Various Forms of the Volta-electromcter. 173 



to the mouths of the tubes as was consistent with the safe col- 

 lection of the gases evolved. In certain cases, where it was 

 required to evolve the elements upon as small a surface as 

 possible, the metallic extremity, instead of being a plate, con- 

 sisted of the wire bent into the form of a ring (fig. 6.). 

 When these tubes were used as measurers, they were filled 

 with the dilute sulphuric acid, and inverted in a basin of the 

 same liquid (fig. 7.), being placed in an inclined position, with 

 their mouths near to each other, that as little decomposing 

 matter should intervene as possible; and also, in such a direc- 

 tion that the platina plates should be in vertical planes (720.). 



708. Another form of apparatus was that delineated (fig. 8.). 

 The tube is bent in the middle ; one end is closed ; in that 

 end is fixed a wire and plate, a, proceeding so far downwards, 

 that, when in the position figured, it shall be as near to the 

 angle as possible, consistently with the collection, at the closed 

 extremity of the tube, of all the gas evolved against it. The 

 plane of this plate is also perpendicular (720.). The other 

 metallic termination, b, is introduced at the time decomposi- 

 tion is to be effected, being brought as near the angle as pos- 

 sible, without causing any gas to pass from it towards the 

 closed end of the instrument. The gas evolved against it is 

 allowed to escape. 



709. The third form of apparatus contains both electrodes 

 in the same tube; the transmission, therefore, of the electri- 

 city, and the consequent decomposition, is far more rapid than 

 in the separate tubes. The resulting gas is the sum of the 

 portions evolved at the two electrodes, and the instrument is 

 better adapted than either of the former as a measurer of the 

 quantity of voltaic electricity transmitted in ordinary cases. 

 It consists of a straight tube (fig. 9.) closed at the upper ex- 

 tremity, and graduated, through the sides of which pass the 

 platina wires (being fused into the glass), which are connected 

 with two plates within. The tube is fitted by grinding into 

 one mouth of a double-necked bottle. If the latter be one 

 half or two thirds full of the dilute sulphuric acid, it will, upon 

 inclination of the whole, flow into the tube and fill it. When 

 an electric current is passed through the instrument, the gases 

 evolved against the plates collect in the upper portion of the 

 tube, and are not subject to the recombining power of the 

 platina. 



710. Another form of the instrument is given at fig. 10. 



711. A fifth form is delineated (fig. 11.). This I have 

 found exceedingly useful in experiments continued in succes- 

 sion for days together, and where large quantities of indicat- 

 ing gas were to be collected. It is fixed on a weighted foot, 



