DECOMPOSITION OF WATER. 



Thus it appears, the tubes being of equal capacity, that the 

 volumes of the two gases produced are in the proportion of 2 

 to 1, the volume of hydrogen being twice that of oxygen. 



It will be further observed, that continually throughout the pro- 

 cess of the experiment, the same proportion is maintained between 

 the volumes of the gases evolved. At every stage of the process, 

 the volume of hydrogen, c F, evolved, is found to be exactly double 

 that of the oxygen, A E. 



But a comparison of the weights of these two gases, bulk for bulk, 

 proves that oxygen is sixteen times heavier than hydrogen. It 

 follows from this that the weight of the double volume of hydrogen 

 evolved in the experiment here described, will be exactly one-eighth 

 of the single volume of oxygen simultaneously evolved. 



Thus it appears that the water is decomposed by the voltaic cur- 

 rent, and that its constituents are the gases oxygen and hydrogen, in 

 the proportion of 8 parts by weight of oxygen to 1 of hydrogen. 



46. Certain metals which are obtained in the laboratories of 

 chemists, though unknown in the arts, such as potassium and 

 sodium, have so strong an attraction for oxygen that they cannot be 

 exposed in the atmosphere without spontaneously combining with 

 that constituent of it. If a piece of one of these metals be plunged 

 in water, it will exert an attraction on the oxygen of the water so 

 powerful as to separate it from, the hydrogen. The oxygen will, 

 in virtue of this attraction, desert the hydrogen, and, combining 

 with the potassium or the sodium, will form potash or soda, while 

 the hydrogen, disengaged in the form of gas, may be collected in a 

 glass receiver in the usual way. If the potash or soda thus pro- 

 duced be weighed, it will be found to be heavier than the potassium 

 or sodium, by the weight of the oxygen which has entered into 

 combination with it, and this excess of weight will be exactly 

 eight times the weight of the hydrogen which is disengaged ; from 

 which it follows as before that water consists of 8 parts by weight 

 of oxygen and 1 of hydrogen. 



47. None of the metals commonly used in the arts have an 

 attraction for oxygen sufficiently energetic to effect thus sponta- 

 neously the decomposition of water. The attraction, however, of 

 some of them iron, for example may be so exalted by elevation 

 of temperature that it may, by means of certain arrangements, 

 produce a like effect. 



An apparatus for the decomposition of water, by means of 

 heated iron, is represented in fig. 4. 



A porcelain tube, a 6, the middle part of the length of which is 

 filled with fragments of fine iron wire, is inserted across a furnace, 

 by means of which the tube may be heated, so that the iron 

 it contains shall be red-hot. One end, a, communicates by a 



111 



