316 INDUCTION. 



tion on oxygen and hydrogen separately, no knowledge of their laws, could 

 have enabled us deductively to infer that they would produce water. We 

 require a specific experiment on the two combined. 



Under these difficulties, Ave should generally have been indebted for our 

 knowledge of the causes of this class of effects, not to any inquiry direct- 

 ed specifically toward that end, but either to accident, or to the gradual 

 progress of experimentation on the different combinations of which the 

 producing agents are susceptible; if it were not for a peculiarity belonging 

 to effects of this description, that they often, under some particular com- 

 bination of circumstances, reproduce their causes. If water results from 

 the juxtaposition of hydrogen and oxygen whenever this can be made suf- 

 ficiently close and intimate, so, on the other hand, if water itself be placed 

 in certain situations, hydrogen and oxygen are reproduced from it : an 

 abrupt termination is put to the new laws, and the agents re-appear sepa- 

 rately with their own properties as at first. What is called chemical anal- 

 ysis is the process of searching for the causes of a phenomenon among its 

 effects, or rather among the effects produced by the action of some other 

 causes upon it. 



Lavoisier, by heating mercury to a high temperature in a close vessel 

 containing air, found that the mercury increased in weight, and became 

 what was then called red precipitate, while the air, on being examined 

 after the experiment, proved to have lost weight, and to have become in- 

 capable of supporting life or combustion. When red precipitate was ex- 

 posed to a still greater heat, it became mercury again, and gave off a gas 

 which did support life and flame. Thus the agents which by their com- 

 bination produced red precipitate, namely, the mercury and the gas, re- 

 appear as effects resulting from that precipitate when acted upon by heat. 

 So, if we decompose water by means of iron filings, we produce two effects, 

 rust and hydrogen. Now rust is already known, by experiments upon the 

 component substances, to be an effect of the union of iron and oxygen : 

 the iron we ourselves supplied, but the oxygen must have been produced 

 from the water. The result, therefore, is that water has disappeared, and 

 hydrogen and oxygen have appeared in its stead ; or, in other words, the 

 original laws of these gaseous agents, which had been suspended by the 

 superinduction of the new laws called the properties of water, have again 

 started into existence, and the causes of water are found among its effects. 



Where two phenomena, between the laws or properties of which, con- 

 sidered in themselves, no connection can be traced, are thus reciprocally 

 cause and effect, each capable in its turn of being produced from the oth- 

 er, and each, when it produces the other, ceasing itself to exist (as water 

 is produced from oxygen and hydrogen, and oxygen and hydrogen are re- 

 produced from water) ; this causation of the two phenomena by one an- 

 other, each being generated by the other's destruction, is properly trans- 

 formation. The idea of chemical composition is an idea of transformation, 

 but of a transformation which is incomplete; since we consider the oxy- 

 gen and hydrogen to be present in the water as oxygen and hydrogen, and 

 capable of being discovered in it if our senses were sufficiently keen: a 

 supposition (for it is no more) grounded solely on the fact that the weight 

 of the water is the sum of the separate weights of the two ingredients. If 

 there had not been this exception to the entire disappearance, in the com- 

 pound, of the laws of the separate ingredients ; if the combined agents had 

 not, in this one particular of weight, preserved their own laws, and produced 

 a joint result equal to the sum of their separate results ; we should never, 



