502 SCIENTIFIC! PIECOIID FOR ibcD. 



is preferable ; while above 430 atuiosplieres bydrogeu is preferable, 

 the curve of i)V being a straight lino for this gas. (C. B., xcix, 1017 ; 

 FIdl. Mag., February, 1885, V, xix, 150.) 



Bottomley has communicated to the Royal Society a preliminary note 

 on the condensation of gases at the surface of glass. A quantity of 

 non-tubular spun glass was placed in a glass tube which was then ex- 

 hausted with a Spreugel ])ump til! the exhaustion, as shown by the Mac- 

 Leod gauge, was three ten-milliouths of an atmosphere. At the end of 

 an hour the vacuum remained sensibly the same, the temperature of the 

 room being about 14°. While the mercury was flowing through for the 

 third time the tube containing the glass was heated with a Bunsen 

 flame. The hammering produced by the falling mercury at once ceased 

 aud tlie MacLeod gauge showed a considerable increase of pressure. The 

 action of the pump was continued, and the temperature raised as high 

 as the tube would bear in order to remove all the adhering gas. The 

 collecting tube was then removed and the gas contained in it analyzed. 

 The quantity was only 0-45°- "• and it consisted of carbon dioxide 8-24 

 per cent., oxygen 22*76 per cent., and nitrogen 69 per cent. The fibers 

 of the spun glass were measured and found to be fairly uniform aud 7-0(3 

 hundredths of a millimeter in average diameter. By comparative 

 weighing the number of fibers in the tube was found to be 6,370. Their 

 average length was 10-25"". Hence their total surface was l,448«<i- <"". 

 In a second experiment 15,500 glass fibers were used, having a total 

 surface of 3,527«i- *=■". The gas given off" measured 0-41« « of which 78-6 

 per cent, was carbon dioxide, the remainder being oxygen (10-5 per 

 cent.) and nitrogen (89-5 per cent.). This large amount of carbon di- 

 oxide is difficult to account for unless it was taken up by the glass at 

 the time it was spun. {Nature, March, 1885, xxxi, 423.) 



Kayser, in a note to the Physical Society of Berlin, calls attention to 

 Bunsen's paper explaining the discrepancies between his own results 

 and those of Kayser regarding the absorption of carbon dioxide by glass 

 surfaces. Bunsen has now shown that the glass threads, even after dry 

 air had been passed over them for a long time, still retained a layer of 

 water which was thinner the higher the temperature, but was not entirely 

 dissipated until the temperature reached 500^. Hence the absorption 

 observed by Bunsen, and which appeared to continue indefinitely, would 

 seem to have been an absorption by this layer of water, whereas in 

 Kayser's experiments, in which the glass threads had been freed from all 

 adhering matters by boiling oil, the carbon dioxide had been absorbed 

 by the smooth glass itself. {Nature, May, 1885, xxxir, 72.) 



ACOUSTICS. 



Neyreneuf has determined the velocity of sound in steam by a method 

 based upon certain observations of Weber and Savart. A longitudi- 

 nally vibrating reed is attached to the end of a cylindrical draw-tube 

 3-8""" in diameter through which the air passes to tJirow it into vibra- 



