162 Hartmann & Braun, Bockenheim- Frankfort o. M. 



7. Apparatus for determining the resistances of electrolytes 

 according to Kohlrausch, consisting of a KirchhofiMYheatstone bridge, 

 cylindrical form, an induction apparatus for generating alternating 

 currents, an unifilar suspension electro-dynamometer, a telephone, three 

 U-tubes with platinum electrodes and Arrhenius' resistance vessel. 



8. Photometric apparatus, consisting of a large precision photo- 

 meter with Lummer-Brodhun's comparison prism, standard amylacetate 

 lamp, universal incandescent lamp stand, revolving mirror for determining 

 the illuminating power of arc lights at various angles of emission, volt- 

 meter and wattmeter for measuring E. M. F's and energy expended in 

 incandescent lamps. 



By means of an intransparent curtain a dark room can be expeditiously 

 improvised. 



Small Appliances. 



9. Resistance Bridge for determining the resistances of solid 

 conductors, e. g. iusulated wire wound on a bobbin, with aperiodieal 

 needle galvanometer. Eange from 0.1 to 10000 ohms, reading directly 

 without calculation. 



10. Small universal resistance bridge-, according to Kohlrausch, 

 for determining resistances of solid conductors and electrolytes, e. g. the 

 internal resistance of cells by means of alternating currents, generated 

 by means of an induction coil supplied with the apparatus. A telephone 

 is used for measuring in place of the galvanometer. Range from 0.01 

 to 1000 ohms, direct reading. 



The two preceding appliances are specially adapted for workshop use. 



11. Wheatstone-Kirchhoff Bridge with measuring wire of 1 meter 

 length, which may be extended for very accurate measurements by 

 additional stretched wire resistances. The meter wire is calibrated by 

 means of a second contact slider, which renders the apparatus also 

 available as a Thomson double bridge. Precision resistance box or single 

 standard resistance coils serve as comparison resistances. 



12. Differential Galvanometer with index for comparing any 

 resistances; the latter will be found among the exhibits in the shape of 

 a decade crank resistance box and a series plug resistance box. 



