II. TEACHING (PURE). 511 



The apparatus, which is represented by the accompanying figure, consists 

 of the tripod A furnished with the usual levelling screws, and carrying the 

 vertical pillar B, B, to which is attached, on the one side, the movable 

 mercury trough C, of gutta perch a, 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 3 inches in diameter, its lower extremity is cemented into an iron 

 collar, e, the under surface of which can be screwed perfectly water-tight 

 upon the bracket-plate, d, by the interposition of a vulcanised caoutchouc 

 ring. The circular iron plate d is perforated with two large apertures for the 

 passage of the tubes E and F, besides a smaller one into which the brass 

 cock b is screwed. E is a glass tube of uniform bore, and about 18 mm. 

 internal diameter, and marked with 10 divisions equidistant from each other. 

 It serves to contain the gas during measurement. Its upper extremity 

 terminates in the capillary tube e, which carries a glass stop-cock, and is 

 cemented into the steel cap /in such 'a way as to exclude any air space. For 

 the passage of the electric spark, two -platinum wires are fused into E at g. 

 At its lower extremity the tube E, after passing water-tight through a 

 caoutchouc cork in the plate rf, is connected with the junction piece h. 



F is a second glass tube only 5 mm. internal diameter, graduated with a 

 millimetre scale throughout its entire length, and reaching to a height 'of 

 about 8 inches above the glass cylinder. It is furnished at top with a small 

 funnel, z, into the neck of which a glass stopper, about 2 mm. in diameter is 

 carefully ground. In this tube the pressure of the gas in E is measured. 

 Like E, it also passes water-tight through the plate d, and is connected with 

 the junction piece //, which is furnished with a stop-cock, and is continued to 

 the floor, where it is connected by a long caoutchouc tube with the glass 

 mercury reservoir G. The caoutchouc tube is 3 mm. internal diameter, and 

 is strengthened by a jacket of tape to enable it to withstand the pressure of 

 mercury. The reservoir G can be raised or lowered by the cord and pulley 

 k, I. H is an absorption tube, in which the gases are brought into contact 

 with various liquid or solid re-agents. It is supported on the clamp o, and 

 connected with the capillary tube e, by the cap and j unction clamp p. 



The tubes E, F, are held firmly in position by the clamp m, which is screwed 

 to the under side of the plate d. 



Before using the apparatus, the cylinder D, D is filled with water through 

 the cock b, and a slow stream is afterwards established through the syphon 

 n, one leg of which encloses the upper part of the tube F. The internal walls 

 of the tubes E and F are, once for all, moistened with distilled water by the 

 introduction of a few drops into each, through the stop-cock on e and the 

 stoppered funnel z. The reservoir, -previously filled with mercury, is now 

 placed in communication with the tubes E and F, and is raised until the 

 mercury flows from the cock on c, which is then shut, and rises into the cup 

 z, the stopper of which is then firmly closed. The absorption tube I, being 

 now filled with quicksilver, and attached to e by the Screw clamp p, the 

 instrument is ready for use. 



With a proper supply of water the temperature of the gas remains constant 

 during the entire analysis, and therefore no correction on that score has to be 

 made. The atmospheric pressure being altogether excluded from exercising 

 any influence upon the volumes or pressures, no barometrical observations are 

 requisite ; and as the tension of aqueous vapour in E is exactly balanced by 

 that in F, the instrument is in this respect self correcting. 



The readings of pressures in this instrument give, without any calculation 

 or correction, the true volumes of the gases, and as the manipulations are very 

 simple, the analysis of even a complex gaseous mixture is made very rapidly. 

 Thus the determination of the separate constituents of a mixture of carbonic 

 anhydride, oxygen, hydrogen, carbonic oxide, marsh gas, and nitrogen can be 

 made in about two hours. 



