THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. I. — The Lecture Exjyerimeiit with Ligicid Carhon 

 Dioxide ; by C. Barus. 



The well-known glass tubes containing liquid carbon dioxide 

 are present in almost every laboratory ; but the full experiment 

 showing the passage of the liquid through the critical tem- 

 perature is none the less difficult to perform satisfactorily to a 

 class. This implies that the experiment should be made safely 

 and that the progress of the whole phenomenon should be 

 clearly exhibited in a reasonable time. I will, therefore, ven- 

 ture to describe the following method, which has given good 

 results and has thrown light on certain moot questions aside 

 from its immediate purpose. 



The experiment should be made with sunlight, for this 

 facilitates manipulation (the room need not be darkened), en- 

 ables the student to follow the work throughout and simplifies 

 the optic principles involved. Care should be taken to choose 

 a tube not quite filled with liquid, even at the critical 

 temperature ; otherwise the meniscus is lost too soon near the 

 end of the tube. When submerged in a water bath, the 

 effective difference of refraction between liquid and gas is 

 relatively slight and only an imperfect and dark image of the 

 tube and the meniscus is obtained on projection. Most of the 

 light is apparently totally reflected away from the screen. As 

 a special experiment one may even show a tube partially filled 

 with water, side by side with the carbon dioxide tube, the 

 former on projection exhibiting a remarkably sharper contrast 

 between liquid and gas than the latter. 



Hence the phenomenon is to be shown by heating the tube 

 in an air bath. In this case the projected image of the whole 



Ail. JouE. Sci.— FouETH Series, Yol. II, No 1.— July, 1896. 



1 



