306 



Finally, zincethyl is decomposed by water into oxide of zinc and 

 hydride of ethyl 



C 4 H 5 Zn-| fC 4 H 5 H 

 H O J ~~ I Zn O. 



It is also similarly acted upon by the hydrated acids and by the 

 hydrogen compounds of chlorine, bromine, iodine, fluorine and 

 sulphur. 



The behaviour of zincethyl in contact with the electro-negative 

 elements is highly remarkable, and cannot fail to have an important 

 influence upon our views of the condition of bodies at the moment of 

 chemical change, a subject so ably discussed by Brodie*, whose in- 

 genious views I consider to receive a new support in these reactions 

 of zincethyl, by the singular way in which ethyl, a body low down 

 in the electro-positive series, unites with oxygen, chlorine, &c., in 

 the presence of a large excess of the intensely electro-positive zinc- 

 ethyl. This behaviour also strikingly confirms the suggestions I 

 ventured to make in my former memoir f, relative to the moleculo- 

 symmetrical form of organo -metallic compounds. In the inorganic 

 combinations of zinc, this metal unites with one atom only of other 

 elements ; a very unstable peroxide, not hitherto isolated, being the 

 only exception. The atom of zinc appears, therefore, to have only 

 one point of attraction, and hence, notwithstanding the intense 

 affinities of its compound with ethyl, any union with a second body 

 is necessarily attended by the expulsion of the ethyl. 



II. "Note on the Magnetic Medium." By Prof. A. W. WIL- 

 LIAMSON. Communicated by Dr. SHARPEY, Sec. R.S. 

 Received March 15, 1855. 



In a letter to Mr. Faraday recently published in the Philosophical 

 Magazine, Dr. Tyndall brings forward some important considera- 

 tions on the subject of magnetic philosophy. 



It has been known for some time that the phenomena of dia- 

 magnetism may be produced artificially in bodies which are usually 



* Philosophical Transactions, 1850, p. 789. f Ibid. 1852, p. 438. 



