22 Conductivities and Viscosities in Pure and in Mixed Solvents. 



the distillation flask, passed through a soda-lime tower (not shown in 

 the drawing, but appears on the left in plate 1 ; then through the two 

 wash bottles (fig. 5, A), and finally over phosphorus pentoxide con- 

 tained in the long tube B, which was protected by two glass stopcocks, 

 the one sealed permanently into the tube and the other securely fast- 

 ened with sealing-wax in the left-hand tapered end of B. This joint 

 made it possible to open B in renewing the phosphorus pentoxide. 

 From B, the current of air passed into c, through a short rubber 

 connection and a right-angle glass bend, the open end of which is 

 connected with c by a rubber joint made air-tight with rubber cement. 



The distillation head c consisted of a short projecting tube, a well- 

 ground stopcock of large bore; the ground connection with the 750 

 c.c. distilling flask D, and the long inner tube reaching to the bottom of 

 the flask and drawn to a capillary at the end, so as to cause the air to 

 bubble in a fine stream through the liquid. Connection between the 

 flask and the condenser was effected by a ground joint designed to 

 prevent the liquid distilling over from coming in contact with the stop- 

 cock grease used in making the joint air-tight. The condenser was also 

 ground into the Axtell receiver F, which is too well known to require 

 further description, other than to state that the capacity of the barrel 

 was about 100 c.c. and that of the small bulb 250 c.c. The receiver 

 allowed the removal of different fractions without interrupting the 

 vacuum. 



The receiver was connected with the pump K, through the gas wash 

 bottles A', the soda-lime tower i, and the three-way stopcock j. One 

 of the wash bottles was filled just to the upper level of the holes in 

 the inner cylinder with sulphuric acid ; the other was empty, serving 

 as a trap in the case of back-pressure. The construction of the wash 

 bottles secured a maximum exposure of acid to the possible alkaline 

 vapors (NHs) without appreciable back-pressure. 



Liquid f ormamid was introduced into the flask at any time during the 

 distillation without destroying the vacuum, by closing the stopcock on 

 c, temporarily disconnecting the air inlet, and attaching at the same 

 point the flask and siphon N. On opening the stopcock the diminished 

 pressure in the flask drew in any liquid in N. 



During the distillation the flask was immersed in a bath of hardened 

 cottonseed oil ("Crisco") , into which the thermometer dipped. Ordinary 

 rectified cottonseed oil was first used, but this was soon discontinued, 

 since the oil quickly became rancid and offensive when heated. The 

 "Crisco," however, remains sweet and untainted even after continued 

 use. The temperature in the outer bath was maintained at from 

 10 to 15 higher than the boiling-point of the liquid at a given pressure, 

 the usual temperature being 100 to 1 15. In the apparatus used in the 

 preliminary work a thermometer was sealed into the air-inlet tube of 

 c, with its bulb well down in the flask, and the boiling-point of the 



