

852 



of all for liquified gases. The oscillation-method appears thus a 

 particularly suitable one for liquid gases '). 



13. With a view to our experiments it appeared to us desirable 

 to luive a rou.^h idea as to the value of the viscosity for liquid hydrogen, 

 say at the boiling point; an estimate may be obtained by the appli- 

 cation of the law of corresponding states. KAiMERi^iNGH Onnes^) has 

 shown that for two different substances obeying this law the expres- 

 sions 



must have the same value at corresponding temperatures, where 

 Tk and /;/, are the critical temperature and pressure and M the 

 molecular weigiit. It is therefore possible by the application of this 

 rule, which will be at least approximately valid, to calculate v for 

 hydrogen by comparison with a substance wiiose viscosity is known 

 over a somewhat wide range of temperatures, such as methyl-chloride 

 according to measurements by dk Haas'). For methyl-chloride 7'i=416, 



;//, = 66 (atm.), .17 = 50, and therefore 1/ —., = 0.024; for hy- 



drogen similarly 7).=31, />i.==ll, .!ƒ= 2, so that |/ —— = 0,40. 



The boiling point of hydrogen is 20^ K. and the corresponding tempe- 



416 



rature for methyl chloride is 20 "--^ = 268° K., or about 0°C., at 



■^ 31 



which temperature ij for methyl chloride is 0,0022 ; it follows tiiat for 



hydrogen at 20° K. 0,40 r, = 0,024 . 0,0022, which gives 7^ = 0,00013. 



As at this temperature the density of liquid hydrogen is about 



0,071 ^j, we have - = 0,0018. 

 f« 



') On the other hand, in Zemplen's experiments (Ann. d. Phys., 19, 783,1906) 

 on the viscosity of air in which concentric spheres were used of 5 and 6 cms. 

 radius the condition of nearly complete damping of the reflected wave is not 

 satiïfied by a long way; with .=0,0002, ju = 0,00012 and 7 = 30, &' = 0,8 i.e. 

 e—'iiiili'—U\—x about. The damping is thus so weak in this case that the tirst 

 correction-term (31) is not sufficient: we have therefore been obliged to abandon 

 our intention originally formed, of recalculating Zemplen's experiments by means 

 of our lormulae. 



^) Gomm. phys. Lab. Leiden, n". 12, p. 9. 



*) Gomm. phys. Lab. Leiden, n''. 12, p. 1 



■*) Gomm. phys. Lab. Leiden, n". I'ild. 



