On the Viscosity of Argon as affected by Temperature. 71 



capillary is at the temperature of the room ; in a closely following set 

 the capillary is bathed in saturated steam at a temperature that can 

 be calculated from the height of the barometer. 



If the temperature were changed throughout the whole apparatus 

 from one absolute temperature to another absolute temperature 6\ 

 we could make immediate application of (4) ; the viscosities (/x, at 

 the two temperatures would be directly as the times of transpiration 



t'). The matter is not quite so simple when, as in these experiments, 

 the change of temperature takes place only in the capillary. A rise 

 of temperature in the capillary now acts in two ways. Not only does 

 it change the viscosity, but it increases the volume of gas which has to 

 pass. The ratio of volumes is 6\ 9 ; and thus 



subject to a small correction for the effect of temperature upon the 

 dimensions of the capillary. It is assumed that the temperature of 

 the reservoirs is the same in both transpirations. 



The apparatus is shown fig. 1. The gas flows to and fro between 

 the bulbs A and B, the flow from A to B only being timed. It is 

 confined by mercury, which can pass through U connections of blown 

 glass from A to C and from B to D. The bulbs B, C, D are sup- 

 ported upon their seats with a little plaster of Paris. The capillary is 

 nearly 5 feet (150 cm.) in length and is connected with the bulbs by 

 gas tubing of moderate diameter, all joints being blown. E represents 

 the jacket through which steam can be passed ; its length exceeds that 

 of the capillary by a few inches. 



In order to charge the apparatus, the first step is the exhaustion. 

 This is effected through the tap, F, with the aid of a Toppler pump, 

 and it is necessary to make a corresponding exhaustion in C and D, or 

 the mercury would Ije drawn over. To this end the rubber terminal 

 H is temporarily connected with G, while I leads to a common air 

 pump. When the exhaustion is complete, the gas to be tried is 

 admitted gradually at F, the atmosphere being allowed again to 

 exert its pressure in C and D. When the charge is sufficient, F is 

 turned off, after which G remains open to the atmosphere, and H is 

 connected to a manometer. 



When a measurement is commenced, the first step is to read the 

 temperatures of the bulbs and of the capillary; I is then connected to a 

 force pump, and pressure is applied until so much of the gas is driven 

 over that the mercury below A and in B assumes the positions shown 

 in the diagram. I is then suddenly released so that the atmospheric 

 pressure asserts itself in D, and the gas begins to flow back into B. 

 The bulb J allows the flow a short time in which to establish itself 

 before the time measurement begins as the mercury passes the 



