GAS, COAL 



567 



meter in the stand o. i is an indentation in which the lower end of the eudiometer 

 rests, so as to prevent its falling into the deeper portion of the trough A. When in 

 use the trough is filled with quicksilver to within an incli of the upper edge of tlio 

 glass plates c c, about 30 to 35 Ibs. of the metal being necessary for this purpose. 



The eudiometers or measuring-tubes, should be accurately calibrated and graduated 

 into cubic inches and tenths of a cubic inch, the tenths being subdivided by the eyo 

 into hundredths, when the volume of gas is read off; this latter division is readily 

 attained by a little practice. At each determination of volume, it is necessary that 

 the gas should either bo perfectly dry, or quite saturated with moisture. The first 

 condition is attained by placing in the gas, for half an hour, a small ball of fused 

 chloride of calcium, attached to a platinum wire 1 ; the second condition, by introduc- 

 ing a minute drojp of water, into the head of the eudiometer, before filling it with 

 quicksilver. The determinations of volume must either be made when the mercury 

 is at the same level inside and outside the eudiometer, or, as is more frequently 

 done, the difference of level must be accurately measured and allowed for in the 

 subsequent reduction to a standard pressure. The height of the barometer and the 

 temperature of the surrounding atmosphere must also be observed each time the 

 volume of gas is measured, and proper corrections made for pressure, temperature, 

 and also the tension of aqueous vapour, if the gas be moist. As tables and rules for 

 these corrections are given in most treatises on chemistry, they need not be repeated 

 here. 



These troublesome corrections 1025 



and calculations can be avoided 

 by employing an instrument in- 

 vented some years ago by Dr. 

 Frankland and Mr. W. J. Ward, 

 and which not only does away 

 with the necessity for a room 

 devoted exclusively to gaseous 

 manipulations, but greatly 

 shortens and simplifies the 

 whole operation. This instru- 

 ment, which is represented by 

 fig. 1025, consists of the tripod A, 

 furnished with the usual level- 

 ing screws, and carrying the 

 vertical pillar BB, to which is 

 attached, on the one side, the 

 moveable mercury trough c, with 

 its rack and pinion a a, and on 

 the other, the glass cylinder D D, 

 with its contents. This cylinder 

 is 36 inches long, and 4 inches 

 internal diameter ; its lower ex- 

 tremity is firmly cemented into 

 an iron collar c, the under sur- 

 face of which can be screwed 

 perfectly watertight upon the 

 bracket plate d by the interposi- 

 tion of a vulcanised caoutchouc 

 ring. The circular iron plate d 

 is perforated with three aper- 

 tures, into which the caps e, e, e, 

 are screwed, and which com- 

 municate below the plate with the 

 T-piece E E. This latter is fur- 

 nished with a double-way cock/, 

 and a single-way cock g, by means 

 of which the tubes cemented into 

 the sockets e, e, e, can be made to communicate with each other, or with the exit pipe A 

 at pleasure. 



1 These balls, which should bo of the size of a large pea, are required constantly in operations upon 

 gases ; they are readily prepared, when the substances of which they are formed is fusible by heat, 

 as chloride of calcium or caustic potash, by melting these materials in a crucible and then pouring 

 them into a small bullet-mould, in which the curved end of a platinum wire has been placed ; when 

 quite cold the ball attached to the wire is readily removed from the mould. Coke bullets are made 

 by filling the mould containing the platinum wire with a mixture of two parts of coke and one of 

 coal, both finely powdered, and then exposing the mould and its contents to a heat gradually increased 

 to redness, for a quarter of an hour. 



