66 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Ethyl Chloride. — Two sets of measurements were made on this 

 substance, separated by thirty-six days in time, both with the smaller 

 bulb, and both complete for compressibility and dilatation over 

 the entire pressure range. Both runs were entirely without accident 

 of any kind. The very low boiling point of this substance, 12.5", and 



0123456789 10 11 12 

 Pressure, kgm. / cm.^ x 10^ 

 Phosphorus Trichloride 



Figure 16. Phosphorus Trichloride. Volume at 20°, 40°, 60°, and 80° 

 plotted against pressure. The lower curve is for 20°. 



its abnormally high compressibility, made slight changes necessary 

 in the details of the manipulation. The ethyl chloride was furnished 

 by Kahlbaum, in sealed glass bulbs, which were accordingly exposed 

 to an internal pressure greater than atmospheric. The steel compressi- 

 bility bulb was filled after the ethyl chloride and the bulb had been 

 brought to 0° in an ice bath. The steel bulb was then allowed to warm 

 sufficiently to boil away a slight quantity of the ethyl chloride, when 

 the capillary stem of the bulb was closed by forcing into it a small 

 rubber stopper, considerably too large for it. The friction of the 

 stopper was sufficient to hold it in place against the vapor pressure 

 of the ethyl chloride at room temperature. The first application of a 

 very moderate pressure by the pump was sufficient to drive the stopper 

 into the bulb, where it remained during the rest of the measurements. 

 In this way the filling could be accomplished without the troublesome 

 necessity of cooling the large cylinder below 12° and maintaining it 

 there until pressure could be applied. The small rubber stopper was 



