on the Passage of Air through Capillary Tubes. 435 



fact that the volume of a given mass of air is directly as its 

 absolute temperature, that the time required for the passage of 

 a given quantity of air through a given tube at a given pres- 

 sure should vary as T 2 . 



More anomalous are the results that the velocity does not 

 exactly follow the simple law that the rates of passage at a 

 given temperature are in proportion to the difference of pres- 

 sures at the ends, but that the time of passage of a given mass 

 of air is shortened by increased pressure in a somewhat greater 

 proportion than the increase of pressure. The deviation from 

 the law of inverse proportion is only slight, and obviously 

 belongs to a term having a small absolute factor. But an in- 

 spection of the results will show that its existence is unmis- 

 takable. 



To examine the effect of simply raising the temperature, 

 the following experiments were made : — 



(1) The current was heated in a wide tube before reaching 

 the capillary tube, being afterwards cooled again to the tem- 

 perature of the outer air. Result : — the time of passage of a 

 given mass of air was slightly increased. 



(2) The current was heated after passing the capillary tube. 

 Result : — a slight decrease in the time of passage of a given 

 volume. The decrease was only such as might be accounted 

 for from the fact that the air was not completely cooled again. 



(3) The heating and cooling of the current in the capillary 

 tube. Result : — an increase of time apparently proportional 

 to the length of the tube heated. 



The following are the experiments : — 



(1) Whole current at atmospheric temperature 22° C. 



r a \ £—050// 



(b) *=656" Mean657"-5. 



The current was then heated to 100° C. in a wide tube before 

 entering the same capillary tube. 



(a) *=670" 



(b) £=668" Mean 669". 



The slight increase of time here indicated was probably due 

 to the fact that the air current had not altogether regained its 

 normal temperature before reaching the capillary tube. 



(2) Whole current at atmospheric temperature 21° C. 



(a) *=157" 



(b) * = 156" Mean 156"-5. 



The current was then heated to 100° C. in a wide tube after 

 passing through the capillary. 

 (a) £ = 153" 



£ = 155" Mean 154"-0. 

 2F2 



