193 Mr. Children's Summary/ Vieio of {March, 



Davy, read his Bakerian Lecture, on some Chemical Agencies of 

 Electricity, before the Royal Society, which was afterwards 

 published in the Philosophical Transactions for the following 

 year. In this celebrated paper, which obtained the prize offered 

 by Napoleon Buonaparte for the best Essay on Voltaic Electri-- 

 city, Sir Humphry Davy clearly promulgated, for the first time, 

 the laws by which the chemical agencies of electricity are regu- 

 lated, and the principles on which their powers of suspending or 

 destroying the usual order of chemical affinities depends. He 

 showed that different elementary substances have different elec- 

 trical energies, some being naturally positive, and others nega- 

 tive, with respect to each other ; and that when a compound, 

 formed of two such elements, is decomposed by the voltaic 

 battery, the body possessing positive energy is repelled by posi- 

 tively electrified surfaces, and attracted by negatively electrical 

 surfaces ; and that the body possessing the negative energy 

 follows the contrary order. 



Adopting these views, Berzelius divides all substances into two 

 great classes, the electro-positive and electro-negative. Simple 

 bodies belonging to the former class, as well as their oxides, 

 always assume the positive state when they meet with other 

 simple bodies or their oxides belonging to the latter; and the 

 oxides of the first class bear the same relation to those of the 

 second, that salifiable bases bear to acids. He considers oxygen 

 as the most electro-negative of all bodies, and the only oi)e 

 whose electrical relations are invariable, it never being positive 

 with respect to any other, and he places it accordingly at the 

 head of his table exhibiting the supposed order of elementary 

 substances with respect to their electrical relations. The last 

 substance in the table, and consequently the most positive, is 

 potassium, and all the intermediate substances between oxygen 

 and that body are considered as negative to all those which 

 stand below them, and positive to all that stand above them in 

 the table. 



Long before any idea had been formed of the electrical rela-- 

 tions of simple combustible bodies, their oxides were divided 

 into acids and bases, the first forming the electro-negative, the 

 second the electro-positive class; amongst the bodies of the 

 first class a weak acid often serves as base to a more powerful 

 acid, and in the electro-positive series, a weak base frequently 

 acts as an acid with respect to one more strongly electro- 

 positive. 



The electrical relations of oxides usually depend on those of 

 their bases; thus an oxide is electro-negative to another oxide, 

 if the base of the former be negative with respect to that of the 

 letter, and vice versa. Sulphuric acid, for instance, is electro- 

 negative with respect to all the metallic oxides, because sulphur 

 is negative with respect to all the metals ; the oxides of potas- 



