Dixon — A Thermo- Electric Method of Cryoscopy. 53 



k indicates iu the formula the velocity coustaul of the temperature 

 exchange between the freeziug-bath and the solution. It is dependent largely 

 on the form of the apparatus and on the heat-capacity of the solution. 



K is the constant for the velocity witli which the ice and the solution 

 come into equilibrium, viz., it depends on the amount of ice present, its 

 surface, its fineness of division, and tlie energy of the stirring. 



If we were dealing witli two similar watery solutions in the thermo-electric 

 method, it is evident that the convergence temperature depending upon the 

 loss of heat to tlie freezing-bath and the gain by stirring is the same for the 

 two tubes. In the comparative experinaent, however, the actual temperatures, 

 t' of the formula, will of course be different for each, that of tlie water being 

 the higher. Hence the error, represented by t' - t„ will tend to reduce the 

 amount of the observed depression. 



k will be the same for both liquids. 



K will be different for the two. In the solution less ice will separate 

 than in the water for a given temperature of the freezing-bath ; but, at the 

 same time, it is, in practice, found to be more finely divided. These two 

 differences will act in opposite directions. 



The calibration-curve given in fig. 4, which is sensibly a straight line, 

 shows that these eri'ors practically neutralize each other, and that in the 

 working of the method the galvanometer-deflection is proportional to the true 

 depression of freezing-point of the solution examined. 



Bearing in mind the desirability of eliminating all needless junctions 

 from the circuit, one would like to connect the leads coming from the 

 junctions on the pine supports directly with the terminals of the galvano- 

 meter. The importance of reversing the current through the galvanometer 

 owing to shifts in the zero position of the mirror, and the advantages of 

 being able to disconnect the couple readily from the galvanometer during 

 various manipulations, render a key of some form or other necessary in the 

 circuit. Such a break in the continuity of the leads involves a pair of 

 junctions. Experience shows that even when the junctions are between two 

 pieces of the same wire, thermo-electric eifeets are produced if they are not 

 at the same temperature. In order to keep the two junctions as closely us 

 possible at the same temperature, the following arrangement was adopted : — 



The leads coming from the couple are disposed so that their naked 

 ends are exposed on opposite sides of a flat vertical support. It was my 

 practice to stitch each naked end several .times through a piece of thin 

 cardboard in such a manner tliat when the card was bent and folded across 

 the support the stitches made of the two wires lay on opposite sides of the 

 support. 



