146 CORRELATION OF PHYSICAL FORCES. 



liquids, or a solid and a liquid, combining and producing a 

 compound which is entirely gaseous at ordinary temperatures 

 and pressures. The substance gun-cotton, however, disco- 

 vered by Schoenbein, very nearly realises this proposition. 



Dr. Andrews has arrived at the conclusion, after careful 

 experiment, that in chemical combinations where acids and 

 alkalies or analogous substances are employed, the amount 

 of heat produced is determined by the basic ingredient, and 

 his experiments have received general assent ; although it 

 should be stated that M. Hess arrived at contrary results, the 

 acid constituent according to his experiments furnishing the 

 measure of the heat developed. 



Light is directly produced by chemical action, as in the 

 flash of gunpowder, the burning of phosphorus in oxygen 

 gas, and all rapid combustions : indeed, wherever intense heat 

 is developed, light accompanies it. In many cases of slow 

 combustion, such as the phenomena of phosphorescence, the 

 light is apparently much more intense than the heat, the 

 former being obvious, the latter so difficult of detection that 

 for a long time it was a question whether any heat was 

 eliminated ; and I am not aware that, at the present day, any 

 thermic effects from certain modes of phosphorescence, such 

 as those of phosphorescent wood, putrescent fish, &c., have 

 been detected. 



Chemical action produces magnetism whenever it is thrown 

 into a definite direction, as in the phenomenon of electrolysis. 

 I may adduce the gas voltaic battery, as presenting a simple 

 instance of the direct production of magnetism by chemical 

 synthesis. Oxygen and hydrogen in that combination chemi- 

 cally unite ; but instead of combining by intimate molecular 

 admixture, as in the ordinary cases, they act upon water, i.e. 

 combined oxygen and hydrogen, placed between them so as 

 to produce a line of chemical action ; and a magnet adja- 

 cent to this line of action is deflected, and places itself at 

 right angles to it. What a chain of molecules does here, there 

 can be no doubt, all the molecules entering into combina- 

 tion would produce in ordinary chemical actions ; but in such 

 cases, the direction of the lines of combination being irregular 

 and confused, there is no general resultant by which the 

 magnet can be affected. 



