282 Wadsworth — Determination of Specific Heat, etc. 



4. 



JSTotes on the Bunsen Ice Calorimeter. 



Filling. — More or less elaborate directions are generally 

 given for filling the body of the calorimeter with water and 

 mercury. The following process, which I have used for some 

 time, is very simple, direct and efficient. The required quan- 

 tity of mercury is first poured into the calorimeter through a 

 small glass funnel, whose stem has been drawn out into a long, 

 fine bulb, which will reach to the bottom of the side tube b, of 

 the calorimeter. The calorimeter is then 

 inverted in a beaker of distilled water deep 

 enough to cover it to above the bend of 

 the side tube, as in fig. 4. The mercury 

 already introduced, which is now in the 

 upper part of the water chamber, will hold 

 the calorimeter down under the water. 

 The beaker containing the water is now 

 heated to boiling and cooled. When the 

 calorimeter chamber a has been partly 

 filled with water by the cooling, the whole 

 is raised to boiling again, and kept at that 

 temperature until all the air in a has been 

 replaced by steam. On cooling again a 

 will be completely filled with hot, air free, 

 water. When cool enough to handle, the 

 finger is placed over the mouth of b and 

 the calorimeter removed from the water and turned into the 

 upright position. The mercury will run down to the bottom 

 of a, leaving, however, some water still in b. This is then dis- 

 placed by more mercury introduced through a funnel as before. 

 Maintaining at Zero Temperature. — In using the ice calori- 

 meter it is necessary, as has been pointed out by Bunsen, to 

 have the calorimeter surrounded by pure melting ice or snow 

 of exactly zero temperature. Since perfectly pure ice or snow 

 is difficult to obtain, it occurred to the writer some time ago 

 that the most convenient way of securing the desired result 

 would be to immerse the calorimeter in a vessel (a wide- 

 mouthed bottle has proved very convenient in practice) filled 

 with distilled water, and freeze a shell of pure ice on the 

 inside of this bottle by placing it in a freezing mixture, leav- 

 ing a space between ice and calorimeter filled with pure dis- 

 tilled water. When this has been done the whole arrangement 

 is then placed in a larger vessel filled with ordinary crushed 

 ice or snow. If this is not exactly at zero temperature (owing 

 to impurities) the only result will be to cause a slow progres- 

 sive freezing or thawing in the ice shell of the inner vessel. 

 The distilled water being in contact with pure ice will, if occa- 

 sionally stirred, remain at zero temperature. 

 Yerkes Observatory, June, 1897. 



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