INDUSTRIAL PROGRESS DURING THE YEAR 187G. Ivii 



power of light as manifested in the apparatus of Crookes, and comes 

 to the conclusion that the motions observed are due to heat currents 

 produced in the residual air. 



The University of Pennsylvania has recently obtained from Geiss- 

 ler one of Crookes' radiometers. It is extraordinarily delicate, the 

 light of a candle three feet distant causing the vanes to revolve, and 

 the rotation being continuous in ordinary daylight. 



Von Wartha has made a series of experiments on the influence of 

 pressure on combustion. For pressures greater than that of the at- 

 mosphere the experiments were made in the caisson of a bridge 

 crossing the Danube at Buda-Pesth, the manometer there indicating 

 1.95 atmospheres. Six standard candles were burned for a definite 

 time in the open air and then in the caisson, being weighed both be- 

 fore and after each experiment. The result showed the consumption, 

 as a maximum, to be 17.4 per cent, more combustible in air at the or- 

 dinary pressure. In a receiver exhausted to 90 mm. a candle burns 

 with a scarcely visible flame, the cause of which the author believes 

 to be the fact that, as the pressure diminishes, the temperature of 

 dissociation constantly increases. 



Cailletet has also published a j)aper on the influence exerted by 

 pressure on combustion. His experiments were made with a hollow 

 iron cylinder which would stand a pressure of 300 atmospheres, into 

 which air could be compressed by pumps. The flame to be exam- 

 ined was placed in this tube, glasses being inserted in the sides 

 through which it could be seen. A candle flame becomes at first 

 brighter as the pressure increases, but soon smokes, the combustion 

 being incomplete. In general, however, the author concludes that 

 the temperature of combustion increases with the pressure. 



Heumann has published in full his memoir on the theory of lumi- 

 nous flames, in which the results of an extended investigation are 

 given. He maintains that there are three separate causes which 

 may destroy the luminosity of gas subtraction of heat, dilution of 

 the gas, and oxidation of the illuminants. Those hydrocarbon 

 flames which lose their luminosity by cooling them recover it again 

 when they are heated. Those which lose it by dilution with air or 

 with indifferent gases recover it by raising the temperature of tJie 

 flame. Those flames which lose their brightness by the moderate 

 introduction of oxygen, which oxidizes the carbon directly, are made 

 bright again upon diluting the oxygen. 



Champion and Pellet have called attention to the resemblances 

 which exist between the mode of decomposition of explosive bodies 

 and the phenomena of supersaturation. They mention many re- 

 spects, for example, in which a supersaturated solution of sodium 

 sulphate resembles, in its instability and the means by which it 

 solidifies, the explosive dynamite. 



Magnier de la Source has experimented upon the solubility of uric 



3* 



