Description of a new Mercurial Trough. 



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collected, — quantities often insufficient for the desired experi- 

 ments. With a view to obviate this inconvenience, I have 

 modified the mercurial trough, so as to be able, without sacri- 

 ficing ceconomy, to collect considerable quantities of gas; and 

 I have thought it may be of use to give a description of this 

 new instrument, for the service of persons engaged in parti- 

 cular researches. This apparatus is formed of a small oblong 

 oak box, to the bottom of which is cemented a glass, which 

 fits exactly over its whole extent. The external surface of 

 this glass is carefully polished and prepared. In the centre of 

 one of its small sides (it is rectangular), is worked a narrow 

 and deep groove parallel to the large sides of the right angle. 

 This opening corresponds to a hollow in the bottom of the 

 box. This being done, I arrange the apparatus in the fol- 

 lowing way, when I desire to collect a gas over the mercury : 

 — I procure bell-glasses made of emery-stoppered bottles, the 

 bottom of which is removed ; the edges of these receivers are 

 prepared and rubbed with emery, and apply accurately to the 

 ground glass, precisely like the receiver of an air-pump. The 

 edges may be very slightly greased, or this precaution may 

 be dispensed with. The receiver is placed on the ground 

 glass, where it is kept fixed with one hand ; with the other 

 hand the stopper is removed, and it is entirely filled with mer- 

 cury ; then it is carefully re-stopped. This being done, a 

 small quantity of mercury is poured into the box, so as to fill 

 the small cavity, and to cover its bottom with a stratum of 

 some millimetres. The receiver may now be moved in all di- 

 rections, and may be slid until it is over the small cavity, 

 into which the extremity of the curved tube by which the gas 

 is disengaged, is adapted. To one of the angles of the box 

 may be fitted a small pure iron stopcock, by which the mer- 

 cury is drawn off when the operation is ended. For greater 

 clearness, I subjoin a figure, which represents this new trough 

 of the dimensions which I have adopted. 



A B = 4£ centimetres *. B C = 23 centimetres. C D = 17 centimetres. 

 Depth of the longitudinal groove, taken above the glass plate, = 2 cen- 

 timetres. 



• The centimetre is = 0-393708 of a English inch. 



