112 CHEMICAL AFFINITY. SECT. XIV, 



the electrical state of the particles of matter. Now it must be 

 observed that the composition of bodies, as well as their decom- 

 position, may be accomplished by means of electricity ; and Dr. 

 Faraday has found that this chemical composition and decompo- 

 sition, by a given current of electricity, is always accomplished 

 according to the laws of definite proportions ; and that the 

 quantity of electricity requisite for the decomposition of a sub- 

 stance is exactly the quantity necessary for its composition. 

 Thus the quantity of electricity which can decompose a grain 

 weight of water is exactly equal to the quantity of electricity 

 which unites the elements of that grain of water together, and is 

 equivalent to the quantity of atmospheric electricity which is 

 active in a very powerful flash of lightning. This law is 

 universal, and of that high and general order which characterises 

 all great discoveries. Chemical force is extremely powerful. A 

 pound of the best coal gives when burnt sufficient heat to raise 

 the temperature of 8086 pounds of water one Centigrade degree, 

 whence Professor Helmholtz of Bonn has computed that the 

 magnitude of the chemical force of attraction between the 

 particles of a pound of coal and the quantity of oxygen that 

 corresponds to it, is capable of lifting a weight of 100 pounds to 

 the height of 20 miles. 



Dr. Faraday has given a singular instance of cohesive force 

 inducing chemical combination, by the following experiment, 

 which seems to be nearly allied to 'the discovery made by M. 

 Doabereiner, in 1823, of the spontaneous combustion of spongy 

 platinum (N. 171) exposed to a stream of hydrogen gas mixed with 

 common air. A plate of platinum with extremely clean surfaces, 

 when plunged into oxygen and hydrogen gas mixed in the pro- 

 portions which are found in the constitution of water, causes the 

 gases to combine and water to be formed, the platinum to become 

 red-hot, and at last an explosion to take place ; the only condi- 

 tions necessary for this curious experiment being excessive 

 purity in the gases and in the surface of the plate. A sufficiently 

 pure metallic surface can only be obtained by immersing the 

 platinum in very strong hot sulphuric acid and then washing it in 

 distilled water, or by making it the positive pole of a galvanic pile 

 in dilute sulphuric acid. It appears that the force of cohesion, aa 

 well as the force of affinity, exerted by particles of matter, extends 

 to all the particles within a very minute distance. Hence the 



