its principal optic axis is never very 

 different from that of the major axis of the ovoid. 



The product when cut cannot be distinguished by 

 its chemical, physical, or optical properties from a 

 stone cut from a natural ruby. The operation may 

 be considered successful when the clear product weighs 

 12 to 15 carats, and has a real diameter of 5 or 6 

 millimetres. It is, however, impossible to obtain 

 stones larger than \ carat free from included bubbles 

 and cracks, and experts can therefore readily dis- 

 tinguish the artificial gems from natural ones. These 

 flaws do not in any way detract from the beauty of 

 the stones ; they are often clearer than many natural 

 rubies, which are seldom found perfect. 



The paper is illustrated by diagrams of the very in- 

 genious apparatus devised by the author. 



CALCIUM METAL. 

 ■pLECTROMETALLURGY has at last succeeded 

 -'--' in producing metallic calcium in commercial 

 quantities, and at what must be considered a relatively 

 low price. Until within a few weeks ago this metal 

 had only been available in very small amounts, and re- 

 mained a rare laboratorj' specimen ; it is now obtain- 

 able at a price per kilogram less than that charged 

 by most chemical dealers for a small one-gram sample. 

 Humphry Davy first formed the amalgam by electro- 

 lysing lime, mixed with mercuric oxide and slightly 

 moistened, with a mercury kathode; he isolated the 

 metal in small quantities by distilling off the mercury. 

 Since then many chemists have tried in vain to find 

 a method suitable for its preparation on a larger scale. 

 Matthiesen, making use of Bunsen's suggestion of 

 applying high current density' at the kathode, only 

 succeeded in obtaining a few grams at a time by electro- 

 lysis of the fused chloride, or of mixtures of calcium 

 and other chlorides having a lower fusing point. 

 Henri Moissan, as the result of a critical study of the 

 numerous proposed methods, was able to prepare some- 

 what larger quantities of the metal. His method was 

 essentially a modification of that proposed by Lifes- 

 Bodart and Jobin in 1S5S, which consisted in reducing 

 fused calcium iodide with metallic sodium. Moissan 

 found that molten sodium forms an excellent solvent 

 for calcium, and by heating calcium iodide with a 

 large excess of sodium obtained on cooling a cake 

 of the sodium-calcium alloy resting on the sodium 

 iodide. Small quantities of the alloy were thrown into 

 well cooled absolute alcohol, which reacts with the 

 sodium leaving the calcium pure, but in the state of 

 a fine crystalline powder. This powder can be 

 agglomerated by pressure and fusion, and thus 

 Moissan prepared the fine specimen ingots of this 

 metal which so greatly interested visitors to the Paris 

 Exhibition of iqoo. It is largely to him that we are 

 indebted for a knowledge of the properties of the pure 

 metal, of which he prepared some .1 kilos, bv this 

 process. Contrary to the earlier descriptions, calcium 

 is a white metal, the yellow coloration being due to 

 a film of nitride; its melting point is about 760° C, and 

 its densitv 1-85. The definite compounds which it 

 forms directlv with hydrogen and nitrogen promise 

 useful applications in the laboratory in cases where 

 it is necessary to remove these gases. 



The next advance was made almost simultaneously 

 by Borchers and Stockem at .\ix-ln-Chapelle, and 



