306 EXPERIMENTAL INVESTIGATIONS. 



THE BAKERIAN LECTURE. ON CERTAIN PHE- 

 NOMENA OF VOLTAIC IGNITION AND THE DE- 

 COMPOSITION OF WATER INTO ITS CONSTITUENT 

 GASES BY HEAT. 



Phil. Trans., R.S. Received September 3. Read November 19, 1846. 



IN the 'Philosophical Magazine' for August 1841, I recom- 

 mended for eudiometrical purposes the use of a platinum 

 wire ignited by a voltaic battery. In fig. i, is represented 

 a form of apparatus for this purpose ; it consists of a tube of 

 Bohemian glass, with a loop of platinum wire -^th of an inch 

 diameter sealed into its upper end ; the size of the glass tube 

 may be adapted to the quantity of gas sought to be analysed, 

 and may, when necessary, be reduced to extremely small 

 dimensions, one-eighth of an inch being ample ; into this the 

 gas may readily be made to ascend, by the insertion of a wire 

 of copper, platinum, or glass, as may be suitable to the gas ; 

 two cells of the nitric-acid battery are sufficient fully to ignite 

 the wire, and the same battery supplies, by electrolysis, pure 

 oxygen and hydrogen for the analysis. Since the period 

 when I first proposed this I have seldom used any other 

 apparatus for such gaseous analyses as are performed by 

 combining the gas to be examined with oxygen or hydrogen. 

 This eudiometer possesses the advantage of enabling the 

 operator either to detonate or slowly to combine the gases, by 

 using different powers of battery, by interposing resisting 

 wires, or by manipulation alone a practised hand being able, 

 by changing the intervals of contact, to combine or detonate 

 the gas at will. My general practice has been to produce a 

 gentle heat in the wire until the gases contract, and then 

 gradually to increase the heat until a full ignition takes place, 

 by which means all the objects of the eudiometer of Volta are 

 fulfilled, without detonation, without dependence on the fickle 

 electric spark, and without thick tubes, danger of explosion, 

 or of the gases being projected from the eudiometer. 



I have commenced with a description of this eudiometer, 



