78 Dr Stark on the Influence of Colour on Heat. 



Black wool fell from 180° to 50° Fahr. in . 21' 0" 



Red, . . . . . . 26 



White, . . . . . . 27 



Another experiment with black, red, and white wools, twenty 

 grains of each, and with the temperature raised to 173°, gave 

 the following results : 



Black wool fell from 170" to 60° Fahr. in . 15' 45" 



Red, 17 



\Vhite, 18 30 



The next experiments were made with wheat-flour, coloured 

 black, brown, yellow, and white. The black colouring matter 

 was lamp-black ; the brown was the umber of the shops ; and 

 gamboge powder was the yellow. I took 100 grains of each 

 coloured flour, and placed them separately in a tube of about 

 three quarters of an inch in diameter, then sunk the bulb of the 

 thermometer into the middle of the flour, and heated the tube 

 to about 190° Fahr. When the mercury began steadily to de- 

 scend, and arrived at 180°, I plunged the tube into water at 45% 

 and observed the rate of cooling. The following were the re- 

 sults : 



Black flour fell from 180' to 50° Fahr. in . 9' 50'' 



Brown, . . . . . 11 



Yellow, 12 



White, . . . . . 12 15 



A third set of experiments was made by coating the ball of 

 the air-thermometer with various pigments ; but for these I must 

 refer to the paper alluded to *. 



These experiments demonstrate, that differently coloured sub- 

 stances possess a specific influence on the absorption of heat or 

 caloric, both luminous and non-luminous, and that they give off" 

 their caloric in the same ratio as they absorb it. 



The experiments may be varied to any extent, by using dif- 

 ferent substances ; and even water in coloured vessels cools more 

 or less quickly, according to the colour of the vessel in which 

 it is held. For instance, to ascertain this, I filled glass balls 

 about an inch and a quarter in diameter with water at 120° Fahr. 

 and placed a thermometer in the fluid. The time which elapsed 

 during the fall of the mercury through 25° was accurately noted ; 

 and the results were, that the ball coated with Prussian blue 

 fell through that interval in seventeen minutes ; the ball coated 

 • PhiL Trans. 1833, p. 294, et seq. 



