Spectrum of Silicon as rendered by Silicates. 



Ill 



lengthened when the electrodes are wet.* It is doubtless a carbon line, 

 for Deslandresf gives its wave-length as 4267 (Rowland's unit), and 

 he used carbon purified in Moissan's electric furnace. The least 

 refrangible of the silicon lines on my plates is at wave-length 2881*0, 

 -and it corresponds with a line in the arc spectrum 2881*1 (Liveing 

 and Dewar). 



There is a group of air lines; 4446*02, 4432*58, 4425*90, 4415*51, 

 and 4413*60, then come 4628*95 and 4674*2, but there is no trace of 

 any silicon lines between 4573 and 4553 where Mr. Lunt found three. 



Mr. Lunt used a powerfully disruptive discharge, and that apparently 

 is sufficient to account for the difference in the spectrum which he 

 obtained. I have always employed very simple apparatus, but it 

 happens that when investigating the coefficient of extinction of the 

 various rays of silicon a second series of experiments was made with 

 ■a, more powerful coil and jar. It was found that when all the lines 

 had become very short, and the weaker lines had nearly disappeared, 

 they could be reproduced to a great extent from the same solution by 

 increasing the capacity of the Leyden jar or condenser, but as only 

 extremely dilute solutions of silicates were used, the lines obtained by 

 Mr. Lunt from the solid silicates did not appear. 



I give here the normal length of the six lines in the characteristic 



Silicon Lines. 



A. Strength of solution, or per cent, of silicon. 



B. Length, of the lines in hundredths of an inch. 





Wave- 











Description of lines. 



lengths. 

 (Rowland's 



A, 1-0. 



A, 0-1. 



A, 01. 



A, 001. 





unit.) 



B. 





B. 



B. 



Strongest but one of the 















2506 *8 



20 



10 



10 *0 



9 



A weaker line 



2514 -0 



20 



12 



10 -o 



8 



Strongest and longest .... 



2515 *9 



20 



15 



10 -o 



10 



The weakest' lines of the 



[" 2518-9 

 ■{ 2523-9 



20 

 20 



9 

 10 



7 *5 

 7*5 



7 

 7 



group 



i 2528-6 



20 



10 



7 '5 



7 



An isolated line weak and 















2631 -8 



17 



6 



2 -0 



Barely 

 visible 



Very strong line 



2S81 -5 



22 



14 



10 -o 



9 



* ' Phil. Trans.,' 1884, Part I, p. 49. 



t ' Comptes Rendus,' 1895, vol. 120, p. 1259. 



X These wave-lengths are copied from the original numbers written upon the 

 36-inch enlargements of the spectra referred to as being published in the ' Journal 

 of the Chemical Society.' The values are according to Angstrom's unit, and are 

 doubtless not so accurate as numbers more recently determined. 



