THE VISCOSITY OF PURE LIQUIDS 585 



Substance. >) . 10 s . s. 7).io'vs. 



Carbon bisulphide . . . 305 1*222 276 



Methyl sulphide . . . 253 0*832 277 



Ethyl sulphide .... 234 0*739 272 



Benzene 316 0*809 3S° 



Thiophen 339 0*988 341 



The general result of this comparison between the viscosity- 

 coefficients and the density at the respective boiling-points — 

 that is, at the temperatures at which their vapour pressures 

 under normal atmospheric pressure are the same — of these 

 eighty-eight liquids, when we exclude the strongly associated 

 alcohols and acids, in other words hydoxylated compounds, is 

 to show that the quantity y : \/s is of the same order of magni- 

 tude. Further, in each of the natural groups the values of 

 i) : \/s are very nearly constant. This is true not only of the 

 saturated hydrocarbons and the ethers, but also for the groups 

 of esters. The tables show that the individual members of 

 each group of alkyl iodides, bromides and chlorides are found 

 to have very nearly the same value, the mean values for the 

 monohalogen compounds being respectively 278, 289, and 302. 

 Hence in these substances chlorine acts a little more strongly 

 than bromine, and bromine somewhat more strongly than 

 iodine ; that is, viscosity tends to diminish very slightly with 

 the increase in the atomic weight of the halogen. At the same 

 time it ought to be noted that all the allyl halides have the 

 same viscosity-coefficient at the boiling-point when treated 

 by Arrhenius's method, as will be seen from the following 

 table : 



>» . 10 5 . s. »j , 10 s : v«. 



Allyl iodide .... 344 1 *66i 273 



Allyl bromide . . . .315 l '33& 273 



Allyl chloride .... 262 0*9219 276 



Although even in this case chlorine appears to act a little 

 more strongly than the other halogens. 



In the case of products containing two halogen atoms, 

 methylene and ethylidene chlorides are found to have identical 

 values of rj : Ss, viz. 320 ; this is further almost identical with 

 the values for carbon dichloride and chloroform. 



