Expansion of Salt- Solutions. 389 



diameter ; the shorter tube is closed and rounded at the lower 

 end. A brass cap, firmly cemented on to the wide end of the 

 outer tube, carries the side tube bent at right angles, by which 

 communication is made with the Y-shaped condenser. The 

 inner tube is secured air-tight in the cap by an indiarubber 

 cork, the lower end being kept in the centre of the outer tube 

 by a ring with three projecting arms. The free upper end 

 of the Y-condenser communicates with the pressure-regulator, 

 a WoulfFs bottle being interposed to retain any liquid boil- 

 ing over. The lower end of the Y passes to the bottom of the 

 boiler, which is a stout copper cylinder 150 millim. high and 

 120 millim. in diameter, and stands on a solid flame-burner. 



When the boiler has been one third filled with alcohol, the 

 whole apparatus is made as nearly air-tight as possible, and 

 connected with the pressure-regulator. The inner tube is 

 filled with water, the gas is lighted, and the pressure is re- 

 duced the desired amount. The vapour of the boiling alcohol 

 passes up between the two tubes, entirely surrounding the 

 inner for its whole length. At first the condensed alcohol 

 flows back into the boiler; but as the temperature of the water 

 in the inner tube rises, the alcohol vapour passes into the 

 condenser and thus back to the boiler, complete condensation 

 being insured by the second limb of the Y-tube. 



The pressure-regulator is shown at fig. 4 : it is based partly 

 on that proposed by Meyer, and partly on the modification 

 introduced by Stadel and Schummann *. It consists of a 

 firm wooden stand some 900 millim. high by 200 millim. 

 wide. A gauge, standing side by side with a barometer in a 

 trough of mercury in front of a mirror-millimetre scale, is 

 connected with a tube passing across the stand near the top, 

 and bent down as shown on one side, ending in a wide closed 

 cylinder. The tube is furnished with two stopcocks, the upper 

 to establish communication with the air when desired, the 

 other communicating with the bath. On the other side of the 

 gauge there is a T-piece, the vertical limb of which passes 

 through the stand, while the horizontal limb leads to the 

 " cut-off.''' This arrangement is shown on a larger scale at 

 the side A. It consists of a narrow tube some 300 millim. 

 long, opening at the top into the wide tube furnished with a 

 narrow side tube. Into the upper end of the wide tube is 

 fastened air-tight another tube, only slightly narrower ; it is 

 contracted at the lower end to a small orifice, and a small 

 hole is made at the shoulder. (The delicacy of the regulation 

 depends to a large extent upon the proper size and position 

 of this opening.) To the upper end of this tube, which is 



* Zeitschrift fiir Instrumentenkunde, 1882, p. 391. 



