Dixon — A Thermo- Electric Method of Cryoscopij. 57 



quarter filled with salt solution, and then finely divided ice is added till the 

 vessel is filled up to within about 3 em. of the brim. A stout brass wire 

 stirrer of the usual form is used to mix the brine and ice. Salt is added till 

 the desired temperature is attained. This should be about X'^f 0. below the 

 freezing-point of the solution to be examined. If the proportion of ice to the 

 liquid is large, this temperature may be maintained constant by occasionally 

 adding a little salt. A brass lid is fitted to the freezing-vessel, and supports 

 the large test-tube which forms the freezing-chamber. It is also perforated 

 to admit a thermometer into the freezing-bath and to allow the stii'rer in the 

 bath to project from it. 



To make an observation with the apparatus — say, to determine the 

 freezing-point of a solution — the procedure is as follows : the leads of the 

 thermo-couple are slipped through the slit and the pine supports through the 

 holes in the upper cork bung, and the stop is fixed on one of the supports 

 above the cork, to prevent them falling down. The freezing-chamber is 

 then closed with the cork. Meanwhile two small test-tubes, one containing 

 about 2 c.c. of the solution, and the other the same quantity of distilled 

 water, are being cooled by supporting them in the freezing-bath, making 

 use of the perforation in the lid through which the stirrer works. 



When it is judged that they have reached their freezing-point, a little 

 hoar-frost is detached on a cooled platinum needle from the outside of the 

 freezing- chamber and introduced into the distilled water. Ice crystals are 

 immediately formed, and some adhere to the needle, which is then transferred 

 to the salt solution. Crystallization is instantaneously started in this and 

 the needle is withdrawn. The two test-tubes are now put into the holes of 

 the smaller cork, and it is fixed on to the lower end of the wire handle which 

 passes down through the upper cork, and whicli has been removed from the 

 freezing-chamber momentarily for the purpose. The junctions on the lower 

 ends of the pine supports are now immersed in the freezing-liquids in the 

 test-tubes. Thus arranged the whole, test-tubes and thermo-couple, is put 

 into the freezing-chamber and the upper cork tightly adjusted. Stirring 

 of the freezing-fluids is immediately commenced by moving the pine rods up 

 and down. As these are rigidly connected together, the two test-tubes are 

 subjected to precisely similar conditions in this respect. The freezing-bath 

 is also kept stirred. The galvanometer may now be put in circuit with the 

 thermo-couple by fixing the clip on the support in the petroleum key ; and 

 the petroleum is occasionally stirred. Immediately on making the contact 

 the spot of light travels from zero. At first its motion is rapid, but becomes 

 slower and slower till at last it moves with an almost imperceptible creep. 

 It comes to rest about 60 sees, after contact is made. It will be found 



SCIENT. PBGC. K.D.S., VOL. XIII., NO. IV. 5 



