100 Proceedings of the British Association. 



many others of a similiar class, whose properties I am at present inves- 

 tigating. The circumstances which led me to enter into these experi- 

 ments, were to remove the objections which the opponents of isomorphism 

 have urged against that theory, on account of the great dissimilarity, 

 both in chemical and in physical characters, which exists between the 

 chromates and their corresponding sulphates. By boiling a sulphate of 

 the oxide required with chromate of barytes, soluble salts may be ob- 

 tained, isomorphous with the sulphates, and, in general, affecting the 

 same number of atoms of water. The insoluble chromates, generally 

 described in systematic treaties on chemistry as neutral chromates, are of 

 a very interesting constitution, but their analytical developement is ex- 

 tremely intricate, from the fact of there being several of each oxide. 

 There are many other points connected with this subject, with which I 

 cannot detain you.* 



' A new theory of the Galvanization of Metals,' by Prof. Schonbein, 

 of Basle. — The Professor began by stating, that the discovery of the 

 chemical power of the voltaic pile, made in the beginning of the present 

 century by British philosophers, drew the attention of the scientific 

 world to the relations which exist between chemical and electrical phe- 

 nomena ; indeed, only a few years after this important fact had been 

 ascertained, Sir Humphry Davy and Berzelius did not hesitate to esta- 

 blish the theory which has since been generally adopted — viz. that che- 

 mical and electrical forces are essentially the same. Prof. Schonbein 

 considers, that the results of recent experiments are opposed to the 

 theory. The facts which he brings forward in opposition to it are as 

 follows : — 1. A piece of iron was voltaically associated with a piece of 

 zinc, and each of these metals was put into a separate vessel, filled with 

 common water. The vessels did not communicate with each other. In 

 the course of a few hours after the immersion of the iron, light flakes of 

 oxide of iron made their appearance round the metal, and, after a cou- 

 ple of days, the latter was corroded to a considerable degree. The same 

 result was obtained when the iron was plunged into water, and the zinc 

 made to rise above the level of the fluid, so as to prevent the latter from 

 being in the least contact with water. According to Prof. Schonbein, 

 a piece of iron, when immersed in water without any voltaic associa- 

 tion, was as much corroded as under the circumstances detailed. 2. Two 

 pieces of iron were made, one of them the positive, the other the nega- 

 tive pole of a voltaic pile, which consisted of ten pairs of copper and 

 zinc, and was charged with water holding 5 per cent, of common salt in 

 solution. Each of the polar wires was put in a separate vessel, filled 

 with common water. Under these circumstances, both wires were 

 equally attacked and corroded in the same manner as if a single piece of 



* The young chemist whose name is already associated with original researches came to 

 Calcutta in 1838, but was induced to return by the same ship that brought him out. Europe 

 undoubtedly presents a wider field to philosophical minds, but settle where he may, Mr. Playfair 

 will rise to the first eminence in his profession. 



