700 PROCEEDINGS OF THE AMERICAN ACADEMY. 



uated for complete immersion and in the capillary method most of the 

 stem would be outside the bath, the reading was several degrees too 

 high. For this method, therefore, the standardization of the instrument 

 was based upon a definite depth of bulb immersion, the substance being 

 always level with the bulb. As fixed points there were taken, at sev- 

 eral room temperatures, the boiling point of oxygen (—182.8°), the 

 sublimation point of a thin, homogeneous mixture of carbon dioxide 

 and absolute alcohol (—78.3°), and the melting point of pure mercury 

 (_39°)_58 ^fhe corrections thus determined were well suited for tem- 

 peratures between —100° and —50°, but in the region of —28°, the 

 uncorrected melting point of pyrosulphuryl chloride, the variation for 

 a degree in the stem temperature (determined by a mercury thermom- 

 eter alongside) was considerable. To avoid troublesome corrections at 

 this point, the melting point of pure mercury was taken in the same 

 manner and at the same time as that of the sample. As the melting 

 points of mercury and pyrosulphuryl chloride differ by only two de- 

 grees, the correction could fairly be assumed to be the same for each. 

 In the immersion method, the fixed points were the boiling point of 

 oxygen, the sublimation point of the carbon dioxide-alcohol mixture, 

 and the temperature of melting ice ; corrections being made from a 

 curve plotted from these. 



The bath used was a naphtha, liquid and mobile at —150°, contained 

 in a small beaker, which in turn was immersed in a beaker of liquid 

 air. The inner beaker was covered by a stout filter paper, fastened 

 under the rim in order to prevent the naphtha from becoming opaiiue 

 through condensation of moisture and carbon dioxide. The filter paper 

 was provided with suitable holes for the thermometer, concentric 

 stirrer, etc. 



The liquid to be tested is introduced into the capillary tube by 

 warming and cooling the latter ; sometimes the powdered frozen liquid 

 can be added in the ordinary way. In either of the two methods, ca- 

 pillary or immersion, the tubes are placed in the bath and the liquid in 

 them solidified under stirring of the bath. The liquid air beaker is 

 then lowered and the temperature of the bath allowed to rise as slowly 

 as possible, under careful stirring. This retardation, which may be 

 accomplished by the approximation of the liquid air, is necessary, as 

 otherwise the bath may rise several degrees in one minute and a fusion 

 may take place between too great extremes. The rising thread is al- 

 ways read, and care is taken to see that it is unbroken, a frequent 

 danger in these instruments. 



«>8 Constants from Ostwald-Luther, Hand- und Hiilfsbuch, 1910. 



