NEW RESEARCHES ON LIQUID AIR. 



143 



of 60 atmospheres in about three minutes. Generally, in the experi- 

 ments, about £ to 4 cubic feet of air passes through the different sized 

 needle holes per minute when the pressure is about 200 atmospheres. 

 As the small hole is apt to get stopped, for general working it is better 

 to use a needle stopcock, worked from the outside by a screw passing- 

 through the middle of the coil of pipe. 



In testing the individual coils as to the amount of air passed per 

 minute under different pressures, the arrangement of apparatus shown 

 in Plate VI was used. 



A is a bottle of compressed air, to which the copper pipe 13 is 

 attached. This coiled pipe first passes through the vessel C, containing 

 water, in order to equalize the temperature, and then through the cork 

 D into the glass vacuum vessel E, when it is led by a large number of 

 convolutions to the bottom, terminating in a minute pin-hole valve F. 

 The released air passes from F right up through the coils and out of 

 the vent by the copper tube G, which in its turn passes through a vessel 

 H, similar in its object to C, and is then conducted to a measuring 

 meter J. 



The following table gives the results of a series of experiments made 

 on one coil as to the rate of discharge of air at different pressures : 



Pressure in 

 atmospheres. 



Cubic feet per 

 minute meas- 

 ured under 

 atmosphere 

 at -15°. 



55 

 105 

 155 



98 

 210 

 •250 

 287 

 290 



0. 22 

 0.42 

 0.63 

 0.79 

 0.84 

 1.00 

 1.15 

 1.18 



The results show that the rate of air discharge through a fine aperture 

 is directly proportionate to the pressure, or the A r elocity with which 

 the gas on the high- pressure side enters the orifice, is independent of 

 the density. Actual measurements of the size of the needle hole 

 resulted in proving that the real velocity of the air entering the aperture 

 on the high-pressure side was about 500 feet per second. In all these 

 experiments the temperature of the coil was not allowed to get so low 

 as to produce any visible trace of condensation in the air jet. Just 

 before liquefaction the rate of discharge of air through the same aper- 

 ture may be doubled, the pressure remaining steady, owing to change 

 in the viscosity of the gas and other actions taking place at low 

 temperatures. The above measurements can only be regarded as rep- 

 resenting the general working of such regenerating coils. 



A double coil of pipe has advantages in the conduct of some experi- 



