LECTURE V.] HISTORY OF CHEMISTRY. 71 



current into its constituents, hydrogen and oxygen, but that no 

 other kind of change occurs in the water; and that all observa- 

 tions of the apparent occurrence of such change are to be ex- 

 plained either by some action upon the vessel in which the 

 experiment has been conducted, or by some impurity in the 

 water. 



This enquiry is comparable, in many respects, with the first 

 of Lavoisier's investigations. 12 In both cases an endeavour is 

 made to refute a statement based upon inaccurate observation, 

 and that not simply by speculation, or by the assertion that it 

 is in contradiction to general views. In opposition to the 

 earlier superficial experiments, new ones are adduced which 

 have been carried out with the most minute attention to all the 

 conditions. In both cases the purpose is attained, and the 

 older inaccurate view is replaced by a correct one. Such 

 results as those obtained in these cases by Lavoisier and by 

 Davy are often called negative, but most people will agree with 

 me when I assert that they may be of great positive value. 



Davy, however, does not stop here. He next investigates 

 the decomposition of salt solutions, and finds confirmation of 

 the statements of Hisinger and Berzelius. But he proceeds 

 with still greater circumspection, and endeavours to follow up 

 the phenomena more exactly. All the means are at his com- 

 mand, and he does not fail to avail himself of them. 



Direct observation shows Davy that hydrogen, the alkalies, 

 the metals, etc., are separated by means of the current at the 

 negative pole, and oxygen and the acids at the positive pole. 

 From this he concludes that the former substances possess a 

 positive, while oxygen and the acids possess a negative electri- 

 cal energy ; that in this case, as usual, the oppositely electrified 

 bodies attract each other ; and that, in consequence, the posi- 

 tive substances separate at the negative pole, and vice versa. 

 In this assumption Davy had arrived at a conception, or, shall 

 I say, an explanation of the phenomena of decomposition ob- 

 served in the galvanic circuit. But he goes a step further, and 



12 See p. 22, 



