The Daniell Cell

Radio Record, Volume VIII, Issue 27, 11 January 1935, Page 43

The Daniell Cell

Primary Battery or Charger

"THE Daniell cell is a primary battery which requires no recharging, an‘ which can be used either as a battery charger or as an "A" battery for the set. It will not supply much current -between a ¢ and 4 amp-and requires constant attention. Each complete. unit of the Daniell cell battery should deliver approximately: one volt, and if the unit is to be used as a battery charger, several celis in excess of the required voltae must be provided. If it is desired to ycharge a six-volt accumulator; nine to ‘ten cells should be provided. To charge a 4-volt battery, six to eight will be needed, and for a 2-volt, four. If, how- _ ever, the battery is to work directly on ‘to the set, it is necessary only to provide one or two extra cells, and to control the voltage with a‘ rheostat. Ib this case a voltmeter must be used on the set side of the rheostat in order that the voltage should not exceed that required by the valves. For each cell a glass jar is required, at least three inches wide at. the mouth. The telephone type of glass Leclanche containers are the best, but anything will do providing it is about the size of a 2lb. jam jar; in fact, one of these would do quite well if the top were cut off to allow the porous pot to be inserted.

One porous pot percell; These ean be obtained at the price of 6d. each upon application to the Stores Manager of the Post and Telegraph Department, Wellington, or the Chief Postmaster, Christchurch. A quantity of copper sulphate, or. as it is better known, bluestone. Tor eight or nine cells, two Ibs. will be required every fortnight. Sulphurie Acid. This should be obtained from a chemist who selis it 99 per cent. pure. .If this is used, one part in sixty to eighty parts of water by weight will make’ a. sufficientiy strong solution, The amount will vary with the number of cells to be used;' five cells require about 1 fluid oz. of pufe sulphuric. A quantity of copper sheet, 20-24 gauge. A quantity of scrap zine, which can be obtained from any foundry or the "tin" lining of packing cases. Distilled or pute rain’ water collected in an earthenware jar, . An ounce of mercury to each pot. This is not essential, but it lengthens the life of the zinc. ) Scrap zinc is melted down and . moulded into rods 7-8ths of an inch thick and long enough to clear -the porous pot, While in the mould, push in a terminal taken from an old "A" cell. This has a long shank and will make good contact with the zinc. Otherwise use copper. wire, which should be long enough to connect with the copper of the next cell. Those who do not wish to make their own zincs can obtain them ready made. As these have been amalgamated the use of mercury will be unnecessary. The thicker rods, which can be home-made, give better service, The copper should be eut into strips 64 by 2 inches wide. A terminal from the outside zine container of an old "A" cell should be soldered on to the short side for contact with the wire and the zine of the next cell. Into the porous pot, which should be thoroughly clean, pour an ounce of mercury, which should be just sufiicient to cover the bottom of the pot with a thin veneer, and is to be used only with home-made or _ nonamalgamed zine, Place the zinc in the pot. Prepare the sulphuric acid and the water by. pouring the sulphuric acid into the water, and not vice versa, aS this may cause an accident. Fill each of the’porous pots almost to the top with this solution. Place a handful’ of bluestone in each glass container, and half fill with distilled or fresh rain water. Placé one porous pot with its zine and sulphuric acid into the bluestone solution, You now have the following :- An outer glass container with a solution of bluestone and water, a2 porous pot containing a solution of sulphuric acid, the zine and a little mercury. The cell is now complete but for the copper plate, which goes on the outside of the porous pot, that is, bluestone solution. If the glass jars are not quite full, add enough distilled water until the levels in both containers are almost the same, | The cell should be left.to stand for a

while until the ingredients are properly dissolved, and then connected, as-is shown in the diagram. The zine of one cell is connected to the copper of the other, until the required number of cells are connected. .There will be a zine and a copper left, and these will be the negative and: "positive of: :‘the charger. co Those who cannot obtain pure sulphuriec acid, should use. commercial, which, being not so pure, must be mixed to a strength of one. part to 40 by weight,- Epsom-salts: may be used instead of the sulphuric, and a haltsaturated solution is made by mixing 64 ounces of Epsom salts to a pint of water, This completes the Daniell cell, and it should function quite well, It will be found that the zincs will need to be renewed about every. six months, -that bluestone must be added every fortnight, and that perhaps after twelve months sulphuric acid will have to be renewed. If Epsom salts are used, the solution will have to be renewed fairly often. If the zines eat through too quickly it is an indication éither that they are not properly amalgamated or that they are too thin, or that the zinc is impure or that the solution in which they are immersed is too strong. If the joints begin’ to eat away through corrosion, clean them and smear them with wax, If the voltage is not up to standard, one of the solutions is weak-probably the bluestone. The solution should be saturated, i.e., the water. should have as much bluestone in it ag it will take, Watch the porous pot to see that a precipitate of copper does not form on the outside of it. This indicates a supersaturated solution, which requires thinning.