-.8o 



NATURE. 



February 20, 1896 



wise precisely alike. A comparison of these should show 

 whether the foreign object is nearer the dorsal or the plantar 

 aspect of the foot. 



" The second point refers to the three objects not seen clearly 

 in the radiogram. The tube used was the ordinary ' shadow of 

 the cross' one, and, though the cross was bent back, the 

 shadow of its supports was visible ; two of the objects were 

 directly under this shadow. The third lay parallel and very 

 close to a bone, and hence is not plainly distinguishable." 



Photographs have been obtained by utilising other sources of 

 luminosity than high vacuum tubes. The following experiments, 

 performed by Messrs. Wm. Wallace and H. C. Pocklington in 

 the Physical Laboratory of the Leeds Central Higher Grade 

 School, are of interest : — 



"A cheap German incandescent lamp of low candle-power 

 was used in place of a Crookes' tube, a piece of tinfoil applied 

 to the outside serving as one electrode, and the filament as the 

 other. The current employed was the high frequency one 

 obtained from a Tesla coil actuated by a large Ruhmkorff. The 

 sparking distance of the Tesla was about 5/8 inch. This appa- 

 ratus gave a vivid green phosphorescence of the glass, which 

 soon grew less, and in fifteen minutes had almost disappeared. 

 Three exposures were made in succession, each of fifteen 

 minutes : the first when the lamp was new ; the second imme- 

 diately afterwards, the lamp being tired by the previous 

 exposure ; for the third, the tinfoil electrode was shifted round 

 about 90°, so as to utilise a fresh part ©f the surface of the 

 glass. The three negatives were developed simultaneously ; 

 the first was good, the other two were under-exposed to about 

 the same extent. In the last experiment, the green phosphor- 

 escence, though not as brilliant as in the first, was much more 

 brilliant than in the second. This seems to show that the pro- 

 duction of X-rays is due to some cause different from that which 

 produces the phosphorescence." 



Mr. J. W. Gifford has obtained photographs by Rontgen's 

 methods, and also by means of the ordinary discharge of an in- 

 duction coil. Replying to a suggestion that results obtained by 

 him with metal discs were due to a " contact " phenomenon, and 

 not to Rontgen's rays, he says : — 



"I notice in your issue of February 13, p. 340, that Mr. 

 Sydney D. Rowland thinks that he has evidence to prove that 

 my results without a Crookes' tube were not due to the 

 ' Rontgen rays.' I have already replied to his observations 

 elsewhere {British Medical yoitriial) ; but will you allow me to 

 say that I think the evidence he advances entirely turns on 

 whether the electrograph was a shadow or an impression, or, 

 in other words, whether surface markings of the objects electro- 

 graphed were reproduced, or not. Now, the discs I used bore 

 numbers stamped on them, but in no case were these numbers, 

 or any surface markings whatever, to be found in the resulting 

 negative, a print of which I enclose. 



" With regard to what Mr. Rowland says about the objects, in 

 his case, being behind or in front of the film, I would suggest 

 that the discharge from a coil is an oscillatory one, and that 

 glass is fairly transparent to the ' Rontgen rays,' almost as 

 transparent as aluminium, in fact. But conditions are often so 

 different, that I do not feel justified in criticising another man's 

 work without having seen his experiments myself I must, 

 however, most emphatically disclaim any positive assertions in 

 the present stage of the inquiry. I have, as far as I am aware, 

 only mentioned tentatively what seem to me the general indica- 

 tions of my experiments up to now, and feel that in investiga- 

 tions of this kind the balance is generally in favour of one's 

 first impressions being wrong. 



" I do not know if you have observed that when Crookes' tubes 

 are employed for the purpose, after about an hour's use they 

 become coated, both above and below, with a thin layer of dust. 

 This happens, at least, time after time in my own laboratory." 



Mr. W. A. D. Rudge, writing from the Science, Art and 

 Technical Schools, Plymouth, says that he has obtained a 

 radiogram of a crayfish, and found the exoskeleton to be as 

 transparent to the new radiations as glass and aluminium. 



Our United States correspondent sends us descriptions of 

 work being done in America, in continuation of Rontgen's 

 discovery. He says very successful photographs have now 

 been obtained by Prof. A. W. Wright, of Yale. Prof Wright 

 has photographed a piece of metal having a fracture which 

 had been welded, but showed no flaw or line of puncture 

 to the eye. The photograph, however, revealed the fracture. 

 Thistlast result was considered by ordnance officials of the 



NO. 1373, VOL. 53] 



Government to be of profound significance, as indicating a 

 means of testing armour for hidden defects and discovering 

 hidden flaws in machinery. Prof. John Trowbridge, of Cam- 

 bridge, Mass., has also obtained some results. He arranged 

 strips of glass an eighth inch thick in a wooden box of inch 

 board, and passed the rays through the board, thus obtaining a 

 photograph of the strips of glass. By passing the rays through 

 prisms of wood and of vulcanite he has confirmed the observation 

 that they were not refracted. 



THE MANUFACTURE OF ALUMINIUM BY 



ELECTROL YSIS. 

 A T the ordinary meeting of the Institution of Civil Engineers 

 on Tuesday, February 11, a paper was read on "The 

 Manufacture of .Aluminium by Electrolysis, and the Plant at 

 Niagara for its Extraction," by Mr. Alfred E. Hunt. The 

 author's description of the ores of aluminium best fitted for 

 electrolytic reduction to the metallic state, and of the general 

 principles governing the extraction of the metal from its 

 compounds, makes interesting reading. 



The Hall process, which is that adopted by the Pittsburg 

 Reduction Company, involves the direct electrolysis of the 

 sesquioxide, alumina, dissolved in a molten bath of the mixed 

 fluorides of aluminium, calcium and sodium. One cubic foot of 

 the solvent serves for an hourly production of one pound of 

 metallic aluminium, the bath used being capable of dissolving 

 one-third of its own weight of alumina. The electrical energy 

 required for extracting this amount of metal is 3730 watt-hours 

 for the decomposition of the alumina, with a further supply to 

 maintain the bath at the temperature necessary for the molten 

 condition. The fluorides remain unchanged, so that the 

 operation is continuous. The bath is made either from a mixture 

 of fluorspar and cryolite, or from the artificial fluorides ; and it 

 may be fused in a separate vessel when starting work, or in the 

 bath by the current itself. Alumina is added at frequent intervals 

 to prevent too great a variation in the resistance of the bath, and 

 the aluminium, as it is produced, is siphoned from beneath the 

 layer of fluoride, where it collected, without interference with 

 the progress of the operations. The oxygen of the alumina is 

 liberated at the carbon anode, which, at the temperature of the 

 bath (980° C. ) oxidises to carbon monoxide. Outside the bath 

 this is burnt at once to carbon dioxide, and is allowed to escape 

 into the working apartment. The carbon anodes are consumed 

 at nearly the same rate as the aluminium is produced, the amount 

 being about two-thirds of the quantity actually used. The 

 difference of potentials theoretically necessary for the separation 

 of the constituents of alumina is about 2 '8 volts, but a greater 

 difference is due to the resistance of the bath. The pots 

 employed are of iron with carbon linings, but these can be 

 dispensed with if a high degree of purity is not required. 



The chief impurities in the finished product are silicon and 

 iron. These are derived from the alumina as well as from the 

 carbon anodes. Aluminium can be produced containing 99^ 

 per cent, of the pure metal, and is regularly delivered with 

 99 per cent. The electrolytic baths are joined in series, the 

 positive bar of the switch-board being joined to the carbon 

 anode of one of the baths, and the last pot of the series being 

 joined to the negative board of the switch-board. All the copper 

 connections are necessarily very heavy, on account of the large 

 currents employed. 



The electrical energy is generated at the works of the Niagara 

 Falls Power Company, and is conveyed, without the intervention 

 of transformers, over a distance of about half a mile, by stranded 

 copper cables \\ inches in diameter. The loss in transmission is 

 about i^ per cent, of the energy conveyed. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Oxford. — Mr. D. H. Nagel, Fellow of Trinity College, has 

 been elected as a Delegate of Local Examinations in place of 

 Mr. E. Chapman, Fellow of Magdalen College, resigned. 



Mr. F. T. Richards, Fellow of Trinity College, has been re- 

 elected a Curator of the Botanic Garden. 



Mr. J. E. Marsh, M.A. , Balliol College, has been reappointed 

 Lecturer in Materia Medica and Pharmacology for the year 

 1896. 



