79-2 



ropular Science Monthly 



liition, and a complete wiring diagram 

 for tlie entire transmitting and receiving 

 station will be given. The manipulation 

 of the apparatus, the methods of calling 

 and answering and of sending messages, 

 as well as the construction and ijst jf 

 the antenna change-over and the detec- 

 tor-])rotecting switches will he discussed. 

 The remaining instruments needed for 

 the receiver are even easier to construct 

 than the detector and condenser out- 

 lined here. It would be a good plan 

 for the experimenter to complete his 

 tr.insmilter (as described last month) 

 now and ihe apparatus shown in this 

 article, so that he will be all ready to 

 put his station into complete operation 

 soon after the appearance of the next 

 article. It should be remembered that 

 for exchange of messages between two 

 stations it will be necessary to build two 

 of each of the instruments <lescribed, so 

 that each station may be completely 

 equipped aiul thus prepared both for 

 sending and for receiving. 



A 



Caring for Storage-Batteries on 

 Automobiles 



WKAK or exhausted battery will 

 cause misfiring in an engine, be- 



Adding luw solution 

 or water to a weak stor- 

 age battery cell to test 

 the specific gravity 



cause the current voltage is not 

 sullicient to make a good hot 

 spark jump across the spark-gap. 

 A battery becomes weak, or 

 dc.id, because of some intern. il 

 difcci resulting from short-<ir- 

 1 iiiling, due to the C(jllecti(jn of 



sediment, destruction of insulation and 

 the bucklingof the plates; or, perhaps too 

 little attention is given to the recharging 

 re(|uirements which vary with the use of 

 the car. It is I)est to anahze the char- 

 acter of the driving before finding fault 

 with the lialtcry to see if a too great 

 demand has been made upon it. A 

 doctor or a city salesman, making many 

 stops, will consume more current than 

 the battery will stand, ilue to the fre- 

 (|uent cranking. Continued use of a car 

 at night will place an added burden on 

 tlie battery to light the lamjis, which, 

 may e(|ual or exceed the output of thd 

 generator going at the speed one tra\clsl 

 at night. Under these conditions a! 

 battery may be in a completeh' run^i 

 down or dischargetl condition when' 

 tested in the morning. The specific 

 gravity of the electrolyte may drop' 

 below 1,150. One of the chief causes of 

 battery exhaustion is excessive cranking. 



The h\-drometer springe is used in the 

 manner illustrated in making tests for 

 sjiecitic gravity. When rehlling the cells 

 with fresh distilled water or putting in a 

 new solution squeeze the bulb, and 

 place the rubber tip in the receptacle 

 containing the solution. The bulb is 

 then released, anil the licpiid is drawn 

 into the glass tube. Insert the tube in 

 the vent hole of the battery, and 

 squeeze the bulb lightK- to eject enough 

 (if the contents to till the cell. Release 

 tlie l)uli) aiul <|uickh- turn the tube to a 

 horizontal position, to keep the solution 

 from dropping on the upper surface of 

 the battery. Press the bulb to expel the 

 remaining li(|uid, replace the vent 

 plugs ,ind wipe the moisture and dirt 

 from the top of the cell. 



To I<>st the specific gra\il\-, dr.iw in 

 enough li(|uid to till the syringe anil hold 

 it toward a light. The floating part will 

 show the density by the graduations. 



D' 



Discarded Type-Cases in the 

 Amateur's Shop 

 klStWRDi;!) lyi)e-cases, obtainable 

 from any jirinter, can be put to 

 excellent use in the shop of the amateur 

 mechanic. Such cases may be iise<l for 

 keeping screws, nuts, bolts, washi-rs, etc., 

 w iiere I hey can be easily found. Fasten 

 Iwoor three of them under the work-bench 

 where they will bi' within easy reach. 



