408 G Barus — Viscosity of Gases at high temperatures. 



tween viscosity and temperature of which the following little 

 table is a good exhibit. Air and hydrogen are the gases chosen. 

 In the table d", r/\ £", respectively denote the temperature, 

 the viscosity and the coefficient of external slip of the gas, 

 R" the radius of the capillary tube at d" ; and /), £, R, have 

 the corresponding signification at 0° C. The measurements 

 were made absolutely. The time of efflux (t) for a known 

 volume of gas V =50 cc nearly, varied in round numbers from 

 t=lQ0 s ™ at 0° C. to £=2350 sec at 1200° for air, and from 

 2=85 sec at 0° C. to £=900 sec at tf'^lOOO for hydrogen. R in 

 these experiments is about - 0079 cm . The capillary platinum 

 tubes were used in fascicles of two, side by side, and wound 

 together in form of a nearly compact helix, at the internal and 

 external surfaces of which temperature was measured. From 



the absolute values of in" : I 1+4-^ J, the quotients in the third 



column of the table are computed, which quotients in propor- 

 tion as £" approaches zero reduce to in" : in. "With this value I 



2 



have compared (1 -fa d")* where a=0-003665. This compari- 





0" 



ri" 









1+4?"/jR" 

 V 



DifE. 





■\/{l+ae"f 





l+4C/i? 





Air (Table XXV) 



565° 

 592 



2-083 

 2-111 



2-113 



2-158 



— •030 





— ■041 





995 



2-693 



2-185 



— •092 





1216 



3-141 



3-099 



+ •048 



Air (Table XXVIII) 



442 

 569 



1-991 

 2.149 



I -900 

 2-119 



+ •091 





+ •030 





982 



2-111 



2-166 



— •055 





1210 



3-214 



3-092 



+ ■122 



Hydrogen (Table XXVI) 



961 

 1212 



2-112 

 3-581 



2-134 

 3095 



+ •038 

 + •486* 



Hydrogen (Table XXVII) 



418 

 512 



1-935 



2-098 



1-858 

 2-023 



+ •011 

 + ■015 





520 



2-113 



2-036 



+ •011 





952 



2-160 



2-121 



+ -039 



* Platinum pervious £o hydrogen, 

 (notably the thermo-element) by direct comparison with the air-thermometer. I 

 have given the porcelain bulb a re-enfrant form, the bottom folding inward in 

 such a way as to form a narrow cylindrical tube, the closed end of which is at the 

 center of figure of the bulb. Into this central tube the junction of the thermo- 

 couple to be calibrated is inserted. To further insure identity in the environments 

 of the two pyrometers to be compared, the air thermometer bulb is snugly 

 surrounded by a spherical muffle revolving around a horizontal axis. This muffle 

 is in its turn surrounded by the walls of a nearly spherical furnace, the burners 

 of which are set something like a force-couple and blow into the furnace a cyclone 

 of flame revolving around the vertical. Chapter V concludes with a full experi- 

 mental discussion of the subject set forth in the above text. 



