28 BULLETIN OF THE LABORATORIES 



bacteria, the botanist may stimulate plant growth by it, the 

 physiologist has numerous uses for it. Then we all need elec- 

 tricity itself; the neurologist traces nerves by means of it, the 

 chemist finds every few days a new method of analysis by elec- 

 trolysis that he must needs try, the electrical furnace is rapidly 

 opening new possibilities both to him and to the mineralogist, 

 and the physicist demands it in many forms and quantities. 

 How can we get it ? Cheaply if possible ; conveniently any way, 

 for we live in a hurry. 



The primary battery, the earliest generator of current elec- 

 tricity discovered, still holds its place as the most convenient 

 source of electricity for many laboratory uses. The old Grove 

 and Bunsen batteries have never been excelled by newer forms 

 in the combination of two good qualities difficult to obtain in a 

 primary battery, viz : high and uniform electro-motive force 

 and low internal resistance. But they cannot be said to be con- 

 venient, for they must be set up anew every time they are used 

 and the chemicals employed in them are expensive and disagree- 

 able to handle. For such reasons these otherwise excellent 

 batteries have a very limited field of usefulness in the laboratory. 



For the occasional supply of a current of limited amount 

 the many forms of Leclanche battery and some of the so-called 

 dry batteries — such as are commonly used for electric bells — are 

 very convenient. The convenience lies in the fact that when once 

 set up, they require no attention, with moderate use, for six 

 months or more, as there is no waste of materials when not in 

 use. They are not commonly used for. strictly laboratory 

 purposes except in electrical testing, yet we have found them 

 generally useful when used in connection with a simple device 

 for adapting the voltage and resistance of the battery to the 

 work to be done by it. Battery cells are usually so made that 

 it is inconvenient to change their arrangement. Hence they 

 are connected permanently and used for different purposes, 

 although much better results can often be obtained by an ar- 

 rangement specially suited to the w^ork in hand. 



