426 DETERMINATION OF THE FREEZING-POINT DEPRESSIONS 



well stirred, and any change in temperature was quickly recoicled 

 by the thermometer. 



It was so arranged that both these stirrers viz., the one in 

 the protection bath and the one in the freezing-tubes should 

 have the same stroke. Hence they were both fastened to a 

 slider on a vertical guide-post. This slider was worked by a 

 crank vertically above it. The axis carrying the crank was- 

 turned by a hot-air motor. The stroke of the crank was equal 

 to the stroke required by the stirrers. 



The two thermometers viz., the one in the protection bath, 

 and the one in the freezing-tubes were both of the Beckmann 

 form, and were graduated to .01 degree. The one used in the 

 freezing-tubes had been calibrated at the Physikalisch-Technische 

 Reichsanstalt, Berlin. The value of its degree its length being- 

 about 5.4i cm. was given to the third place of decimals. As^ 

 however, it had been tested with its bulb at OC. and its scale 

 at 15C., I had to make a correction due to the fact that I used 

 it with its scale also at OC. In the corrected form the value 

 of the degree was correct. For some time before it was used, 

 and while it wa* being used, it was kept hanging in a vertical 

 position with its bulb and scale approximately at zero. This 

 precaution is indispensible, as the constancy of the thermometer 

 depends on it. This thermometer was read by means of a 

 microscope, which was firmly mounted on an adjustable stand. 

 The eye-piece of the microscope contained a micrometer scale, 

 thirty-seven divisions of which corresponded to .01 degree. As 

 half divisions were easily estimated I could read to .0001 degree. 

 To get a clear imagine of scale and mercury, a small incandescent 

 lamp.driven by a current from several Samson cells, was placed, 

 when a reading was being taken, directly behind the thermometer. 

 As, however, the mercury and scale are at different distances 

 from the microscope, one cannot focus the both at once. Hence 

 I always made a reading with the mercury focussed, for it waa 

 quite easy to estimate the centre of the blurred image of the 

 scale line. In the course of my experiments, I found out how 

 important it was to have the microscope always inclined at the 



