vin THERMO-ELECTRIC CRYOSCOPY 173 



solution and the water stood at a level of 3*3 cm. in 

 similar tubes ; it was reduced to 115*4 mm., when the 

 depth of the salt solution was increased to 5 cm. Of 

 course it is easy to arrange that both tubes should contain 

 the same amount, and so have practically the same heat- 

 capacity. 



Change of resistance of the circuit due to temperature 

 changes is guarded against by completely immersing the 

 eureka or nickel of the couple in the freezing-chamber, 

 while the resistance of the galvanometer is kept constant 

 by its being enclosed in the thermostat. The complete 

 immersion of the connecting-piece of the couple in the 

 freezing-chamber also secures the elimination of thermo- 

 electric effects due to want of uniformity in this wire. 



From what has been said, it will appear that the thermo- 

 electric method is capable of considerable accuracy, even 

 when only two junctions are employed. Of course if it 

 were desired to work to greater accuracy, there would be 

 no reason why the number of junctions should not be 

 increased, thus greatly increasing the galvanometer deflec- 

 tion for the same temperature interval. In the work in 

 which we were engaged, however, this would have been 

 undesirable, as a comparatively large range was required. 



But even with a pair of junctions, the hundredth of a 

 degree could be measured with certainty. With this 

 accuracy very small quantities of fluid may be dealt with. 

 The small quantities required render the method particu- 

 larly suitable to physiological work. Its differential charac- 

 ter might also be applied with advantage to comparing the 

 freezing-points of different fluids ; for example, in a com- 

 parison of jugular and carotid blood. 



Literature. 



Dixon, II. H., ' Observations on the Temperature of the Subterranean 

 Organs of Plants," Trans. Boy. Irish. Acad. 1903, vol. 32 B, p. 145. 



Id. "A Thermo-electric Method of Cryoscopy,'' Proc. Boy. Dublin Soc. 



