Saline Solutions at High Temperatures. 85 



bubble at various temperatui'es, I fixed a lens, having a focal 

 length of 5 inches, as an object-glass to a microscope, and pulled 

 out the tube of the microscope until the distance of the eye-piece 

 was such that each division of the micrometer in the eye-piece 

 corresponded to -^ho^^ ^^ ^" inch. In this manner the length 

 of the bubble in the tube could be easily measured to within 

 TUUo*^ of an inch. Of course when the liquid in the tube ex- 

 panded the length of the bubble diminished to the same extent, 

 and thus a knowledge of the length of the bubble at various 

 temperatures was sufficient to enable me to ascertain the amount 

 of the expansion of the liquid to within about gjjij^th of its 

 volume. This may indeed be thought not at all an accurate 

 determination; but in making the experiments at a high tem- 

 perature, there are several sources of error which have such a 

 great influence, that to attempt an apparently greater accuracy 

 would not really give a better result. 



In order to heat the tube to various high temperatures, I fixed 

 it in a glass beaker containing melted paraffine, which, on ac- 

 count of remaining so liquid and transparent, is a substance ex- 

 tremely suitable for such experiments. I so arranged the whole 

 apparatus that the bubble in the tube was in the focus of the 

 microscope, which was placed horizontally, so that the length of 

 the bubble could be accurately measured whilst the liquid in the 

 tube was at the temperature shown by a thermometer passing 

 into the paraffine through a hole in a piece of card-board cover- 

 ing the beaker. In making the experiments at high tempera- 

 tures, I found it very difficult to maintain the paraffine at nearly 

 the same heat for so long a time that there was no doubt that 

 the liquid in the tube would have the temperature shown by the 

 thermometer. By carefully managing the gas-lamp, this could 

 be accomplished moderately well ; but it was so difficult that I 

 found it best to cause the heat to increase very slowly, and, when 

 at the coiTcct temperature, to quickly measure the length of the 

 bubble. I then caused the heat to diminish gradually, and again 

 measured the length when at the correct temperature ; and, if 

 all this was carefully performed, the length of the bubble was 

 nearly the same, whether the temperature was increasing or de- 

 creasing, and therefore the mean of the two could not be far 

 from the truth. Still, with every care, the various measure- 

 ments difl'ered very notably, perhaps on account of its being im- 

 possible to make the whole of the bath of paraffine of precisely 

 the same temperature, and therefore I made a considerable num- 

 ber of measurements, and adopted the mean of all for the true 

 determination. 



Having then ascertained the length of the column ol' liquiil 

 in the tube at a given temperature, aud likewise measured the 



