90 Dr Stark on the Influence of Colour on Odours. 



is added a positive increase of weight as ascertained by the ba- 

 lance, the conclusions previously drawn from the sense of smell 

 are confirmed in a singular and very satisfactory manner. I 

 have in this mode repeated all the former experiments with dif- 

 ferently coloured substances ; but shall here only detail a few, as 

 sufficient to show the general results : — 



1. I took ten grains of white and the same quantity of black 

 wool, and having suspended them in the manner stated, vaporiz- 

 ed the camphor. When the apparatus cooled, I found, on weigh- 

 ing the wool, that the white had gained l/^ grains in weight, and 

 the black 1 ^^^ grains. 



2. In a similar experiment, but using three colours of wool, 

 white, red, and black, I found the white wool had gained ^% of 

 a grain ; the red j% ; and the black l/g grains. 



3. In another, where the heat was applied for about ten se- 

 conds, the white had gained no appreciable weight, and but little 

 smell ; the red had gained ^\ of a grain ; while the black had 

 acquired /^ of a grain. 



4. In an experiment with black, red, green, and xvhite^ the re- 

 sults were: — 



Black gained in weight f^ of a grain. 

 Green .... ^-^ 



To 



Red ,\ 



White t'5 



5. In an experiment with blacli, blue, green, red, and white, 

 10 grains of each, the result stood thus : — 



Black gained in weight Ij^ of a grain. 



Dark Blue . . . . \^^ 



Scarlet Red .... 1 



Dark Green .... 1 



White 0/5 



In repeating this experiment the dark green was /j, while 

 the red was only -^^ ; the others in the order as before. 



I now varied the experiment by employing square pieces of 

 card of equal size, coloured with different preparations of lead. 

 This was done with the view of ascertaining whether smooth 

 surfaces of equal density, and coloured as nearly as possible with 

 a pigment of the same nature, would absorb odorous particles 

 with the same facihty as loose portions of wool. The colours 



