AN ELECTROLYTIC AERATOR 



JOHN P. PUTNAM 



Massachusetts Institute of Technology 



1 



To those over-zealous aquarists who 

 are wont to overstock their tanks, I sub- 

 mit a device which I believe may be of 

 use. Nature's method of providing oxy- 

 gen for the inhabitants of water cannot 

 be improved, but Nature never intended 

 large numbers of fishes to live in small 

 receptacles. We cannot, therefore, ex- 

 pect her to produce a plant that will com- 

 pete quantitatively with the oxygen gen- 

 erator. Commercially the purest oxygen 

 is generated by electrolysis. I have ac- 

 cordingly applied this method of produc- 

 tion to the problem of aeration. 



Electrolysis is in effect the interchange 

 of ions brought about by the passage of 

 an electric current through a liquid. Or, 

 looking at it from another point of view, 

 these ions carry minute charges of elec- 

 tricity. Chemically pure water is but 

 slightly ionized, and therefore does not 

 conduct electricity appreciably. Tap 

 water, however, contains salts which are 

 ionized, and is, in a limited extent, a con- 

 ductor or electrolyte. 



Water is composed of two gases — 

 hydrogen and oxygen — in the proportion, 

 by volume, of two to one. Hydrogen is 

 an inert gas. I believe it has no physio- 

 logical effect other than that of ''blanket- 

 ing" the oxygen, as does the nitrogen of 

 the air. When a current of electricity is 

 passed through water it is split up into its 

 chemical constituents, hydrogen and oxy- 

 gen. It is the latter gas which is of vise 

 in aeration, so the former may be dis- 

 carded. 



During electrolysis the ionized salts 

 dissolved in the water are also split up ; 

 thus acid is formed at the positive pole or 



anode, while alkali appears at the cathode. 

 If the acid and alkali are allowed to mix 

 they will recombine to form the same 

 salts originally present in the water. This 

 must be accomplished if the chemical con- 

 stituency of the water is not to be altered. 



The device I have mentioned consists 

 of a glass tube about one centimeter in 

 diameter, expanding below into an in- 

 verted cup, which is open at the bottom. 

 This cup fits down into another glass cup, 

 open at the top, leaving a clearance be- 

 tween the two of about two or three milli- 

 meters. The two are held together with 

 wedges of cork. The oxygen is gene- 

 rated at a ring of coiled platinum wire 

 encircling the inverted cup just above its 

 rim. Bubbles of this gas rise up between 

 the two cups, through the water of the 

 aquarium, to the surface. The hydrogen, 

 evolved from a similar ring just inside the 

 inverted cup, passes up the glass tube 

 and escapes. The electricity reaches 

 these rings along copper wire leads, sealed 

 in small glass tubes. It passes from the 

 outside ring under the rim of the inverted 

 cup to the inner one. The acid and alkali 

 become thoroughly mixed in the bottom 

 of the outside cup. This cup also pre- 

 vents the fishes from coming in contact 

 with the electrodes. 



As electrolysis procedes the water 

 within the glass tube becomes slightly 

 alkaline and, in consequence, the water 

 outside of the tube becomes correspond- 

 ingly acid. For this reason, when the 

 apparatus is first set up, it is best to put 

 one drop of caustic soda into the glass 

 tube. This should be done but once. 



I have figured that with electrical en- 



