348 Mixter — Determination of the Heat of Dissociation 



with sufficient acetylene to effect when exploded complete 

 decomposition. The heat found less that due to the acetylene 

 equals the heat of dissociation of the compound. The method 

 is open to the objection that the errors are cumulative. 



The apparatus used in the work is shown in fig. 1. The 

 outer double-walled vessel, J, J, called for convenience the 

 jacket, contains 20 liters of water, which may be stirred before 

 an experiment by the screw propellers. The tin vessel, A, A, 

 separates the calorimeter from the jacket by two air spaces. 

 The calorimeter vessel is tinned iron. The top of it was 

 imperfectly covered by a thin sheet of celluloid and was 

 exposed to the air of the room. The steel bomb B has a 

 capacity of 602 cc , weighs about 1900 grams, and is supported 

 by a bar of wood resting on the top of the calorimeter case. 

 It was silver-plated to prevent rusting and the silver on the 

 interior surface was covered with a thin plating of gold. 

 After the explosions of acetylene the inside plating showed 

 minute perforations with projecting edges, owing doubtless to 

 enclosed particles of plating solution which gave off steam 

 when heated, as electro-plate is known to shut in minute parti- 

 cles of solution which are not removed by washing or drying. 

 The explosions of a mixture of acetylene or ethylene and 

 oxygen dulled the surface of the gold and- gradually removed 

 the metal in the state of fine powder. The explosions of 

 acetylene were noiseless, while those of mixtures of oxygen 

 gave a distinct report, threw the water against the cover and 

 loosened the screws at the top and bottom of the bomb. 

 Ignition was attained by electric sparks between a strip of 

 platinum foil connected with the bomb and a platinum wire, E, 

 insulated by a piece of clay pipe stem projecting into the bomb 

 and a glass tube in the steel tube, D. The foil was commonly 

 melted and the wire, which was l^ mm thick and extended into 

 the bomb several millimeters, was bent by the detonations of 

 acetylene and oxygen. The mean of five accordant calori- 

 metric determinations of the water equivalent of the bomb 

 and calorimeter can was 250 grams. The error is probably too 

 small to affect the results in the fourth figure, since the weight 

 of the apparatus times the specific heat of iron is 262 with no 

 allowance for the small amounts of other metals present. 

 Upon changing a fitting on the bomb the number 252 w T as 

 adopted. A differential thermometer graduated to hundredths 

 of a degree was used. It was found to agree with a normal 

 thermometer and one graduated to tenths. The zero of the 

 differential thermometer was not changed during the work and 

 corresponded to 1 6*4° of the normal. 



In none of the experiments was any measurable quantity of 

 acetylene found in the gas remaining after an explosion and in 



