of Gases and Molecular Force. 523 



only (to be denoted by H) at any temperature can be calcu- 

 lated by the formula (4) above, where the symbol H is repre- 

 sented by 7]. 



In the following table t denotes temperature 0. and 77 is 

 the viscosity of the vapour found by experiment at that tem- 

 per ature, while H is the part of the viscosity calculated as 

 due to collisions, and then the difference between the two 

 expressed as percentage of the calculated numbers is denoted 

 by diff. %• 



(0 a H 5 ) a O. 



e » 



t 7-2 10 155 18-9 25-8 31-4 365 



n 71-2 71-6 732 735 755 771 793 



H 65-5 662 677 686 703 71-9 73-3 



Diff.°/ . 9 8 8 7 7 7 8 



C 2 H 5 C1. 



, * N C 6 H 6 . (CH 3 ).,CO. CHCI3. 



t 16-4 53-5 157 17 17" 17 



n • 94-1 105-8 144-0 76 78 103 



H 81-7 93-8 126-7 66-2 71 92 



Diff.°/ 15 13 14 15 10 12 



Methyl formate. 



CS 2 H 2 0. 2 H 5 0H. , « N 



t 17 17 17 20 100 



tj 99 97 88-5 923 135-2 



H 90 109 98-2 90-8 119-0 



Diff.°/ 10 -11 -10 2 13 



Propyl acetate. Methyl isobutyrate. 



t 15~~ 77-8 100^ 24 65-5 100^ 



n 74-3 95-4 109-6 75-4 99-9 112-2 



H 620 77-8 83-6 64-3 74-5 83-6 



Diff. °/ 20 23 31 17 34 34 



The comparison, except in the case of water and alcohol, 

 establishes the theoretical provision that the viscosity of a 

 vapour is greater than that due to the collisions of its molecules, 

 and water and alcohol have been proved to be exceptional as 

 regards molecular force, both as vapours and liquids, so that 

 we have no right to expect them to be otherwise than ex- 

 ceptional here ; indeed, we see here another opening towards 

 the elucidation of the exceptional nature of these substances. 



Excepting the esters, we can say that at ordinary tempera- 

 tures the part of viscosity due to deflexion of paths by mole- 

 cular attraction without collision is between 8 and 16 per 



