SO'i Dvi. Ai^BVLBWs on the Heat developed during the Formation of the 



The relative proportion of water is also a matter of importance. The quantity 

 present must be suflScient to dissolve, with facility, the resulting compound, and 

 it ought not greatly to exceed that amount. In the following experiments I 

 usually employed about 2.4 gr. of water, for every 0.42 gr. chlorine, 0.9 gr. bro- 

 mine, and 1.5 gr. iodine, which entered into combination. If this precaution be 

 attended to, and the mixture briskly agitated, the whole reaction will be com- 

 pleted in the course of a few seconds. 



3. As our object is to ascertain the heat due to the combination of the re- 

 acting bodies in an anhydrous state, and as we actually obtain the result of the 

 combination In a state of solution in water, It is obviously necessary, in the first 

 instance, to apply a correction for the heat arising from the solution. The 

 amount of this correction is easily discovered, by determining the heat evolved 

 during the solution of a corresponding weight of the dry compound in the nor- 

 mal proportion of water. If the combining bodies do not unite in more than 

 one proportion, there only now remains to be determined the heat evolved or 

 absorbed during the changes of aggregation which occur in the course of the 

 combination. Unfortunately we cannot attempt, by direct experiments, to dis- 

 cover the amount of this Important correction. 



4. If we now make 



A := heat evolved during the reaction of chlorine, zinc (in excess), and 



water, 

 B zz heat evolved during the solution of Zn CI in a like proportion of 



water, 

 X = heat evolved or absorbed during the change of the constituents 



its oxide by means of hydrogen gas, although the action, as is well known, is most energetic if mois- 

 ture be present. On the contrary, the dry gas instantly combines with arsenic, antimony, and phos- 

 phorus. This striking difference appears to depend upon the circumstance that the compound* 

 formed by chlorine with the former substances are solid at common temperatures and very fixed, 

 while those formed with antimony and arsenic are fluid and volatile. The chloride of phosphorus 

 is also very volatile. If, however, the chemical affinity be very intense, combination will take place 

 although the resulting compound be quite fixed and solid. Thus potassium inflames in dry chlorine 

 gas, but the chloride which is formed terminates the action before the whole of the metal has entered 

 into combination. The fluidity of the metal also exercises an important influence in determining 

 the combination, — as in the case of mercury, which slowly combines with dry chlorine. The pre- 

 ceding remarks may be also applied to the behaviour of dry bromine when brought into contact 

 with the metals. 



