16 



1st, Whether the melting point of different specimens 



of paraffin is the same. 

 2nd, Whether that of the same specimen remains the 

 same. 



The method of observation adopted in these experiments 

 was as follows. The thermometer had its stem fitted into 

 the cork of a colourless glass flask so that when the flask 

 was corked the bulb was in the centre of the flask, the ex- 

 tremity of the mercurial column appearing during the 

 experiment slightly above the cork. The flask was kept 

 heated to a point slightly below that of the melting point 

 of paraffin. The bulb of the thermometer was then dipped 

 for a few seconds into some melted paraffin a few degrees 

 above its melting point, and while covered with a fluid 

 coating of paraffin was replaced in the centre of the flask. 

 The flask being only a very little colder than the bulb, the 

 cooling was then very slow. 



The instrument was placed so that the reflected image of 

 the bar of a window was seen distinctly in the mercury of 

 the bulb through the liquid paraffin. One observer carefully 

 scrutinised this reflected image by a lens, while another 

 watched the downward progress of the column of mercury in 

 the stem of the thermometer. As soon as the observer scru- 

 tinising the image observed a want of definition produced by 

 incipient freezing, he noted the circumstance to his col- 

 league watching the column, and thus the exact reading at 

 which freezing began was ascertained. It was found easily 

 possible to ascertain this point to one tenth of a degree 

 Centigi^ade. Four or five separate observations were gene- 

 rally taken, before each of whicli the thermometer was 

 re -dipped into the melted paraffin. 



In case of any change taking place in the zero of the 

 thermometer while the experiments were in progress, the 

 instrument was tried in melting ice before each experiment. 



