Popular Science Monthly 



chloride of zinc, which is required to make 

 up the exciting mixture. In preparing 

 chloride of zinc, the scrap-zinc should be 

 placed in a large stoneware crock and 3 or 

 4 lb. of commercial hydrochloric acid 

 poured over it. This must be done out- 

 doors, because the hydrogen gas that is 

 given off is harmful to breathe, and also 

 inflammable. A great heat is generated 

 and the liquid may boil up and make it 

 run over the top of the crock. A small 

 quantity of cold water may be poured in 

 to lessen the chemical action without 

 detriment to the resulting product, which 

 should be left until quite cold before using. 

 It is very important that this solution 

 should contain no free hydrochloric acid, 

 because its introduction into the made-up 

 cell would cause chemical action, and the 

 cell would soon be destroyed. Any trace 

 of free acid is readily dispersed by adding a 

 small quantity of chloride of ammonium 

 in powder form and stirring the liquid until 

 effusing ceases. By this method a small 

 quantity of chloride of ammonium may be 

 introduced without harm. As soon as the 

 solution of chloride of zinc is ready it may 

 be strained through a piece of damp muslin 

 to free it from dirt, paper chips and other 

 matter, and then filtered through a tuft 

 of cotton pressed in the neck of a glass 

 funnel. This will free the solution of any 

 fine iron-deposit or lead that may have 

 been in the zinc, thus aiding the efficiency 

 of the re-made cell. This solution should 

 test 32 deg. Baume. Sal ammoniac, or 

 chloride of ammonium in the crystal form, 

 is then dissolved in the chloride of zinc. 

 Filtered or distilled water is then added 

 and the mixture stirred well and tested to 

 register 32 deg. Baume. The solution is 

 then ready for use. 



The carbon-rods and the brass binding- 

 posts and screws must be cleaned and the 

 zinc-cylinder lined with a double thickness 

 of blotting-paper, or blotting-board, cut so 

 as to leave a margin of about Yi in. at the 

 top where it is turned over on the outside. 

 Cut some circular pieces of cardboard, or 

 heavy blotting-board, so that they will fit 

 tightly into the interior of the blotting 

 paper. Press three or four of these down 

 into the bottom of the blotting-paper 

 lining inside of the zinc-cylinder. It is then 

 ready for filling. Just before putting in the 

 mixture pour in some of the chloride solu- 

 tion so as to wet the paper all over, drain 

 it and place the zinc upside-down to drain 

 off the excess liquid. This takes about 



149 



20 minutes, for the paper must not be over 

 wet. Then place upon a smooth board 

 about 1 34 lb. of the carbon and manganese 

 powder that has been treated. Add about 

 3 oz. of the chloride of zinc and chloride of 

 ammonium solution and mix well so that 

 it will hold together when gripped in the 

 hand. It must not be very wet or it will 

 not give the proper amperage. The right 

 consistency is very important. Pour some 

 of the carbon mixture into the paper-lined 

 zinc-cylinder and ram it down hard ; insert 

 one of the carbon rods, adjust it centrally, 

 then pack some of the mixture around it 

 and ram it down tight with a suitable strip 

 of wood, hammering it in with a wood 

 mallet. The carbon rod must be tapped 

 down occasionally to prevent it from lifting. 



The tighter the mixture is packed the 

 greater will be the amperage when finished. 



Cut off the outside edges of the blotting 

 paper and fold the top of it inwards toward 

 the carbon-rod, press it down and see that 

 none of the carbon mixture makes contact 

 between the zinc and the carbon-rod. This 

 is essential as the connection would short 

 circuit the cell. Place all the binding 

 screws in position, test the cell with a 

 suitable battery ammeter and see that the 

 screws of the carbons are tightly fitted. It 

 should give a current of 15 to 22 amperes. 



Dry the sand and pack some of it over 

 the top; then melt the tar and pour it on 

 the sand to completely fill the cell to the 

 top. These made-over cells will give an 

 excellent working current for a considerable 

 length of time. 



Method of Insulating Secondary * 'Pies*' 

 in Transformers 



IN most text-books on the construction 

 of transformers, it is customary to 

 advise the insulating of the "pies" or 

 sections in the secondary winding by means 

 of long strips of empire cloth, wound over 

 and over through the center holes of the 

 sections. This requires a good deal of 

 work on the part of the constructor. 



While overhauling a transformer, the 

 writer tried out a somewhat novel method. 

 The core was insulated in the usual manner, 

 with a number of layers of empire cloth, 

 but the "pies," instead of being wound with 

 strips of empire cloth, simply had round 

 disks of empire cloth, of double thickness, 

 between each pair of sections. This gave 

 fully as good insulation, and made access to 

 the different sections easier. 



