GAS ENGINES 



501 



0^©^0^0\ 



Pig. 391. 



Series method of connecting 

 dry or storage cells 



Fig. 392. Parallel connection of cells 



open-flame, hot-bulb, and hot-tube. Later developments 



are high compression and electric-spark. Of these the 



electric-spark ignition only will be discussed, as it is used 



in all small stationary 



and portable engines, 



motor vehicles, and 



tractors. There are two 



types of the electric 



system, the make-and- 



break and the jump 



spark. The source of 



current in either system 



may be: primary cells 



(wet or dry) ; secondary cells (storage cells) ; or generators, 



low-voltage, direct or alternating current, or high-voltage, 



alternating current. 



Source of current. Primary cells. Primary cells used 

 for ignition may be of either the wet or dry type; but the 

 former are not extensively used because the electrolyte may 

 be spilled and the jars or containers broken. The voltage 

 of a dry cell (Fig. 390) is 1 to 1 . 5, and the amperage should 

 be 25 to 30. A dry cell which shows above 30 amperes is 

 generally very short-lived. The chemical action is so rapid 

 that the zinc of the cell is quickly destroyed. Better service 



may be had from 

 cells testing 

 about 2 5 amperes 

 than from those 

 testing 30. When 

 a number of cells 

 are connected in 

 series (Fig. 391), 

 the voltage is the 

 sum of the voltages of the several cells ; when connected in 

 parallel (Fig. 392) , the resulting current has the voltage of one 

 cell and the amperage of the sum of the cells. A combination 



Fig. 393. Multiple series method of connecting cells 



