Chemistry and Physics. 



155 



The following table contains the details of the observations 

 made with the silver soldered German-silver platinum couple, the 

 recorded readings of the galvanometer being the means of several 

 observed readings, corrected when necessary for resistance intro- 

 duced into the circuit : — 



No. 



of 



expt. 



Substances used for 



difference 



of temperature. 



Water of 15° and ice 

 Boiling carbonic acid 



and ethylene 



Boiling ethylene at 



10 mm and oxygen _. 

 Boiling oxygen and 



nitrogen 



Boiling nitrogen and 



melting nitrogen.. 

 Boiling hydrogen and 



melting nitrogen. _ 

 Boiling hydrogen and 



melting hydrogen _ 

 Boiling hydrogen — 



solid hydrogen 



about 20 mm 



Corresponding 



absolute 

 temperatures. 



280°, 273° 

 195, 170 

 1231, 90^ 

 90|, 77£ 

 77£, 62| 

 62£, 20i 

 20i ? 



201, ? 



Mean 

 absolute 

 temper- 

 ature. 



Mean 

 galvano- 

 meter 

 reading. 



280|° 



463-2 



182-j 



693-5 



107 



724-0 



84 



279-0 



70 



320-7 



41| 



623-5 



9 



51-0 



? 



64-0 



dE/dt. 



30 

 27 

 21 

 21 

 21 

 14 

 9 



•88 

 •74 

 •94 

 •46 

 •38 

 •84 



where d Ejdt is the quotient of the mean galvanometer reading 

 by the difference of the temperatures in the third column. 



On plotting the first six of these results the 1st, 2d, and 6th 

 and means of the other three, viz., dE/dt = 21-59 at t =. 87°, lie 

 nearly on a continuous curve. The continuity of the curve, with- 

 out any approach to abrupt change of form, even in the region of 

 liquid hydrogen, shows that a silver-soldered German-silver plat- 

 inum couple is an efficient instrument for the determination of 

 the lowest temperatures hitherto reached." 



A detailed discussion of the four sets of observations, Nos. 3, 

 4, 5, 6, follows, with the results given below ; those from Nos. 5 

 and 6 are probably the most accurate. 



"The general results with the German-silver platinum junction 

 may be summarized in the following table, the typical equation 

 being dE/dt = m + nT. 



Source of constants. m 



(3) and (6) 12-52 



(4) and (6) 11-49 



(5) and (6) 9-931 



Graphically 10-2 



Mean 



n 



Melting point 

 of hydrogen. 



Solid hydrogen 

 exhausted. 



0-108 



16°-4 



15°-27 



0-158 



15°-9 



14°-7 



0-231 



15°-0 



13°'5 



0-167 



]5°-5 



14°-15 



15°-7 



14°-4 



