May 1 6, 1901] 



JVA TURE 



67 



chemists, or how many spoilt lecture experiments may be 

 avoided in future by those who possess a silica tube. 



This last property of silica and the splintering of quartz find 

 an explanation in the results obtained by Le Chatelier {Coinptes 

 «W«^, cviii. 1046, and cxxx. I703)and by Callendar. These, as 

 already explained (Fig. 3), show that its rate of expansion is ex- 

 ceedingly low, and, moreover, that at temperatures much above 

 1000° it contracts when heated. In these circumstances it 

 follows, first, that the strains set up in silica when it is suddenly 

 heated or cooled are comparatively small in amount, and, secondly, 

 that if, for example, vitrified silica be suddenly cooled from 

 1500° to temperatures below 1000°, the strains set up at the 

 earlier stages of the change must tend to neutralise those produced 

 subsequently. These facts enabled Le Chatelier to predict, a 

 little while ago, the indifference of vitrified silica to sudden 

 change of temperature. But the phenomena had been observed 

 previously and exhibited in this country. 



The behaviour of quartz under changes of temperature is also 

 peculiar. This was studied by Le Chatelier in 1889 (Comples 

 rcndiis, cviii. 1046). From his curves, wliich are given in Fig. 3, 

 it may be seen that this form of silica e.spands quite regularly, 

 and much more rapidly than vitreous silica up to 570°, but that 

 at that temperature a sudden expansion takes place which is 

 followed by a steady contraction on further heating. 



One of the most important fields in which vitrified silica is 

 likely to be useful is that of thermometry. 



Owing to the small coefficient of expansion of vitrified silica 

 the degrees of silica-mercury thermometers will be of greater 

 length in proportion to the volumes of the bulbs than those of 



glass instruments. Owing to its high melting point it should be 

 possible to employ it with advantage for measuring high tem- 

 peratures by replacing the mercury by tin or some other metal, 

 as has been done by .\L Dufour (Comptes reiidia, cxxx. 775). 

 And whilst the great elasticity of vitrified silica suggests that the 

 zero points of silica-mercury thermometers will be much more 

 stable than those of glass instruments, the impunity with which 

 it may be suddenly cooled from high temperatures promises 

 obvious advantages. 



Finally, the high melting point of silica should make it very 

 valuable for use in platinum thermometers, and I exhibit such a 

 thermometer to-night which has been fitted up for Dr. R. T. 

 Glazebrook. But as the applications of vitreous silica to ther- 

 mometry are still under investigation I will not dwell on this 

 part of the subject except to add that, as glass reservoirs for 

 air thermometers have proved disappointing, I am not without 

 hopes that the new material may prove helpful in that depart- 

 ment also. 



We have not yet had time to examine the behaviour of silica 

 vrith solvents, but if it acts like other forms of the same com- 

 pound, it may be expected to replace platinum for some 

 purposes, as, for example, for condensers for the preparation of 

 pure water, and vessels of silica probably would be much more 

 suitable for use in exact experiinents on the freezing points and 

 boiling points of many dilute solutions than the glass tubes now 

 often used for such work. But, of course, silica vessels would be 

 very susceptible to the action of alkalis. Finally, silica may be 

 expected to prove superior to glass for use in researches on pure 



NO. 1646, VOL. 64] 



gases, owing to the qualities of its surface, and in experiments 

 concerning the behaviour of gases at high temperatures. We 

 have already one small application of silica to research in this 

 latter field to put upon record. It is well known that nitrogen 

 and oxygen enter into combination under the influence of the 

 silent discharge, and Sir William Crookes ( Chcni. Ncivs, Ixv. 301 ) 

 has shown that oxides of nitrogen are present in considerable 

 quantities in the flames which accompany the electric discharges 

 of large induction coils ; but although various observers have 

 re|iorted indications of the presence of nitrous fumes in the 

 neighbourhood of flames, the forming of an oxide of nitrogen 

 from o.xygen and nitrogen alone, and without the intervention of 

 electricity, has not, so far as 1 am aware, been unmistakably 

 established. Therefore it is interesting to record the fact, first 

 observed by Mr. Lacell, that nitric peroxide may be produced 

 by heating a mixture of oxygen and nitrogen above the melting 

 point of platinum in tubes of silica. It is e.isy to obtain a gas 

 showing a distinctly yellow colour and exhibiting the reactions 

 of nitric peroxide in this way. 



Of course vitreous silica is not entirely without defects. 

 Unfortunately it becomes slightly permeable to hydrogen, as 

 platinum does, though to a less extent (Villard, Comptes rendus, 

 cxxx. 1752), at about 1000°. It is attacked when hot by alkaline 

 oxides. It may be heated to about 960° in contact with copper 

 oxide without injury, but at higher temperatures it is attacked. 

 It may be heated more strongly with ferric oxide, but quicklime 

 attacks it at a bright red heat. It is evident that caution must 

 be exercised when it is employed with basic oxides or alkaline 

 solutions. When one first fashions vessels of silica before the 

 flame the vessels exhibit to a greater or less extent a phenomenon 

 resembling devitrification. They become covered with a white 

 opaque crust. This is easily removed by reheating, provided 

 that the tube has been kept scrupulously free from dust and dirt 

 during the process of making it. If this be not done the ap- 

 pearance of the vessel may be spoilt permanently. The earlier 

 observers attributed this phenomenon to the volatility of silica. 

 My impression is that it is connected with the minute traces of 

 alkalir;e metals present in most Brazil pebble which are usually 

 burnt off in the processes I have described. From what I have 

 told you to-night you will see that in several respects vitrified 

 silica is as much superior to the best glass as Jena glass is 

 superior to more ordinary specimens, and that the progress made 

 in the last few years will make it possible for investigators to 

 employ vitreous silica much more widely in the future than has 

 been possible in the past. At the same time it is evident that 

 the processes for producing vitreous silica are still in their 

 infancy, that there is much more to be done and that further 

 progress can only be made at considerable expense. 



In concluding my remarks I wish to express the great 

 obligation I am under to my friend Mr. Lacell. You will have 

 discovered for yourselves that the chief burden has been upon 

 his shoulders to-night, and that without the illumination pro- 

 vided by his precise and beautiful manipulation my discourse 

 would have been but a dry affair. Also I must add that the 

 cost of the work at its later stages has been aided by a subsidy 

 from the Government Grant Fundoof the Royal Society. 



NOTES FROM RECENT CONSULAR REPORTS. 

 A REPORT on German East Africa, by Mr. A. C. Hollis, 

 ■^ acting vice-consul at Dar-es-Salaam, and one on Veterinary 

 Work in British East Africa and Uganda Protectorates, by Mr. 

 R. J. Stordy, have recently been published as Nos. 2568 and 

 551 of the Foreign Oftice Series. The following notes from the 

 reports refer to matters of scientific interest: — 



German East Africa. 



Locusts. — Great interest was shown in the success of the 

 discoveries made at the Grahamstown Bacteriological Institute 

 in the destruction of these insects, and a small quantity of 

 "locust fungus" was imported, and has since been used on 

 Kilima Njaro and in Usambara with success. 



Caoutdtouc. — There are numerous sorts of caoutchouc creepers 

 and trees indigenous to German East Africa, but the only kinds 

 which are of value are Landolphia Kirkii (Kiswahili, Mohango), 

 and Mascarenhasia elastUa (Kiswahili, M^ora). Until quite 

 lately it was believed that the best rubber was the product of 

 Landolphia fiorida var. Comorensis (Kiswahili, Mhiingo), but it 

 has now been proved that this creeper is practically worthless. 



Samples of the milky juice of the wild fig tree have been sent 



