392 Mr. T. Gray on the Electrolysis 



and more might easily be added ; hence the point to be de- 

 cided is whether the oxidation and loss in the solution can be 

 avoided or their effects eliminated. As the result of a good 

 deal of experience, it appears to me that the first objection is 

 of very little weight indeed, as the plate need not be sensibly 

 oxidized in the process of washing and drying if even ordinary 

 care is taken in the operation. The loss by corrosion in the 

 liquid leads to results which depend to some extent on the size 

 of the plate and the temperature of the solution ; and a great 

 many experiments have been made on the effect this may have 

 on the apparent value of the electrochemical equivalent in dif- 

 ferent cases. Examples of such experiments are given below, 

 and they are there discussed more in detail ; but it may be 

 stated here that the effect can be fairly well allowed for if 

 the size of the plate and the strength of the current, as well 

 as the state of the solution, are known. The error due to this 

 cause need never exceed a tenth per cent., and will generally 

 be considerably less than that. 



It appears from experiments on the loss of copper in solu- 

 tions of sulphate of copper, that a strong solution of normal 

 pure sulphate is at ordinary atmospheric temperature even 

 more active in dissolving copper than the same solution when 

 as much as 5 per cent, of acid has been added ; but that in the 

 use of the normal solution there is a danger that the presence 

 of the copper plates in the cell may render the solution satu- 

 rated with copper, after which a rapid oxidizing action takes 

 place which invariably causes the gain of weight in an electro- 

 lysis experiment to be too great. The deposit in such a case is 

 of a darker colour than when the solution is kept sufficiently 

 acid ; and indeed a bad plate can generally be detected by 

 simple inspection, but it is well always to add such a quantity 

 of acid (a very little is sufficient) as will prevent any un- 

 certainty on the subject. 



Electrolytic Cells. — Some of the arrangements which have 

 been found convenient for the electrolytic cells are illustrated 

 in figs. 1 to 6. They consist, in the smaller sizes, of round 

 glasses into which three plates, arranged with their planes 

 parallel and about one centimetre apart, are held by means of 

 clips of stiff platinoid or brass wire of the form shown in figs. 

 2 and 3. The outer clips are connected together by a cross 

 piece, a (fig. 1), at the top, but are insulated from the middle 

 clip by a block of vulcanite, fixed in the cross piece, b, into 

 which they are all tightly fitted. These clips are very con- 

 venient, and are easily made by taking a piece of stiff wire, 

 bending it nearly close at its middle point, then winding each 

 half two or three times round a rod of metal of suitable size 



