ON OUR KNOWLEDGE OF SPECTRUM ANALYSIS. 



317 



diluted to 1 in 50 millions with acetic acid still shows considerable absorp- 

 tion. Hydrocyanic is very diactinic ; cyanuric acid is not, and Prof. 

 Hartley accordingly assigns to it the formula 



HO 



HO^ 



1 li 



HO 



It has been shown that cymene has a well-defined absorption-spectrum, 

 and according to Dr. Armstrong this substance forms a part of orange 

 cil, French turpentine, and Russian turpentine. On examining specimens 

 received from Dr. Armstrong, no cymene could be detected in the first 

 two, and less than 4 per cent, in the last. The inference is, therefore, 

 that the cymene found by Dr. Armstrong was formed by the chemical 

 treatment to which these substances were subjected in his investigation. 



The" wave-length of these cadmium lines is given on p. 299. The light parts indicate the 

 absorbed, and the dark the transmitted, rays. 



J Although there have been but few workers in this line of research, 

 sufficient has been done to indicate its value in investigating the con- 

 stitution of colourless bodies. 



