94 ELECTROLYSIS. 



Genoa, and M. Blast, professor at Louvain, assimilating 

 dynamo-electric machines to batteries, have written that the 

 maximum capacity of a machine was attained when the external 

 resistance equalled the internal resistance. This is incorrect 

 from a really practical point of view. 



In certain conditions of speed it is, indeed, possible to get 

 the maximum of capacity to correspond to the equality of 

 resistances ; but that speed, in a well made machine, never 

 corresponds to the maximum speed which it is possible to 

 obtain. Consequently, the machine does not give all the watts 

 which it is capable of industrially giving. 



In order to demonstrate this assertion, we have undertaken 

 a series of experiments with the type of the Gramme machine 

 most generally in use and known as the normal type.* 



The normal type of Gramme machine is particularly appli- 

 cable to lighting ; but it has also been used for the construction 

 of electroplating machine type No. 2. The volts and the 

 amperes naturally vary with the sizes of wires wound round the 

 bobbins and the electro-magnets. 



We first experimented upon a machine capable of giving 

 and maintaining, without any dangerous heating, a current of 

 25 amperes, and we ran it at its practical maximum speed of 

 1750 revolutions. The internal resistance was, when cold, 

 1 '083, and, after four hours' working, 1 136 ohm. 



The work expended by mechanical friction and the driving 

 band, measured with a good dynamometer, was found to be 30 

 kilograinmetres without any sensible variation during the time 

 of the experiment. 



The external resistance varied from 2 to 12 ohms. We did 

 not attempt to go below 2 ohms, as with such a resistance a 

 current of 51 amperes was made to pass through wires which 

 could only practically convey 25. With such an exceptional 

 intensity we could only get a few minutes' continuous work at 

 a time, owing to the abnormal heat developed in the bobbin 

 and in the electro-magnets. 



* On the 1st July, 1884, the inventor had delivered to the industrial world 

 more than 4300 machines of this type. It is the electrical apparatus most 

 extensively used in the world. 



