452 



Mr. W. Crookes. 



[Feb. 17, 



observations. At first the curve seems to follow the same direction 

 as the air curve. But at a pressure of about 620 millims. it slopes 

 more rapidly till the pressure is reduced to about 50 millims., when 

 the curve again takes the direction of the air curve. The total dimi- 

 nution between 760 millims. and 1 millim. is nearly double that of air. 



The proportion between the viscosity of carbonic anhydride and air 

 at 760 millims. is 0"9208. 



Viscosity of Carbonic Oxide. 



The results with this gas are remarkable as showing an almost 

 complete identity with those of nitrogen both in position and shape. 

 The viscosity at 760 millims. is in each case 0*1092. 



Like that of nitrogen, the curve of carbonic oxide is seen to be ver- 

 tical, i.e., assuming the curve to represent the viscosity, the gas obeys 

 Maxwell's law, at pressures between' 90 millims. and 3 millims. The 

 straight portion in nitrogen is at a little higher pressure, — between 

 100 millims. and 6 millims. 



The curve of repulsion resulting from radiation is lower in carbonic 

 oxide than in any other gas examined, and, unlike the other gases, 

 there is no sudden rise to a maximum at about 40 M. At lower ex- 

 haustions the curve is, however, higher than it is in nitrogen. 



Viscosity of Hydrogen. 



It has been found that hydrogen has much less viscosity than any 

 other gas ; the fact of the log decrement not decreasing by additional 

 attempts at purification is the test of its being free from admixture. 

 This method of ascertaining the purity of the gas, by the uniformity 

 of its viscosity coefficient at 760 millims., is more accurate than collect- 

 ing samples and analysing them eudiometrically. 



Several series of observations in hydrogen have been taken. For a 

 long time it was considered that hydrogen, like other gases, showed 

 the same slight departure from Maxwell's law of viscosity being inde- 

 pendent of density that appeared to be indicated with other gases ; for 

 the log decrement persistently diminished as the exhaustion increased, 

 even at such moderate pressures as could be measured by the baro- 

 meter gauge. Had it not been that the rate of decrease was not 

 uniform in the different series of observations, it might have been con- 

 sidered that this variation from Maxwell's law was due to some in- 

 herent property of all gases. After working at the subject for more 

 than a year, it was discovered that the discrepancy arose from a trace 

 of water obstinately held by the hydrogen. Since discovering this 

 property, extra precautions (already described at the commencement 

 of this paper) have been taken to dry all gases before entering the 

 apparatus. 



