Chemistry and Physics. 365 



explosion-wave and prepare the way for it by ionizing the gas. 

 This problem has been investigated experimentally by Harold B. 

 Dixox, C. Campbell and W. E. Slater. 



The explosive mixtures were detonated by an electric spark in 

 a long tube placed between the pole-pieces of a powerful electro- 

 magnet, which was specially designed for deflecting high-speed 

 electrons. This magnet was loaned to the experimenters by Sir 

 Ernest Rutherford. The explosion-waves characteristic of a 

 given mixture of gases were photographed when the electro- 

 magnet was and was not excited, all other conditions being kept 

 invariable. Preliminary experiments showed, that the /3-rays 

 from radium bromide were completely deflected. The explosive 

 mixtures tested consisted of (a) cyanogen and oxygen with 

 different proportions of nitrogen, (b) hydrogen and oxygen in 

 varying relative amounts, (c) acetylene and oxygen, (d) carbon 

 bisulphide and oxygen, and (e) carbon monoxide and oxygen. 

 In all cases, no difference between the explosion-waves with the 

 magnetic field on and off could be detected. At the end of the 

 article the authors say : " Since the powerful magnetic field 

 employed produced no visible effect with any gas mixture, and 

 since the mechanism of a compression-wave (liberating the chemi- 

 cal energy as it goes along) accounts in a reasonable way for the 

 phenomena of gas explosions, we see no evidence that convinces 

 us that the velocity of the explosion-wave is due to the ionizing 

 action of electrons." In addition to its theoretical value the 

 paper is of interest because of the inclusion in it of excellent 

 reproductions of clear photographs of eight pairs of explosion- 

 waves. — Proc. Roy. Soc, vol. xc (a), p. 506. h. s. it. 



7. The Spectrum of Silicon. — For more than eleven years 

 Sir William Crookes has been making observations on the 

 spark spectrum of elementary silicon, the primary objects of the 

 investigation being (a) to determine precisely what lines pertain 

 to silicon alone, and (b) to determine the wave-lengths of all the 

 lines on a consistent and accurate basis. The spectrum of silicon 

 is of considerable importance in physical astronomy. Great 

 difficulty was encountered in the attempt to obtain perfectly pure 

 silicon. The best specimens were furnished by the Carborundum 

 Company of Niagara Falls. The impurities of these samples 

 were aluminium, iron, and titanium. The apparatus used was a 

 five-prism spectrograph. In order to obtain a photographic 

 record of some of the fainter lines exposures as long as seven 

 hours were necessary. In the visible spectrum the photographic 

 processes were supplemented by eye-observations. The table of 

 wave-lengths contains 43 values and, with two exceptions, each 

 number comprises seven significant figures. In spite of the fact 

 that this piece of work is undoubtedly the most thorough that 

 has been done on the spark spectrum of silicon there is a note- 

 worthy lack of agreement between the wave-lengths of three 

 lines given both by Crookes and by Fabry and Euisson. The 

 interferometer values for silicon, as a carbon-arc impurity, are 



