On the Heat disengaged during Combination. 427 



nation, which was such that no glass vessel could resist it 

 without breaking. Having formei'ly observed that chlorine 

 gas, if perfectly dry, has not the slightest action in the cold on 

 copper or zinc, it occurred to me that the experiment might 

 perhaps succeed, if a brass vessel were substituted for the glass 

 one to contain the chlorine. On making the trial with the 

 requisite precautions, it succeeded perfectly. The chlorine 

 must, however, be dried with the greatest care, and the lid of the 

 brass vessel closed by ground metallic surfaces without the inter- 

 position of leather. The apparatus is represented in Plate III. 

 fig. 6. The lid b has attached to it two copper tubes, by means 

 of which the vessel is filled with chlorine. It is fixed in its place 

 by means of the coupling screw c. As soon as the air has been 

 swept away by the current of chlorine, the ends of the copper 

 tubes are closed by small pins of the same metal, which are 

 secured in their places by caoutchouc covers. While filling 

 the brass vessel with gas, two similar glass vessels were con- 

 nected with it, one on each side, so as to be filled by the 

 same stream of gas; and the purity of the chlorine contained 

 in the intermediate brass vessel was ascertained by analysing 

 the gas in the other two vessels. 



The combining substance was in all cases employed in con- 

 siderable excess ; and from the constant agitation, the whole 

 of the chlorine entered into combination in the course of a 

 very short time. 



The formula deduced from direct observation to express 

 the correction required in this apparatus for the heating and 

 cooling influence of the air, during ju minutes {a, as before, 

 being the difference between the temperature of the apparatus 

 and of the air), was the following: 



V=+w(f/ + 0'-5).0"-01. 

 In applying this formula, it was assumed that the apparatus 

 was at the initial temperature during one minute, and at the 

 final temperature during three minutes. 



Potassium and Chlorine. 



In the following tables, M designates the volume of chlo- 

 rine (dry) in cubic centimetres. 



