VOLTAIC BATTERIES MAY BF USED FOR PRODUCING GREAT PRESSURE. 49 



the operator to tie it on so that no leakage shall occur between the India-rubber and 

 the glass, even under the severest pressures. When the gauge shows that the required 

 degree of condensation is arrived at, the connexion with the battery is broken, and the 

 condensation, of course, stops ; the siphon being carried to the mercurial trough, taking 

 care to keep its position erect, its short limb is depressed under the mercury, and car- 

 ried into a jar containing the sulphurous acid. If, under these pressures, any of the 

 acid gas finds its way into the condensed air, its presence is detected by the reddening 

 of the blue litmus water. It is necessary here to observe, that the indications of the 

 air gauge do not give a correct estimate of the amount of condensation, but always rep- 

 resent them higher than they are according to Marriotte's law : it has long been known 

 that the volume of gas dissolved by water depends, in a great measure, on the pressure 

 exerted on it : now it will be found, when the operation is conducted in an instrument 

 arranged as this, that a rery large proportion of the air in the gauge disappears in this 

 manner; its zero point is therefore altered, and the condensation appears higher than it 

 really is. It may be remarked, in passing, that it is surprising to what an extent the 

 absorption of oxygen and hydrogen is carried in the longer leg, owing to their making 

 their appearance in a nascent form. To ascertain the true condensation, so soon as 

 the passage of the sulphurous acid or other gas has taken place satisfactorily, the mem- 

 brane is to be punctured with a pin, and when a pneumatic equilibrium is obtained, the 

 height of the liquid in the gauge will mark the point where the zero of the scale should 

 be placed. 



156. Some might suppose that there is danger in making use of an apparatus like 

 this, where a high pressure is produced, owing to the risk of an explosion of the com- 

 pound gases in the long limb, since it is stated in most works on chemistry that a mix- 

 ture of oxygen and hydrogen, when compressed, will explode. To ascertain if there 

 was any danjer arising from this, as also to know to what extent the condensation could 

 be pushed by the aid of a voltaic battery, I took a tube, a b (Jig. 20), and into the closed 

 extremity having fused a pair of platinum wires, and drawn the other into a long capil- 

 lary tube, bending it at the same time at right angles to the former, I filled it with water 

 (boiled until all the air mechanically enclosed in it was expelled), except a portion of the 

 narrow capillary part from d to c, which contained atmospheric air, to act as a gauge ; 

 the extremity, c, was closed. Next the platina wires were made to communicate with 

 the poles of an active voltaic battery of 120 pairs, and gas slowly accumulated, the cur- 

 rent of electricity steadily passing all the time, as was indicated by the deviations of a 

 galvanometer, through which it was made to circulate. Observations were made every 

 few minutes on the progress of the experiment, the last of which indicated a pressure of 

 slightly upward of forty-three atmospheres, and shortly after it was taken the tube burst; 

 not, however, on account of the explosion of the gaseous materials in it, but because it 

 could not sustain so excessive a pressure tending to burst it, a pressure equivalent to that 

 of a column of mercury nearly thirteen hundred inches high. 



157. These results lead us to some remarkable conclusions in relation to the passage 

 of voltaic currents. Dr. Faraday found that they cannot pass along such media as 

 water without effecting its decomposition ; in fact, that the transfer of elements seemed 



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