Vapour-Densities of some Carhon Compounds. 501 



approximately from the molecular weight and density of the 

 liquid in question ; after sealing off the point of the stem is 



Fio-. 3. 



I 



melted so as to form a knob about 1 or 2 mms. in diameter. 

 and a nick is made with a glass-cutter in the capillary about 

 1 cm. from the end. (The filled bidb is shown in fig. 3, u.) 

 In the case of methyl alcohol lime was substituted for phos- 

 phoric anhydride. 



TJie Limits of Accuracy* 



The accuracy of the final result depends on the measure- 

 ments of four quantities, namely, the pressure, the volume, 

 the temperature, and the weight of substance introduced 

 into the volume-tube. The smallest pressure that has been 

 measured with this apparatus is 220 mms. The divisions of 

 the scale employed, when corrected by the calibration table 

 pre^dously referred to, are consistent to 0*01 mm. The 

 pressures given in the tables on subsequent pages are the 

 differences between two readings on the scale, each of which 

 is the mean of three independent readings for which the 

 surface of the mercury is re-set to the point under observa- 

 tion. In no case did the eight settings differ by more than 

 0*05 mm., whilst in the great majority of cases they lie 

 within 0"03 mm. ; so that the extreme error due to readinor 

 of pressure may be taken as about 0*05 mm., or about 1 in 

 4000. As will be seen from the curves and tables given 

 later it is only occasionally that a point is found to diverge 

 so widelv from the curve. 



