EXPERIMENTAL DETAILS. 305 



trated but not saturated ; then we place in the same cylinder a 

 glass phial containing 1*591 grm. of absolutely pure hydro- 

 cyanic acid the phial itself weighs 1*568 grm. it is very thin 

 and elongated into a point at each end, so as to be easily 

 broken when the cylinder is shaken. 



These operations having been quickly performed, and the 

 phial being sealed, the cylinder is corked up, and the calori- 

 metric thermometer observed during an interval of ten minutes. 

 There was absolutely no variation during this interval in the 

 experiment performed. The temperature was about 20. 



First stage. After the preliminary operations, we raise the 

 platinum cylinder a little by means of a pair of wooden pincers, 

 without, however, drawing it entirely out of the water, and 

 shake it violently so as to break the phial. It is then plunged 

 immediately into the calorimeter, and the course of the thermo- 

 meter again observed at the end of each minute. Eeaction 

 takes place, and the heat given off is gradually absorbed by 

 the water of the calorimeter. The variation of temperature is 

 most rapid at the commencement, but the maximum tempera- 

 ture is not produced until after a considerable length of time. 

 It exceeds the original by + 1'3. It lasts for a quarter of 

 an hour and then the temperature slowly falls. We follow 

 this cooling for forty minutes, during which interval it only 

 amounts to 0*17 of a degree. This is the first stage of the 

 experiment. 



Second stage. We next incline the platinum cylinder and 

 open it under the water of the calorimeter, so as to fill it ; the 

 contents of the cylinder are mixed with those of the calorimeter 

 by stirring, until the thermometer, on being plunged alternately 

 into the calorimeter and cylinder, indicates exactly the same 

 temperature. This is the second stage of the operation. It 

 lasts about a minute, and gives rise to an excess of -f- 1*5 over 

 the temperature of the calorimeter at the beginning of this 

 stage, or -f 2-6 over the temperature at the beginning of the 

 entire experiment, i.e. at the beginning of the first stage. The 

 rate of cooling during an interval of five minutes is then 

 observed and the experiment is ended. 



Verifications. We then make sure, by means of suitable 

 reactions (the formation of Prussian blue), that the liquid 

 contains no appreciable quantity of hydrocyanic acid the 

 latter having been entirely converted into formic acid and 

 ammonium chloride. 



Moreover, in order to calculate the rate of cooling during 

 the first stage of the experiment, we proceed, by the addition 

 or subtraction of suitable quantities of water, to bring 

 the temperature of the liquid contained in the calorimeter 

 (the mass of water being kept constant during these fresh 

 mixtures) to + 1*3 above that of the enclosing vessel and 



