GAS ENGINES 



503 



plates. The result is a weakened battery or one which is 

 entirely inactive. 



When a hydrometer test shows that the electrolyte has 

 a gravity approaching 1 . 1 5, the battery should be recharged. 

 A direct current only may be used for this purpose. In 

 storage batteries the rate at which they should be charged 

 is stamped on the manufacturer's name plate. It is usually 

 most convenient to use several ordinary incandescent lamps 

 to secure the desired amperage. The pressure may be any 

 voltage which is above the ultimate voltage of the battery. 

 It may take from twenty-four to sixty hours to bring a 

 battery up to full charge. It is exceedingly important that 

 the direction of current from the outside source be accurately 

 determined, since the current must go through the battery 

 in the direction opposite to that by which the battery 

 delivers its current. Positive of source must be connected 

 to positive of battery. If a compass is at hand, this may be 

 used as shown in Figure 395. Another determination may 

 be made by means of a little 

 of the sulphuric acid solution 

 drawn from the cell or by acid 

 secured from an outside source. 

 Into a small vessel of the acid 

 the bared terminals may be 

 immersed. The positive termi- 

 nal will show a brownish color, 

 while the negative will be „ T*°. m P*t* . 



# riG. 395. Showing the influence 



bright. A third determination upon a magnetic needle of the field 



, 1 1 . . r surrounding a conductor when the 



may be made by immersion ot nce die is brought within range. 

 the ends of the wire in a vessel *&*£»&& ££.%*£. 



Containing a Solution of COm- ductor when the current is flowing 



m-t • • as indicated by the arrows. The 



mon Salt. the bubbles rising position "B" will be taken if the 



from the terminals will be needle is held above the conductor 



oxygen from the positive and hydrogen from the negative. 

 Since there is twice as much hydrogen as oxygen in water, 

 the polarity will be determined by the excess of bubbles. 



