On the Viscosity of Hydrogen as affected by Moisture, 115 



gives the actual arcs of vibration, the fourth their (common) loga- 

 rithms, and the fifth the differences of these, which should be con- 

 stant. The mean logarithmic decrement can be obtained from the 

 first and last arcs only, but the intermediate values are useful 

 as a check. The time of (complete) vibration was determined 

 occasionally. It was constant, whether hydrogen or air occupied 

 the chamber, at 26' 2 seconds. 



The observations extended themselves over two months, and it 

 would be tedious to give the results in any detail. One of the 

 points to which I attached importance was a comparison between 

 hydrogeu as it issued from the generator without any desiccation 

 whatever and hydrogen carefully dried by passage through a long 

 tube packed with phosphoric anhydride. The difference proved 

 itself to be comparatively trifling. For the wet hydrogen there were 

 obtained on May 10, 11, such log. decs, as 0*0594, 0*0590, 0*0591, or 

 as a mean 0*0592. The dried hydrogen, on the other hand, gave 

 0*0588, 0*0586, 0*0584, 0*0590 on various repetitions with renewed 

 supplies of gas, or as a mean 0*0587, about 1 per cent, smaller than 

 for the wet hydrogen. It appeared that the dry hydrogen might 

 stand for several days in the viscosity chamber without alteration of 

 logarithmic decrement. It should be mentioned that the apparatus 

 was set up underground, and that the changes of temperature were 

 usually small enough to be disregarded. 



In the next experiments the phosphoric tube was replaced by 

 others containing sulphur (with the view of removing mercury 

 vapour) and solid soda. Numbers were obtained on different days 

 such as 0*0591, 0*0586, 0*0588, 0*0587, mean 0*0588, showing that 

 the desiccation by soda was practically as efficient as that by phos- 

 phoric anhydride. 



At this stage the apparatus was rearranged. As shown by 

 observations upon air (at 10 cm. residual pressure), the logarithmic 

 decrements were increased, probably owing to a slight displacement 

 of the mirror relatively to the containing walls of the chamber. The 

 sulphur and soda tubes were retained, but with the addition of one 

 of hard glass containing turnings of magnesium. Before the mag- 

 nesium was heated the mean number for hydrogen (always at atmo- 

 spheric pressure) was 0*0600. The heating of the magnesium to 

 redness, which it was supposed might remove residual water, had the 

 effect of increasing the viscosity of the gas, especially at first.* 

 After a few operations the logarithmic decrement from gas which 

 had passed over the hot magnesium seemed to settle itself at 0*0606. 

 When the magnesium was allowed to remain cold, fresh fillings gave 

 again 0*0602, 0*0601, 0*0598, mean 0*0600. Dried air at 10 cm. 



* The glass was somewhat attacked, and it is supposed that silicon compounds 

 may have contaminated the hydrogen. 



VOL. LXJI. K 



