56 HEAT OR CALORIC. 



letting it pass along the tube, from end to end, measuring it, at short 

 intervals, with a scale or dividers.* 



(b.) Although the tube should not be quite uniform, it may be stilt 

 used.\ 



(c.) To blow the ball, the instruments wanted are the bloiv pipe, 

 and an elastic gum bottle which is useful, perhaps necessary, where 

 the thermometer must be exact that is free from air and moisture. 

 We need also pliers and some bladed instrument. The glass is 

 melted, drawn in two, and thus hermetrically sealed at one end, 

 while it is opened at the other by cracking it, after marking it with a 

 file ; the end on which the ball is to be, is then rounded, by alter- 

 nately holding it in the flame and pressing the hot glass against the 

 blade, to accumulate as much as is needed. The bulb is next 

 blown by the mouth or the elastic bottle, and this part of the opera- 

 tion requires a kind of skill which can be acquired by practice alone, 



(d.) To Jill the ball with mercury. 



First heat the mercury in a ladle, to drive off moisture and air ; 

 filter it by making it pass through pin holes in a paper depressed into 

 a wine glass, in the form of a funnel ; next hold the ball over a spirit 

 or an Argand's lamp, the open end of the tube being immersed in the 

 mercury, turning the ball to prevent fusion or collapse, and holding it 

 in the heat as long as the air continues to issue freely ; then withdraw 

 it and the, atmosphere will raise a column of mercury that will fill 

 the ball, one third or one half. Now bring the ball again over the 

 lamp, with the mercury exposed to the heat until it boils, when the 

 metallic vapor will expel most of the remaining air ; on withdrawing 

 it from the heat, the mercurial vapor will be condensed, and the tube 

 having its open end still immersed in the mercury, the latter will rush 

 in, and nearly or quite fill the ball. 



(e.) To boil the mercury, for the purpose of expelling the remain- 

 der of the air. 



Tie a small paper funnel to the open end of the glass tube, hav- 

 ing joined its edges by paste or sealing wax throw in a small globule 

 of mercury to act as a valve then boil the mercury, holding the 

 tube vertically over the flame of the spirit lamp, and surrounding the 

 tube with thick folds of paper, protecting the fingers still farther by a 

 glove. 



(/.) When the mercury boils quietly, and the ball is readily filed on 

 being withdrawn from the heat, we presume that the air is all expelled. 



* If the bore be very small, the mercury must be introduced by the elastic gum 

 bottle, by tying it fast compressing it strongly with the hand to expel the air, and 

 then allowing it to resume its former shape, when a portion of mercury will rise 

 into the tube. 



t See American Journal. Vol. IV, pa. 398, for the method of Mr. Kendal, a self- 

 fought artist. 



