1835.] 'Filling Barometers. s 441 



rect instrument thus placed within the reach of every 

 practical chemist. The detail may be as follows : 



Provide 1. A clean barometer tube, not less than -J inch 

 bore at the closed end, but which may run away to ^th at 

 the lower end, to save mercury, and not less than 33 inches 

 long. 



2. A tube 8 or 9 inches long, -^ or f bore, open at both 

 ends, one end being drawn out to a fine aperture ; for pour- 

 ing in the mercury. 



3. Four or five pounds of mercury, (8 or 10 lbs. would 

 be more convenient) which has been standing three or four 

 weeks under weak nitric acid, (1 acid to 10 water) ; or 

 distilled mercury if to be had. 



4. An iron ladle, and a disc of sheet iron which will not 

 quite cover the mercury, when in the ladle. 



5. A small wedgewood mortar, which the mercury will 

 i or I fill. 



6. A turned wood box and lid, (such as are used for tooth 

 powder), not less than 1^^ inch internal diameter and depth; 

 which must have a hole through the lid large enough to 

 slide up and down the tube, and be varnished inside and 

 out, for the cistern. 



The tube should be dried over a lamp or before a fire, 

 with the open end up, and covered with a bit of muslin to 

 keep out dust. In the mean while the mercury may be 

 placed in the ladle, with the iron disc floating upon it ; and 

 set on the fire till it boils, when it is to be instantly removed 

 and placed in the cold. Whilst it is cooling, a horse hair 

 must be passed quite down the tube to the closed end, or if 

 one is not long enough, two may be bound together with a 

 fibre of silk. A knot makes a difficulty in passing them 

 down. A fine silked thread, waxed to give it stiffness will 

 do, but the tube must then be cold first.* 



As soon as the mercury is cold enough to handle, it is to 

 be poured into the wedgewood mortar, and the pouring 

 tube (2) having its point dipped below the surface to ex- 

 clude dust, is to be filled to about an inch by suction applied 



• Wire does not answer, the tubes being very subject to snap after it, even 

 when silked. 



