1897.] on Properties of Liquid Oxygen. 559 



susceptibility of which is to be determined. A second method con- 

 sists in determining the mechanical force acting on a known mass 

 of the liquid when placed in a non-uniform magnetic field. Owing 

 to the difficulty of preventing entirely the evaporation of liquid 

 oxygen, even when contained in a good vacuum vessel, and the im- 

 possibility of sealing it up in a bulb or tube, and having regard to the 

 effect of the low temperature of the liquid in deforming by contrac- 

 tion and altering the conducting power of coils of wire placed in it, it 

 was necessary to devise some method which should be independent of 

 the exact constancy in mass of the liquid gas operated upon, and in- 

 dependent also of slight changes in the form of any coils of wire 

 which might be used in it. After many unsuccessful preliminary 

 experiments the method which was finally adopted by Professor 

 Fleming and myself as best complying with the conditions introduced 

 by the peculiar nature of the substance operated upon is as fol- 

 lows : — 



A small closed circuit transformer was constructed, the core of 

 which could be made to consist either of liquid oxygen or else imme- 

 diately changed to gaseous oxygen, having practically the same tem- 

 perature. This transformer consisted of two coils, the ^primary coil 

 was made of forty-seven turns of No, 12 S.W.G. wire ; this wire was 

 wound into a spiral having a rectangular shape, the rectangular 

 turns having a length of 8 cm. and a width of 1 • 8 cm. This rect- 

 angular-sectioned spiral, consisting of one layer of wire of forty-seven 

 turns, was bent round a thin brass tube, 8 cm. long and 2J cm. in 

 diameter, so that it formed a closed circular solenoid of one layer of 

 wire. The wire was formed of high conductivity copper, doubly in- 

 sulated with cotton, and each single turn or winding having a rect- 

 angular form. 



The turns of covered wire closely touched each other on the inner 

 circumference of the toroid, but on the external circumference were 

 a little separated, thus forming apertures by which liquid could enter 

 or leave the annular inner core. 



The nature of this transformer is shown in Fig. 1. 



The mean perimeter of this rectangular-sectioned endless solenoid 

 was 13J cm. and the solenoid had, therefore, very nearly 3*5 turns 

 per cm. of mean perimeter. When immersed in liquid oxygen a coil 

 of this kind will carry a current of 50 amperes. When a current of 

 A amperes is sent through this coil the mean magnetising force in 

 the axis of this solenoid is, therefore, represented by 4*376 times the 

 current through the wire, hence it is clear that it is possible to produce 

 in the interior of this solenoid a mean magnetising force of over 

 200 C.G.S. units. This primary coil had then wound over it, in two 

 sections, about 400 or 500 turns of No. 26 silk-covered copper wire to 

 form a secondary coil. The primary and secondary coils were sepa- 

 rated by layers of silk ribbon. The exact number of turns was not 

 counted, and, as will be seen from what follows, it was not necessary 

 to know the number. The coil so constructed constituted a small 



