66 Scientific Proceedings^ Royal Dublin Society. 



is weighed, ai)d filled as before with mercury, the bulb being left open. 

 Let us suppose that at the temperature of tlie room or of cold water (i!° C), 

 the mercury fills the bulb and stem to the point b. The apparatus and 

 mercury are weighed, and the mass of mercury now in the bulb is determined. 

 We sliall refer to this as {M). 



The little flask shown in fig. 1, provided with a two-holed rubber stopper, is 

 now attached to the end of the stem, and is also connected to the small exhaust- 

 pump. The bulb is immersed in a beaker or suitable vessel containing the 

 substance in a liquid state, at a temperature about 10° above its melting- 

 point. 



Tlie open tip of the capillary will lie under the surface of the liquid, by 

 reason of its being at a lower level than the stem. On exhausting, the 

 substance is admitted into the bulb, and the mercury withdrawn and caught 

 in the flask. If any bubbles of gas collect in the bulb, they are quickly 

 removed by forcing back the mercury. When the bulb is about three-, 

 fourths full, the top of the cajiillary is brought outside the liquid and sealed. 

 The pump and flask are detached ; and at this stage or at the end of the 

 experiment, tlie weight of tlie apparatus and its contents of substance and 

 mercury are found, and also tiie weight of mercury expelled and caught in tlie 

 flask. This latter mass will be referred to as {m) ; and the mass of the sub- 

 stance in the bulb, which is easily got from the previous weighings, will be 

 called W. 



Tiie bulb is finally placed in the bath, and the stem adjusted to the 

 millimetre scale as in the preliminary experiment. The bath is iieated and 

 stirred, and the temperature is regulated and changed through the necessary 

 range from about 10° above to 10° below tlie melting-point ; tiie reading 

 [R) of the meniscus is made at the different temperatures. The temperature 

 is altered very slowly, especially during fusion ; the thermometer and the 

 reading R must be found to remain constant for some time before the reading 

 is recorded. The observations are taken first when the substance is cooling, 

 and then when it is being heated througli the same range of temperature. 



The same bulb may be used for several determinations ; and at the end of 

 a test it can be readily emptied and cleaned as follows : — The top of the 

 capillary above the bulb is broken off, and the bulb is immersed in boiling 

 water to which some caustic soda is added. The stem is now attached to a 

 small pump which may be used for exliaust and compression. By alternating 

 the action of the pump, the bulb is soon emptied of wax and filled with the 

 boiling solution, and all greasiness is soon removed. It is well to clean the 

 apparatus finally witli distilled water, ether, and, if necessary, with nitric 

 acid and distilled water. 



