Hartmann & Bratin, Bockenheim- Frankfort o. M. 



165 



Apparatus 

 for measuring Temperatures by Electrical Instruments. 



20. Braun's Pyrometer for temperatures up to 1000 and up to 

 1500 C, based upon the variation of the resistance of a platinum wire 

 wound so as to obviate self-induction inside a non-combustible box and 

 forming one branch of a "Wheatstone bridge. The sensibility is so great 

 that with the highest temperatures an increase or decrease of but a few 

 degrees is rendered apparent. The absolute accuracy is extremely great, 

 the instrument being standardized by numerous comparisons with a 



porcelain air thermometer. 







The necessary manipulations are extremely simple and imply no previous 

 experience. The temperatures are directly read from a scale on the apparatus; 

 the latter may be set up at a distance of several meters from the oven. This 

 pyrometer forms therefore a most suitable controlling instrument in metallurgical 

 and ceramic operations. 



21. Tele-thermometer, similar in prin- 

 ciple to the pyrometer but limited to tempera- 

 tures between 30 and 300 C. Within these 

 limits the scale may be adjusted as required. 



The manipulation is still simpler than that 

 of the pyrometer. The telethermometer is princi- 

 pally adapted for regulating the temperature in 

 schools and public buildings from a central heating 

 station, for conservatories, or inaccessible spaces, 

 e. g. malt-kilns, drying rooms, baking ovens etc. 



Measuring Apparatus according to Kohlrausch. 



In the case placed at the right hand side of the entrance. 



22. Wheatstone - Kirchhoff Bridge. The resistance wire which 

 is 3 meters long, is wound upon a cylinder of white marble, there being 

 10 convolutions; the permanent connections are ensured by brushes; the 

 sliding contact is made by a small wheel. The comparison resistances 

 of 1, 10, 100, 1000 ohms and the resistances which are to be measured 

 are interchangeable by means of plug connections. Eminently suitable 

 for exact measurements. 



