April 2\, 1 88 7] 



NA TURE 



583 



The Zirconia Oxy-hydrogen Light 



I HAVE been interestetl in tlie brief note you gave upon Prof. 

 Linneniann's zirconia light, and as I have for several years been 

 endeavouring to obtain the alleged advantages of this earth as a 

 liiniinant, and with very different coinparative results, if you 

 will allow me briefly to state these, it may possibly be of service. 

 Zirconia has been stated by Du Motay to be the "most 

 luminous " as well as most refractory of earths, and if it indeed 

 be so, its advantages would be very great. I have made many 

 fniitless attempts to procure c ne of Du Motay's own pencils as 

 prepared and sold many years ago, but none seem now obtain- 

 able ; if any reader possesses, and can lend me, one for trial (all 

 the better if he can share in or witness it), I shall be exceed- 

 ingly obliged, in ihe interests of improved optical projection. 



With the assistance of Mr. Chadwick, of Manchester, Mr. 

 H. G. Madan, of Eton College, and a third gentleman, of 

 Leeds, my own experiments have been made with small cylin- 

 ders about 9 millimetres diameter, compressed from three differ- 

 ent samples of zirconia. The incandescent surface was the Hat 

 end of such a cylinder. 



The first sample was sold as "pure" by Hopkin and Wil- 

 liams, and many cylinders were tried of it. It was very largely 

 contaminated with soda, which might in time have volatilised ; 

 but a more hopeless impurity was the large quantity of silica, 

 which quickly fused into a thick yellow glaze. The light was 

 most inferior, but the reddish tinge presently noticed was 

 not conspicuous in this sample, which was worthless as an 

 illuminant. 



The second sample was prepared by my Leeds colleague, 

 largely by blow-pipe processes. It stood the flame much better, 

 and contained far less soda, which rapidly lessened under the 

 flame. It contained, however, considerable silica, which could 

 be observed through dark glasses to seethe and melt into ridges. 

 When this took place, the light rapidly diminished, and was 

 never near that of a lime cylinder, though at one time respect- 

 able. Also, fissures appeared in the face. But the peculiar 

 physical properties of the earth were conspicuous, and chiefly 

 its extraordinary iton-conuucting power. With a powerful jet 

 (capable of yielding 700 candle-power oa a lime cylinder) play- 

 ing upon the small surface described, the full incandescence 

 barely reached the edge of the disk, and the bright portion only 

 extended about 2J millimetres up the cylinder, bounded by a 

 definite line. .\t this line "a crack all round began to appear, 

 which gradually deepened, until at length the incandescent 

 layer separated and fell off. The glow was of a most pronounced 

 reddish character. 



The third sample was procured by Mr. Madan from Herr 

 Schuchardt, of Gorlitz ; it is stated to be prepared " especially " 

 for the oxy-hydrogen light, and is sold at the rate of 18 marks 

 for 10 grammes, of which about half is required to form a 

 cylinder. This sample shrank enormously when heated, both 

 in powder and when first compressed— showing that it was very 

 largely hydrated — and had to be re-crushed and compressed 

 again before anything could be done with it. It was much 

 more free from silica, and half an hour of a powerful jet only 

 produced a slight glaze or polish on the face. The rcddiih 

 glow was very prominent in it also. The most serious fault, or 

 difliculty, was that the circular crack formed and deepened 

 much more rapidly than in the preceding, and the layer separ- 

 ated in less than half an hour. I fear this unequal shrinkage 

 and its effects will alone be a great obstacle, unless — which I 

 much regret we did not test experimentally — the thin layer itself, 

 as detached, should prove sufficient, held in a platinum loop 

 Possibly it might crack no further. 



But the light was again /.w;- compared with a good lime. Mr. 

 Madan had the plug crushed and re-made, and tested the light 

 photometrically in his own laboratory at Eton. Compared with 

 a good quarr)' lime, the zirconia taken as unity was only i : 2'88, 

 with the same jet. That is a very startling difference. It is 

 true that the incandescent surfaces are probably in about the 

 same proportion, so that the brilliancy /■•;■ unit of surface may 

 be about the same. But then the incandescent surface of the 

 zirconia cannot be increased, owing to the non conducting 

 properties already alluded to ; so that the fact remains, so far as 

 illumination is concerned, that we can only get with zirconia, or 

 with such samples as I was able to obtam, about one-third oii'iie 

 light we can get from a good lime. 



This result is so different from that stated by Prof. Linnemann, 

 and years ago by Du Motay, that some explanation seems neces- 

 sary. I think it lies in the fact that Continental operators do 



not use nearly such powerful jets as are often used in Englan'', 

 where we obtain 600 to 700 candle-power. Several Continental 

 jets have come into my hands, none of which would give a good 

 light, .as a first-class "magic-lantern" lecturer understands it, 

 i.e. sufficient to illuminate a disk 25 feet in diameter. Prof. 

 j Linneniann's own jet, of which I have seen the drawings, 

 I though it has the useftd property of condensing the heat into a 

 very small spot, is only a form of the "blow-through," as 

 usually called ; and when he reniarks upon the "unsteadiness" 

 ' of the mixing jet, he shows that he is not practically acquainted 

 I with it in a good form. Again, I was given by Mr. W G. 

 j Lettsom some time ago a sample of an " improved " composi- 

 I tion sold in Germany instead of limes, and stated to be "much 

 j better " for oxy-hydrogen purposes ; my jets simply burnt holes 

 j clean through it (a prism of about 18 mm. diameter) in less than 

 a minute. Now it is noticeable that with a blow-through jet, of 

 about 200 candle-power, the zirconia does compare much more 

 favourably, and is about as bright as the lime. 

 I I write this, however, with a last hope of getting "more 

 light" on the subject. If we could only get the whole light of 

 a good lime-cylinder into the small disk (which is all that can 

 be heated) of zirconia, the advantage would be very great : the 

 parallel or other beam from the lantern from such a radiant is 

 as sharp as from an arc light, and every Professor knows what 

 that means. 700 candle-power without trouble — who does not 

 long for it? It will be observed that each of the three samples 

 described behaved differently, and it is in this fact lies my chief 

 hope of any success yet ; otherwise it is the decided opinion of 

 all who have shared in these experiments, that the vaunted zir- 

 conia light is a sheer delusion. If any reader of these columns 

 knows of purer samples to be procured commercially (I know 

 Draper's process, but am no practical chemist, and have neither 

 time nor means to prepare samples myself) ; or can tell me if the 

 peculiar rci/ ^/ow noticed is characteristic of the earth itself or 

 of some impurity ; or has tested lanthana or any other of the 

 more refractory earths ; or can in any way assist me in what is, 

 in its way, a matter of some importance to the science lectu' e- 

 room, I shall feel much obliged for any communication from 

 him, either here, or to Lewis Wright 



7 Beaumont Road, Hornsey Rise, N. 



The Production of Newton's Rings by Plane Soap- 

 Films 



Lord Rayleigh, in his recent lecture at the Royal Institu- 

 tion on "The Colours of Thin Plates," introduced -Sir D. 

 Brewster's experiment, in which circular rings instead of the 

 usual straight bands are produced in a vertical soap-film by 

 causing a jet of air to impinge very obliquely upon the film near 

 its edge. The particles are thus thrown into a vortex- motion, 

 and the centrifugal tendency causes the film to become thinner 

 at the centre than at the edge, so as to produce very fair rings 

 of colour. 



Perhaps it may be worth mentioning that the same effect 

 may be produced with greater regularity and less risk to the 

 film, by giving the ring to which it is attached a rapid move- 

 ment of rotation in its own plane. .\ shallow brass cup, about 8 

 or 9 cm. in diameter, the edge of which is turned inwards and 

 rounded so as to give it the following section, 

 is mounted on a horizontal spindle so that it can 

 be turned rapidly in a vertical plane (any ordinary 

 smooth-running multiplying-wheel arrangement 

 will answer, but a small electromotor is by far 

 the most convenient). The edge of the cup is 

 just dipped below the surface of the soap-solu- 

 tion, and then the socket at the b.ack is 

 fitted on the spindle and rotation commenced. At first the 

 straight horizontal bands of colour maintain their form and 

 position, for the reason which Lord Rayleigh well explained ; 

 but, as the speed increases, the adhesion of the film to the edge 

 of the cup, and the cohesion of its particles, cause it to take up 

 gradually the motion of the cup ; and, as the mass accumulates 

 at the circumference, very perfect circular rings are formed, 

 which can be projected with brilliancy on a screen by the 

 lime-light. II. G. Mada.n 



Eton College 



Barnard's Second Comet 



There would appear to be some danger that the observation 



of the above comet may be relinquished rather prematurely, as 



