1886.] Conduction and Molecular Composition, fyc. 



275 



Cl 2 than there is in bromine to form aggregates more complex tljan 

 those of the formula Br 2 . It is, therefore, not unlikely that the 

 chlorine in HC1 has more " residual affinity " than the bromine in 

 HBr,* and if so the aqueous solution of the former would have a lower 

 initial conductivity than one of equivalent strength of hydrogen 

 bromide, and the maximum would be obtained only on greater dilu- 

 tion ; which is precisely the case. 



The evidence afforded by the oxy-acids derived from the halogens 

 appears to me to be equally striking. The following are Ostwald's 

 numbers, including those for nitric acid. 



Table II. 



V. 



Xitric 

 acid. 



Chloric 

 acid. 



Per- 

 chloric 

 acid. 



Brornic 

 acid. 



Iodic 

 acid. 



Periodic 

 acid. 



2 



77-9 



77-9 



79 1 





42-57 





4 



80-4 



80-2 



82-2 





50-56 



23 71 



8 



82-8 



82 3 



84-6 





59-00 



30 59 



16 



84'9 



84-0 



86-2 





66 -3 



39-49 



32 



86-3 



85 3 



88 -1 



79-4 



72-3 



49 -23 



64 



87-4 



86-4 



89-2 



81-7 



76 -9 



59-48 



128 



88-2 



87-9 



89-7 



84-1 



80 2 



69-06 



256 



88 -4 



88-7 



89 -9 



86-1 



81-8 



76-70 



512 



88-8 



88-7 



89-8 



87 -4 



83-0 



82 -59 



1024 



88-9 



88-6 



89-8 



88-4 



83 1 



85 -38 



2048 



88-2 



87-3 



89-3 



89-0 



82-9 



87 -95 



4096 



86-6 



85-7 



87-8 



88-8 



81-8 



86-62 



It will be observed that nitric, chloric and perchloric acids differ 

 but little ; that bromic acid has a considerably lower initial conduc- 

 tivity, and does not attain the maximum so soon ; that iodic acid 

 differs still more ; and that the behaviour of periodic acid is 



* On other grounds also there is reason to believe that hydrogen chloride differs 

 more from hydrogen bromide or iodide than either of these differs from the other : 

 thus less heat is developed on dissolving hydrogen chloride in water than on disso- 

 lution of equivalent quantities of the bromide or iodide, the numbers given by 

 Thomsen being — 



HC1, 400H 2 O = 17,300 units. 

 HBr, 400H 2 O = 19,200 „ 

 HI, 400H 2 O = 19,200 „ 



The solution of hydrogen chloride which distils unchanged at 112° at the ordinary 

 pressure has approximately the composition represented by the formula H01"8H 2 < > ; 

 whereas the corresponding solutions of hydrogen bromide and iodide boil at 125° 

 and 127°, and their composition is approximately represented by the formula? 

 HBr - 5H 2 and HI-5-5H 2 0. A solution of hydrogen fluoride approximately of the 

 composition HF-2H 2 distils unchanged at 120°. 



