to our present expression, enters:  it is the negative extremity of the decomposing body; is where oxygen, chlorine, acids, &c., are evolved; and is against or opposite the positive electrode.  The cathode is that surface at which the current leaves the decomposing body, and is its positive extremity; the combustible bodies, metals, alkalies, and bases, are evolved there, and it is in contact with the negative electrode.

[A] [Greek:  ano] upwards, and [Greek:  -odos] a way; the way which the sun rises.

  [B] [Greek:  kata] downwards, and [Greek:  -odos] a way; the way
  which the sun sets.

664.  I shall have occasion in these Researches, also, to class bodies together according to certain relations derived from their electrical actions (822.); and wishing to express those relations without at the same time involving the expression of any hypothetical views, I intend using the following names and terms.  Many bodies are decomposed directly by the electric current, their elements being set free; these I propose to call electrolytes.[A] Water, therefore, is an electrolyte.  The bodies which, like nitric or sulphuric acids, are decomposed in a secondary manner (752. 757.), are not included under this term.  Then for electro-chemically decomposed, I shall often use the term electrolyzed, derived in the same way, and implying that the body spoken of is separated into its components under the influence of electricity:  it is analogous in its sense and sound to analyse, which is derived in a similar manner.  The term electrolytical will be understood at once:  muriatic acid is electrolytical, boracic acid is not.

  [A] [Greek:  elektron], and [Greek:  lyo], soluo.  N. Electrolyte, V.
  Electrolyze.

665.  Finally, I require a term to express those bodies which can pass to the electrodes, or, as they are usually called, the poles.  Substances are frequently spoken of as being electro-negative, or electro-positive, according as they go under the supposed influence of a direct attraction to the positive or negative pole.  But these terms are much too significant for the use to which I should have to put them; for though the meanings are perhaps right, they are only hypothetical, and may be wrong; and then, through a very imperceptible, but still very dangerous, because continual, influence, they do great injury to science, by contracting and limiting the habitual views of those engaged in pursuing it.  I propose to distinguish such bodies by calling those anions[A] which go to the anode of the decomposing body; and those passing to the cathode, cations[B]; and when I have occasion to speak of these together, I shall call them ions.  Thus the chloride of lead is an electrolyte, and when electrolyzed evolves the two ions, chlorine and lead, the former being an anion, and the latter a cation.