THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SEBIES.] 



NOVEMBER 189L 



LII. The Influence of Temperature on the Colour of Pigments 

 By Edward L. Nichols and Benjamin W. Snow*. 



OUR knowledge of the laws which govern the changes of 

 colour which many substances undergo when heated is 

 very incomplete. Certain marked changes of colour which 

 occur under the action of the blowpipe, and which are useful 

 for the identification of the substance exhibiting them, have 

 been noted and described, and some attempts have been made 

 to show that these and other colour-changes follow a general 

 law. 



To Schoenbeinf we owe the general observation that colours 

 grow dark under the action of heat. E. J. Houston J (1871), 

 working in association with Elihu Thomson, studied a great 

 number of substances and noted their change of hue when 

 heated. They stated their conclusion as follows : — " .... the 

 addition of heat causes the colour to pass from one of a greater 

 to one of a less number of vibrations . . . ." 



Ackroyd§ (1876), in a short but admirable paper, con- 

 firmed the observation of a movement of colour-tones " towards 

 the red " upon heating. He supplemented naked-eye obser- 

 vations with spectroscopic study and reached the following 

 result : — " That metachromatism arises from increased ab- 



* Communicated by the Authors, 

 t Pogg-endorff's Annalen, xlv. p. 263. 

 \ Journal of the Franklin Institute, 3rd series, lxii. p. 115. 

 § " Metachromatism, or Colour Change," Chemical News, vol. xxxiv. 

 p. 76. 



Phil. Mag. S. 5. Vol. 32. No. 198. Nov. 1891. 2 E 



