292 



The thanksof the Academy were presented to the Knight 

 of Ghn for his donation. 



Dr. Apjohn read a paper by Dr. Andrews, " on the Heat 

 developed during the Formation of the MetalHc Compounds 

 of Chlorine, Bromine, and Iodine." 



The author confines his attention in the present paper 

 to the combinations of zinc and iron, which metals, he shows, 

 will not combine at ordinary temperatures with chlorine, 

 bromine, or iodine, unless water is also present. The re- 

 actions which take place when an excess of iron in a state of 

 fine subdivision is agitated with any of the three elements 

 just mentioned, are rather complicated, — a sesqui-compound 

 (Fe2Cl3, FegBrg, Fegla) being first formed, which afterwards 

 combines with an additional atom of iron, and becomes con- 

 verted into a proto-compound (Fca CI3, &c.) The heat de- 

 veloped during this process consequently arises from three 

 distinct causes : — first, the union of Fe2 with CI3 ; secondly, 

 the solution of the compound so formed in water; and thirdly, 

 its conversion into Fe^ CI3 by its combination with Fe. The 

 heat arising from the two latter causes being determined by 

 separate experiments, and taken from that obtained during 

 the original reaction, the remainder will be evidently the heat 

 due to the union of Fe2and CI3; and by a similar method, 

 the heat developed during the union of Fe2 with Brs, and of 

 Fe2 with I3, may also be determined. Referred to the num- 

 ber of degrees of Fahrenheit's scale, through which one grain 

 of water would be heated by the combination of one grain of 

 iron in each case, the heat evolved during the formation of 

 Fe2 + CI3 is 3246°; during that of Fe^ + Brg, 2302° ; and of 

 Fe2 -\- 13, 834°. The reaction which occurs when zinc is 

 treated in a similar manner is much simpler, and the heat 

 developed, referred to the zinc as unit, is 276G° for Zn -{- CI ; 

 2284° for Zn -{- Br ; and 1474° for Zn + I. 



The author also proves, by direct experiments, that when 



