282 



Scientific Prnccedings^ Boijal Dublin Snciehj. 



correspouded to the temperature of melting ice. Wlien the two couples 

 were at the same temperature, i.e., were close together in a vessel of water 

 vigorously stirred, tlie cross-line on the spot of light stood at 250 mm. on 

 the galvanometer scale, its middle point. 



Calibration. 



By suhtractioij we get — 



(1) 112-5 mm. - 607 mm. = 51-8 mm. = 1-069° - 0-569° = 0-500° 



.-. 1 mm. = 0-00965° 0. 



(2) 283-6 mm. - 60-7 mm. = 172-9 mm. = 2-235° - 0-569° = 1-666° 



.-. 1 mm. = 0-00964° C. 



(3) 233-6 mm. - H2-5 mm. = 121-1 mm. = 223-5° - 1-069° = 1-166° 



.-. 1mm. = 0-00920° C. 



No. 3 gives a larger deflection per 0-01° C, inasmuch as for the greater 

 deflections the spot of light is approaching the limit of the scale. This 

 calibration agrees well with the calibrations by a different method given 

 later on. 



Subsequently, when it was found desirable to surround the couple 

 completely in the cooling-bath, the calibration was made by having distilled 

 water in one of the test-tubes in the apparatus already described, and a 

 solution of sugar having a known concentration in the other. 



From Eaoult's results the freezing-points of sugar solutions of various 

 concentrations are known with great accuracy ; and consequently the value 

 in degrees centigrade could be assigned to the deflection registered by the 

 depression of freezing-point for any solution. 



In flg. 2 the line R shows Raoult's results^ for the depression of the 

 freezing-point corresponding to different concentrations, the abscissae being 

 the temperatures and the ordinates tlie number of grams of sugar per 



1 Eaoult's results are quoted from If. J. Hainbiiraer. Osmotisclier ijruclc und lonenlelirc 



