Dr Stark o?i the Influence of Colour on Odours. 89 



from the animal, vegetable, or mineral kingdom. My aim is 

 only to show, that odours, like heat and dew, are influenced by 

 colour, and that the same laws which regulate the absorption 

 and radiation of heat and light, may be apphed with equal pro* 

 priety to the imbibition and emission of odorous particles. 



My first experiments on odours, made some years ago, were 

 with articles submitted to the action of odorous substances, by 

 being inclosed with them in drawers or boxes for a certain pe- 

 riod, and the amount of attraction ascertained by the intensity 

 of smell. In all these experiments, however, reliance had to be 

 placed upon one sense alone, viz. that of smell, as none of the 

 substances employed had gained any appreciable weight. I was 

 therefore desirous that, if possible, at least one experiment should 

 be devised, which would show, by actual increase of weight, that 

 one colour invariably attracted more of any odorous substance 

 than another ; and upon considering the various odorous sub- 

 stances which could beeasily volatilized without change, and whose 

 odour was inseparable from the substance, I fixed upon camphor 

 as the one best suited to my purpose. In an experiment of 

 this nature, it was necessary that the camphor should be vola- 

 tilized or converted into vapour, and that the coloured substance 

 should be so placed as to come in contact with the camphor 

 while in that state. It was therefore of the first importance to 

 prevent currents of air within the vessel in which the experiment 

 was conducted, and with this view I used a funnel-shaped vessel 

 of tin-plate, open at top and bottom. This rested on a plate of 

 sheet iron, in the centre of which the camphor to be volatilized 

 was placed. The coloured substances, after being accurately 

 weighed, were then supported on a bent wire, and introduced 

 through the upper aperture. This was then covered over with 

 a plate of glass. Heat was now applied gently to volatilize the 

 camphor ; and when the heat was withdrawn, and the apparatus 

 cool, the coloured substances were again accurately weighed, and 

 the difference in weight noted down. 



Proceeding on this plan, I arrived at the most satisfactory 

 and conclusive results. The deposition of the camphor in va- 

 rious proportions on the coloured substances submitted to expe- 

 riment, offered evidence of the particular attraction of colour 

 for odours, resting on ocular demonstration ; and when to this 



