

AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XIX. — A Universal Switch for Thermoelement Work 

 and Other Potential Measurements ; by Walter P. White. 



The switch here described is used to simplify the manipula- 

 tions required in making simultaneous measurements with dif- 

 ferent electrical instruments, especially thermoelements or 

 other sources of electromotive force. The type is more effec- 

 tive, thermoelectrically, than any other known to me, is more 

 convenient to manipulate, is easier to take apart, inspect, or 

 clean, and has a distinctive advantage in the ease with which 

 it can be constructed. Similar switches have been used in our 

 laboratory for the following purposes, among others : (1) In 

 melting point determinations, to measure the temperature at 

 one or two points in the furnace cavity as well as in the charge, 

 thus permitting a better regulation of the furnace temperature, 

 an allowance for its fluctuations, and a closer estimate of the 

 thermal magnitudes involved ;* (2) in work on heat conduc- 

 tion, to avoid certain errors by measuring the temperature at 

 several points instead of one, and to measure both gradient 

 and temperature rate without elaborate duplication of appa- 

 ratus ; (3) in calorimetry, to measure, besides the calorimeter 

 temperature itself, various temperature differences, upon which 

 the corrections depend, or which, though ordinarily not neces- 

 sary, and hence not likely to be observed unless observing is 

 easy, may be of the highest diagnostic value if unexpected 

 errors appear ; (4) in specific heat work, to make measure- 

 ments upon both furnace and calorimeter; (5) in some other 

 kinds of determinations, to measure electrical energy along 

 with the calorimetric temperatures ; (.6) in calibrations and 

 comparisons of many sorts, whether, of thermoelements, resist- 



*Cf. Melting Point Methods at High Temperatures, Walter P. White, this 

 Journal, xxviii, 478, 482-88, 1909; Zs. anorg. Chem., lxix, 337, 342-50, 1911. 



Am. Jour. Sci. — Fourth Series, Vol. XLI, No. 244. — April, 1916. 

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