Prof. J. P. Cooke on Lecture Experiment* 



51 



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lected by displacement in a precisely similar jar mounted as 

 represented in fig. 3. The Fig. 3. Fig. 4. 



mouth of this jar is closed by = 

 a ground glass plate which 

 is tubulated, as is shown in 

 detail by fig 4. This tubu- 

 lature, again, is closed by a 

 rubber stopper through which 

 pass, first the delivery-tube, 

 which reaches the bottom of 

 the jar, and secondly an over- 

 flow tube, which merely passes 

 through the stopper, and 

 which in the experiment 

 should be connected by a 

 flexible hose with a ventila- 

 tor. When a larger amount 

 of chlorine is desired, the 

 first jar may be connected 

 with a second, and that with a third, &c, all mounted in the 

 same way, and the exit-tube from the last jar leading to a venti- 

 lator as before. When the jars are full, the tubulated stoppers 

 with their connexions are removed and a plain glass cover sub- 

 stituted. This simple form of apparatus will be found very use- 

 ful in all experiments on gases heavier than the air. 



During the process of electrolysis the class will see that the 

 two gases are evolved in nearly the same proportions, the co- 

 loured gas rising in one jar as rapidly as the water falls in the 

 other. The narrowness of the jar prevents to a great degree 

 the diffusion of the chlorine ; and a piece of white paper placed 

 behind the jar will make the line between the coloured gas and 

 the air visible to a considerable distance. When the jars are 

 full, the qualities of the two gases may be made evident by ap- 

 propriate experiments. As is well known, the gases will not be 

 delivered in atomic proportions until the liquid acid is saturated 

 with chlorine. It is best, therefore, not to empty the cell after 

 the experiments, but, having removed the rubber stoppers with 

 their attachments, to close the mouth with the ground glass 

 stoppers, and the apparatus will then be ready for the next oc- 

 casion. It is also best to interpose a small wash-bottle contain- 

 ing sulphuric acid between the cell and the chlorine-jar; for 

 this will not only dry the gas, but also equalize the hydrostatic 

 pressure on the two delivery-tubes. Decomposing-cells like 

 that represented in fig. 1, and all other forms of glassware de- 

 scribed in this paper, are made by the New England Glass-Com- 

 pany of East Cambridge, and can be ordered through any of the 



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