208 



gives an account of the results of his experiments to determine its 

 solubility at different temperatures. He next proceeds to consider 

 the bicarbonate of ammonia, which he finds to consist of one propor- 

 tion of ammonia, two of carbonic acid, and two of water. He con- 

 cludes by an inquiry into the effects of heat on the solid sesquicar- 

 bonate and the carbonate of ammonia, in which he reviews the ex- 

 periments and inferences which Sir H. Davy has recorded in his ma- 

 nuscript notes. 



5. " On the Influence of Colour on Heat and Odours." By James 

 Stark, M.D., of Edinburgh. Communicated by Sir David Brewster, 

 K.H., LL.D., F.R.S. V.P.R.S.Ed. 



The author observes, that the only experiments on record relating 

 to the modifying effect of different colours on the absorption of heat 

 from solar light, are those of Franklin and of Sir H. Davy. In order 

 to investigate this subject, the author employed pieces of wool, silk, 

 and cotton, which were wrapped round the bulb of a thermometer 

 placed in a glass tube : the tube was then plunged into boiling water, 

 and the time which elapsed during the rise of the thermometer from 

 one given point to another was accurately noted. Other experiments 

 were also made with an air-thermometer, of which the bulb was coated 

 with various coloured materials, and heat thrown on the ball by means 

 of polished tin reflectors from an Argand burner. The results accord 

 very nearly with those of Franklin and of Davy j the absorbing power 

 with regard to different colours being nearly uniformly in the order of 

 black, brown, green, red, yellow, and white. The author next investi- 

 gates the differences which occur in the radiation of heat by differently 

 coloured substances ; a subject on which he is not aware that any ex- 

 periments have ever been made previously to his own. The mode of 

 ascertaining the amount of radiation was generally the converse of 

 that by which the absorption of heat had been determined j namely, 

 by exposing the coloured substances, in contact with a thermometer, 

 to cooling instead of heating processes. The general result of all his 

 experiments was, that the loss of caloric by radiation follows exactly 

 the same order, with regard to the colour of the radiating surface, as 

 its absorption. 



In the second part of his paper the author gives an account of a 

 course of experiments which he made with a view to discover the in- 

 fluence of colour on the absorption of odorous effluvia, and more espe- 

 cially in the case of the absorption of the fumes of camphor and assa- 

 fcetida by woollen cloth of different colours. Black cloth was always 

 found to be possessed of the greatest absorbing powers, and white of 

 the least ; red cloth being intermediate between them. Cottons and 

 silks gave, on trial, precisely the same results, which were further 

 confirmed by the different weights acquired by these substances from 

 the deposition of camphor upon them. 



