164 RESEARCHES ON THE VOLATILE HYDROCARBONS. 



flask were perfectly dry. It was these observations which first directed my attention 

 to the fact that the temperature of the vapor could not in all cases be depended upon 

 for the true boiling-point of a liquid, and naturally led me to make other experiments 

 with special reference to this question. 



Experiment 2. — The conditions of this experiment were somewhat different from 

 those of the first. The liquid operated upon was the extremely volatile product col- 

 lected in the u second receiver" of Experiment 1. The flask employed was smaller, 

 and provided with two thermometers ; the bulb of one of these was placed in the 

 liquid, and that of the other in the vapor. The flask stood in a water-bath containing 

 ice-water ; this bath was also provided with a thermometer. The temperature of the 

 ice-water bath was very gradually raised by means of a small flame from a Bunsen's 

 burner. Temperature of the laboratory, 20° C. Observations during the distilla- 

 tion : 



Temperature of the water-bath, ... . 10 

 1. -J " " boiling liquid, ... 8 



U 



" vapor, . 18°.5 



Temperature of the water-bath, . . . .12 

 2. { " « boiling liquid, ... 9 



" u vapor, 



18 



Temperature of the water-bath, . . . 18 

 15 minutes later. 3. { " " boiling liquid, . . .10 



" " vapor, . . . . 14' 



Temperature of the water-bath, . . . .20' 

 10 minutes later. 4. \ " " boiling liquid, . . . 12 



" " vapor, 



19 



Temperature of the water-bath, ... 23 

 20 minutes later. 5. I " a boiling liquid, . . .15 



" " vapor, 



19° 



Experiment 3. — The subject of this experiment was a liquid which I had separated 

 from the most volatile product of the re-distillation, on a manufacturing scale, of the 

 crude benzole obtained in the distillation of coal-tar. The apparatus employed was 

 essentially the same as that used in Experiment 1, with the addition of the extra 

 thermometers, as in Experiment 2. The eondensing-worm in the "elevated bath, 

 and that in the " cold bath," and also the * first receiver," were all cooled in pounded 

 ice. The condenser in the " refrigerator," and also the * second receiver," were both 



