312 



Popular Science Monthly 



negative Lledrode 



f Positive 

 Electrodes 



Tig. 3 



Grouping of positive 

 and negative plates 



terminal, at which the current emerges 

 after passing through all the negative 

 plates, during charging, and at which the 

 current enters, on its return path on dis- 

 charge, is called the cathode. 



The conditions in operating a storage 

 cell are most exacting, and serious com- 

 plications are liable to follow violation of 

 the rules. Thus, 

 it must neither be 

 charged nor dis- 

 charged too 

 quickly, there 

 being safe average 

 rates in both cases. 

 It should never be 

 over-charged or 

 over-d ischarged 

 beyond the safe 

 limits prescribed. 

 The voltage at 

 full charge should 

 not exceed 2.6 

 volts, and its 

 working pressure 

 not more than 2 

 volts. On nor- 

 mal discharge, it 

 should not be per- 

 mitted to fall below 1.75 volts. The dis- 

 charge capacity of a storage cell (its cur- 

 rent rate) is measured in ampere-hours, 

 which are found by multiplying the current 

 in amperes by the number of hours at 

 which it can flow at not less than 1.75 

 volts. In order, however, to standardize, 

 the normal discharge rate is assumed to 

 be at 8 hours. In the main, the ampere- 

 hour capacity decreases with increase in 

 the current rate. 



The ideal storage battery or accumula- 

 tor is an electrolytic cell in which elec- 

 trical energy may be stored as chemical 

 energy until ready for use. It must be 

 capable of returning at any time all, or 

 any part, of the electrical energy put into 

 it; and when discharged, the cell must be 

 in its original condition. It is, therefore, 

 necessary to find a perfectly reversible 

 chemical reaction whose direction and 

 energy relation is perfectly controlled by 

 the electric current. That is, no chemi- 

 cal action should take place except that 

 which necessarily accompanies the flow of 

 useful current when on charge or dis- 

 charge ; and secondly, the quantity of 

 material whose chemical composition is 



changed should be proportional to the 

 quantity of electrical energy passed 

 through the cell. 



The nearness of the plates to each other 

 and the large surface obtained by using a 

 number of plates, cause the resistance of 

 the cell to be very small. The greater the 

 number and size of the plates in a cell, the 

 larger the current that can be sent 

 through it without injury to the cell. 



The. commercial importance of such 

 storage cells is due in part to their ex- 

 tremely small resistance, and to the fact 

 that they can be renewed not by means of 

 costly chemicals, but by a current ob- 

 tained from a dynamo, driven by engine or 

 water-power. 



Making a Wet Battery from Ordi- 

 nary Dry Cells 



WHEN a dry battery of an electric 

 door became exhausted and there 

 was no sal ammoniac on hand to renew 

 it, it was decided to try in its stead some 

 hyposulphate soda. After removing the 

 cardboard wrappers from the cells, a 

 number of perforations were made in the 

 zinc casing, then the cells were placed 

 into wide-mouthed fruit jars, into each 

 of which was put several spoonfuls of the 

 salt and enough water to 1^11 them within 

 1 in. of the top. If the water should 

 cover the cells, it will cause a short circuit. 

 Upon testing the battery, while the 

 cells were still in the jars, it was discov- 

 ered to be fully as powerful as one com- 

 posed of new dry cells. Then the ex- 

 periment was tried of using it just as 

 it was — a new type of wet battery. It 

 has proved so effective that after a year 

 of use it has required no other attention 

 than that of replacing the water evapo- 

 rated. Thus, at no expense, excellent 

 results have been obtained, and the cost of 

 several dry cells saved. — F. M. Wagner. 



Coating a Tin Oil Can to Prevent 

 Rust 



A COMMON tin oil can may be made 

 rust proof if it is given a coat or two 

 of paint, especially on the bottom. It is 

 worth while, occasionally when through 

 painting, to wipe oflf the paint brush on the 

 bottom of the old oil can, just before the 

 brush is laid away. — James M. Kane. 



