6 Mr. J. Swinburne on some 



chemists regard as such valuable reagents, do not exist. What 

 is the evidence in favour of the existence of nascent hydrogen ? 

 If some such metal as magnesium, or sodium amalgam, is put 

 in dilate acid, bubbles come off. Many other metals act simi- 

 larly. If such a compound as persulphate of iron is put in, too, 

 it is reduced to proto-sulphate. From frequently observing 

 effervescence when reduction is effected, it is easy to assume 

 the effervescence is the cause of the reduction. The theory is 

 that the energy supplied first produces hydrogen. A power- 

 ful attraction has just been overcome, and has been satisfied 

 neither by combination with more hydrogen nor otherwise. 

 The hydrogen then seizes on the persalt of iron, and takes 

 away some of the acid radical, forming free acid, which in its 

 turn acts on the oxide of the metal. This action is secondary, 

 and may be supposed to evolve heat. There is thus waste of 

 heat, and the cell is irreversible. A better explanation would 

 be, that the metal can dissolve if it either reduces the persalt or 

 evolves hydrogen. The reduction of the persalt needs less 

 energy, so that takes place. When there is no reducible salt 

 available, hydrogen is evolved ; and as it has to be expanded 

 into the gaseous form, a good deal of work has to be done on 

 it. Evolution of hydrogen and reduction of the salt are thus 

 alternate, not consecutive results. Similarly in an engine — 

 the steam either works the engine or comes out at the safety- 

 valve ; it does not begin to lift the safety-valve, and then 

 change its mind and work the engine in a nascent state. It 

 must be remembered that the term oxidize has come to denote 

 many other things than adding oxygen. For instance, adding 

 any electronegative radical is called oxidizing. If sulphur 

 had been as common as oxygen, no doubt we should always 

 talk of sulphurizing. The use of the ,term " oxidize " has 

 also led to the tacit assumption that in electrolysis the water 

 is electrolysed and the other results are secondary actions of 

 electrolytic oxygen and hydrogen. If there were such a 

 thing as nascent hydrogen, putting a depolarizer, such as 

 nitric acid, round the carbon plate of a Bunsen cell w r ould not 

 increase its electromotive force ; it would merely make it heat 

 more on discharge. 



So far the cells considered have been reversible. It does 

 not follow that a cell is always reversible, but, if not, there is 

 at least one non-adjuvant action. As a good example of non- 

 reversibility, aluminium and its solutions may be taken. 

 Aluminium does not dissolve in dilute nitric or sulphuric 

 acid, yet it cannot be deposited electrically, from any 

 known solution. Aluminium and carbon in nitric acid give 

 only a small fraction of a volt. 



