DYNAMO-ELECTRIC MACHINES. 



83 



magnets and to produce the chemical work for which they are 

 intended. 



The Weston machine is provided with a rotary governor 

 fixed on the bed-plate and receiving its motion from the spindle 

 of the dynamo. The object of this governor is to automatically 

 shunt the circuit through a resistance when the surface of the 

 pieces in the bath becomes too small. 



All the makers of electrical apparatuses also employ shunts 

 and resistances for equilibrating the external resistance and 

 preventing the pieces from being damaged by the action of too 

 dense a current, but they prefer to regulate these appliances by 

 hand instead of automatically. 



The electro-magnets of the Weston machine are provided 

 with steel plates; this arrangement prevents the change of 

 direction of the current when the counter electromotive force 

 becomes too great. 



We are indebted for the following particulars of the Weston 

 machines to Messrs. Hanson, Van Winkle and Co., the pro- 

 prietors of the patents in the United States. 



TARIFF OF WESTON MACHINES FOR ELECTROPLATING. 



The amount of horse-power can easily be translated into 

 watts if we want to compare the price of these machines with 

 those of other systems. The 40 centimetre machine, for in- 

 stance, can be considered as having an efficiency of 70 per 100 ; 

 with 300 kilogrammetres it therefore produces 2100 watts ; its 

 price being 4000 francs, the watt costs about 2 francs. 



A Gramme machine of a value of 2000 francs gives prac- 

 tically 300 amperes and 15 volts, that is to say, 4500 watts, 

 which puts the cost of the watt at 45 centimes. 



A Schuckert machine of 415 kilogrammetres costs 2150 



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