FILLING BAROMETER TUBES. 439 



ON FILLING BAROMETER TUBES. 



[Having been frequently called upon by our correspondents to give information relative to 

 filling barometer tubes, we requested Mr. James Green, of New York, and Mr. W. Wiede- 

 mann, of Washington, to furnish us with an account of the methods employed by them. 

 The following are their answers to our request, with additional information from the Trans- 

 actions of the Royal Society. — J. H.] 



I. — By James Green, of New York. 



One of the greatest difficulties with the inexperienced is to get the 

 tube itself clean and free of moisture. If the tube is foul, the com- 

 mon way is to clean it with a covered copper wire, wrapped with 

 additional cotton at the end to fit the tube, and moistened with alcohol 

 and whiting at first, afterward with dry cotton. If the tube can be 

 heated and air blown in dry, so much the better. 



The mercury and tube should be heated as much as will be allow- 

 able to handle them, to keep all the water in a state of vapor. The mer- 

 cury is filtered into the tube in a long paper funnel, in a fine stream, 

 until within a quarter of an inch of the top. The tube will now be 

 found covered with small air bubbles. Stop the end of the tube with 

 the finger, and run a large air bubble up and down the tube. This 

 will collect the small ones together. Provided the tube be clean and 

 dry, and mercury pure, a pretty good result is obtained. 



To boil the mercury in the tube, fill within three inches of the top. 

 Then, with a clear charcoal fire or long spirit lamp, warm the whole 

 tube as much as you can without inconvenience. The tube being held 

 by a cloth, (with woollen gloves on hands is well,) then commence at 

 the top or open end and hold the tube over the fire until the mercury 

 boils, moving the tube a little in all directions all the time to equalize 

 the distribution of the heat from the fire. Continue the boiling 

 downwards until 3011 reach the end, and then return boiling up to the 

 top again. Some begin at the closed end, (for economy of risk and 

 labor,) and boil up only. This may answer the purpose, but not so 

 well as the other, particularly if the tube is not perfectly dry and 

 clean. The part of the tube unoccupied will be well-prepared by 

 the boiling mercury bubbling up; so that to complete the filling, filter 

 hot mercury to the top. 



The more perfect methods of boiling are impracticable out of the 

 workshop and hands of the glass-blower. 



One of the best tests for the purity of the mercury is, that after 

 once filtering in a long paper funnel to get it clean, in filtering again 

 slowly no lines or marks are left on the paper by the receding sur- 

 face, and in motion no strings or tails are made, but the mercury will 

 be rounded at its edges. 



The best method ordinarily practicable for purifying mercury is to 

 put it in a large bottle with some very dilute nitric acid, and shake it 



