RESEARCHES ON THE VOLATILE HYDROCARBONS. 10 



If the bulb be in the vapor, the occurrence of either of these disturbing inn\ienc< 

 would then affect the principal mass of the mercury in the thermometer J while, on 

 the contrary, if the bulb were in the liquid, only the small quantity of mercury in the 



stem of the thermometer would be subjected to these influences; the liquid then 

 serving as a regulator, and reducing the error from these -ourct-a to a minimum 

 Fluctuations from currents of cold air are comparatively slight, and more easily pre- 

 vented than those from overheating the vapor. The latter is the more likely to 

 occur the lower the boiling-point of the liquid, or when the quantity of liquid in tlie 

 retort is small. I have, however, observed from this cause an elevation of 3'-4° in 

 distilling a body boiling as high as 98° C, without an unnecessarily large flame. But 

 the liquid in this instance was pretty low in the retort. 



In the case of liquids boiling below the common temperature, it seems indispensable 

 that the bulb of the thermometer should be placed in the liquid. Afl evidence of this 

 I will here state the results of observations made while occupied in fraction ing some 

 exceedingly volatile products from American petroleum. 



Experiment 1. — The liquid operated upon boiled at so low a temperature that the 

 distillation was effected by the heat of the surrounding atmosphere. The distillation 

 was conducted in a flask, and the bulb of the thermometer placed in the vapor. The 

 flask was attached to my condensing apparatus, including the a refrigerator, B, Fig. 2."* 

 The temperature of the condensing-worm contained in the "elevated bath, aa, Fig. 2,"* 

 and also that of the " first receiver, *. Fig. 2,"* was 11°.5. The temperature of the 



"cold bath, ii, Fig. 2,"* was 11°. The condenser in "the refrigerator, b," and tie 

 "second receiver," were cooled in a mixture of ice and salt. With the liquid boiling 

 steadily from several points on the bottom of the flask, and the condensed product 



stillation running well from the refrigerator into the "second receiver," 



from the d 



not a drop was condensed in any of the apparatus intervening between the flask and 

 the " second receiver," although this part of the apparatus was cooled, as already 

 stated, to about 11°. The temperature of the vapor in the flask at this time was 

 18°.5, or only 2°.5 below the temperature of the laboratory. These observation show 



quid was boiling at a temperature considerably below that indicated by 



thermometer in the vapor. Additional evidence of this was furnished by the fact 

 that, during- the distillation, the exterior of the flask, from the bottom to about one 



th 



quarter of an inch above the surface of the liquid, was thickly covered w 

 condensed from the atmosphere, resembling heavy dew ; while above, the sides of 



American 



