and Gases near their Critical Temperatures, 147 



Two methods of heating will be noticed in this paper. The 

 first consists merely in heating a large test-tube of oil over a 

 rose gas-burner, the experimental tube being suspended verti- 

 cally in its axis a little above the bottom by a fine platinum 

 wire. Numerous experiments have been tried with U-tubes 

 of which the branches were of equal diameter aud glass-thickness; 

 and the results show that the heating, although rapid, is nearly, 

 if not quite, uniform. It is worth notice, however, that at 

 temperatures very near the critical, the density of liquid and 

 vapour are so nearly equal that when the heating is made un- 

 equal, the entire disappearance of the liquid from one branch 

 of the tube does not affect its level in the other. The second 

 method of heating is more complex, but has answered the pur- 

 pose sufficiently well to deserve brief description. In the 

 middle of a four-litre beaker of oil* is fixed a round-bottomed 

 thin flask of 1*5 litre capacity. The neck, which is about 

 3 centims. in diameter, is thickly wrapped round with cotton 

 wool and calico, and is long enough to rise 7 centims. above 

 the perforated cover which closes the beaker. The beaker 

 rests on wire gauze carried by a large iron ring, and is sur- 

 rounded by a tin cylinder 8 centims. wider than the beaker, 

 furnished with two small glass windows on opposite sides. 

 The neck of the flask passes through the cover of this outer 

 case, and is closed air-tight by an indiarubber cork, through 

 which the bulb of a long-stemmed thermometer is inserted. 

 Just below the cork is fused into the neck a narrow glass tube 

 connected with a slightly modified Bunsen regulator (fig. 1, 

 Plate III.) by a short piece of composition pipe (a) 2 miliims. 

 in diameter |. The other end communicates through a short 

 glass tube (b) with the air-mercury bulb of the usual regu- 

 lator. A small glass stop-cock (c) serves to place the flask 

 and regulator-bulb in communication with the air. A large 

 rose burner protected from air-currents heats the beaker of 

 oil. 



When the apparatus is in use the experimental tube is 

 suspended in the middle of the flask by a thin wire, the glass 

 stop-cock (c) of the regulator opened, and a small gas-flame lit 

 beneath the beaker. When ether is used in the experiment, 

 in from eight to ten hours the temperature rises to within 



* The best salad oil heated out of contact with such metals as copper and 

 iron will bear repeated heating- to 200° C. It ultimately becomes thicker and 

 denser, and exhibits a green fluorescence. By long exposure to the action 

 of air and light, particularly in thin sheets, it regains its transparency and 

 again becomes fit for use. It should be noticed that some sorts of glass 

 are violently attacked by hot oil. 



f These regulators may be obtained from Mr. Bel, 34 Maiden Lane, 

 Strand. 



M2 



