BixoN — A Thermo- Electric Method of Oryoscopy. 61 



points of the solutions and that of water. The dotted line is a similar graph 

 of Raoult's freezing-point determinations. Tlie concentrations are plotted 

 against tlie depressions of the freezing-point. In the second graph the 

 abscissae correspond to hundredths of a degree centigrade. 



The couple on which these observations were made had a length of 

 126 cms. interposed between the junctions, as it was desired that it should 

 give about 1 mm. deflection for a temperature difference of 0'01°C. The 

 actual deflection was found to be 110'9 mm. for 1'00°C. 



For some time after being made, tlie thermo-couple used in these 

 observations changed its constant considerably, owing probablj' to some 

 progressive change in the metals of the junction and circuit. After nine 

 mouths, wlien the eoustaut was re-determined, it gave a deflection of 

 130'4 mm. per 1° 0. It liad then become nearly stable, and observations 

 during the next three months showed that its deflection varied between 

 129"2 mm. and 133'0 mm. per degree. The smaller fluctuations are possibly 

 due to clianges in the resistance of the circuit connected with changes of 

 temperature. They show the need of re-determining the constant of the 

 couple during eacli series of observations, just as the zero change of the 

 Beekman thermometer necessitates a control-experiment in the thermometric 

 method. 



With regard to the temperature of the freezing-bath, it would at first sight 

 appear of little importance in this differential method, as, no matter what its 

 temperature is, it will tend to produce the same ' convergence temperature' in 

 each test-tube. It has, however, been found to have an appreciable effect on 

 the magnitude of the deflection corresponding to the freezing-point of a given 

 solution, as will be seen from the table below, in which are recorded the 

 deflections corresponding to tlie freezing-point of a solution of 1"5 gm. NaCl in 

 100 gm. of water, having a freezing-point of 0'886°, when surrounded with a 

 freezing-bath of different temperatures. 



From these figures it appears that when the freezing-bath is less than 

 1'2° below the freezing-point of the solution under examination, a small 

 alteration in the temperature produces a greater effect on the deflection 

 than when the bath is about 1-5° below the solution. It consequently 

 seemed best to adjust the freeziug-bath about 1'5° below the suspected 

 temperature of the freezing-point. 



