[ 490 ] 

 LV. Intelligence and Miscellaneous Articles. 



ON THE BOILING-POINT OF OXYGEN, OF AIR, AND OF CARBONIC 

 OXIDE UNDER THE ORDINARY ATMOSPHERIC PRESSURE. BY 

 M. S. WROBLEWSKI. 



IN my Note presented to the Academy on the 31st December, 

 1883, I showed that by expanding liquid oxygen a fall of tem- 

 perature to — 186° C. is easily obtained. 8ince then I have directed 

 my attention to the methods for measuring low temperatures. 



It is clear that the use of the hydrogen thermometer, which served 

 in my researches on the liquefaction of oxygen, must have a limit. 

 It is needless to say that, as we approach the temperature at which 

 hydrogen liquefies, any calculation of temperature based upon the 

 pressure exerted by the gas becomes illusory. But there is another 

 circumstance which, in such cases, lessens the degree of certainty 

 necessary for these measurements. 



The thermometer based on the expansion of gases under a 

 constant volume consists, as we know, of a bulb immersed in the 

 medium whose temperature is to be determined, and of a narrow 

 tube connecting this bulb with the manometer. In many cases 

 the temperature of this tube cannot be accurately determined; and 

 the exactitude of the measurements is changed when the volume 

 of the tube becomes comparable to that of the bulb. This is the 

 case in experimenting with gases so difficult to liquefy as nitrogen, 

 atmospheric air, or carbonic oxide, where the thermometric bulbs 

 cannot have the necessary size. Comparing several hydrogen 

 thermometers, constructed with bulbs of different magnitudes, with 

 Jolly's air thermometer, I observed that the uncertainty of the 

 measurements increases as the bulb is smaller, and as we get away 

 from the zero of the thermometer. This uncertainty is still greater 

 when we want to determine at a given moment, by means of such 

 a thermometer, the temperature of a medium which is not in the 

 stationary state, and which becomes heated or cooled. Hence all 

 determinations of the solidifying point of liquids made with the 

 hydrogen thermometer cannot be exact. 



For the same reason I decided to base the methods for measuring 

 low temperatures on the thermo-electrical properties of metals. By 

 using aperiodic galvanometers of great resistance and great sensi- 

 tiveness, it is easy to measure the electromotive forces due to 

 differences of temperature. It is sufficient then to compare the 

 indications of such an apparatus with those of a hydrogen ther- 

 mometer of large size, and at constant temperature, to have a 

 certain and sufficiently delicate method of determining any change 

 of temperature, even when very sudden and of short duration. 

 In order to give an idea of the delicacy of the method, I may say 

 that, working at temperatures of about —200° C, I can measure 

 ttjoVtrt °^ a von % which represents a change of temperature of £ 

 of a degree. 



Thanks to this method I have been able to measure the boiling- 



