450 APPENDIX. 



inch in diameter. Take a 30-inch piece of glass tubing that will 

 slide easily within the tin tubes. Bend it at right angles, 12 inches 

 from each end, like the tube shown in Fig. 240. Color a little 

 alcohol with red aniline, and pour into the bent tube enough to fill 

 an inch or two above each bend. Over each arm of the bent tube 

 pass an inch of snugly-fitting rubber-tubing, and slide it down 

 about 8 inches. Pass the arms of the glass tube up through the 

 tin tubes of the inverted cans as far as they will go. Slide the 

 rubber-tubing upward to make air-tight joints between the glass 

 and the tin tubes. Place the cans upon the horizontal strips of the 

 frame already made, allowing the glass tube to hang between the 

 boards. The level of the liquid in either arm may be marked by a 

 thread or rubber band that may be moved up or down. 



