476 



Mr. H. M. Vernon on 



a large vessel of water kept at a constant temperature through- 

 out the experiment. On the dioxide was poured a volume of 

 concentrated hydrochloric acid, varying from 5 to 10 cub. 

 centim. in different experiments. The temperature of the 

 bath was varied in different experiments from 31° # 5 to 75°. 

 Above this temperature the rate of evolution becomes so rapid 

 that it is impossible to measure the volume of gas evolved 

 accurately. The air evolved was collected over water. The 

 volume of the apparatus was very much larger than that 

 of the chlorine evolved ; and it was found experimentally that 

 scarcely a trace of chlorine reached the collecting-tube even 

 after several hours. Observations were made at intervals of a 

 quarter or half a minute, or at greater intervals when at the 

 close of an experiment the evolution became much slower. 

 The results obtained are represented diagrammatically in the 

 illustration. Here the ordinates represent the volume of gas 

 evolved in cub. centim., and the abscissae represent the time 

 in minutes. The first curve represents the rate of evolution 

 at 75° C. It will be seen that the gas is evolved very rapidly, 

 more than half of it coming off in the first minute, while all of 

 it appeared to have come off in half an hour. 



3 40 



is 30 













































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10 



50 60 



Time, in minutes. 



70 



80 



90 



100 



The second curve gives the rate of evolution at 50 o, 8. Here 

 the gas is not evolved so rapidly ; even after two hours the 

 evolution did not appear to have quite stopped. The next 

 curve gives the rate of evolution at 31°*5. For this curve 

 each division of the paper represents forty minutes instead of 

 ten minutes. It will be noticed how very much more slowly 

 the gas is coming off here than it did before. Thus it had 



