276 Prof. H. E. Armstrong. Electrolytic [Mar. 25, 



altogether peculiar — being that of a polybasic acid, it may be added. 

 Ostwald regards it as most surprising — " in hohem Grade befremdlich " 

 — that periodic acid should be much weaker than iodic acid, and that 

 the latter should be considerably inferior to iodhydric acid. To ray 

 mind, their behaviour is absolutely what might be expected of these 

 acids. Although the molecules in liquid nitric, chloric and perchloric 

 acids are probably not of the simple composition represented by the 

 formulae HN0 3 , HCIO 3 , and HCIO4 respectively, the chemical be- 

 haviour of these acids does not indicate any; great difference between 

 them ; owing, however, to the accumulation of oxygen atoms, per- 

 chloric acid may be expected to exercise a somewhat greater influence 

 than chloric acid, as it actually does. Chemists are agreed that 

 bromine has less affinity for oxygen than chlorine ; hence it may be 

 inferred that the oxygen in bromic acid would have greater residual 

 affinity than the oxygen in chloric acid, and that, therefore, bromic 

 acid would form complex aggregates more readily than chloric acid, 

 and consequently have less influence in electrolysis than chloric acid. 

 This is true in a much greater degree of iodic, and still more of 

 periodic acid :* it is well known that the former not only yields salts 

 of the type M'I0 3 , but also acid salts such as KHI 2 6 ; and that 

 periodic acid forms a series of very complex salts. 



The acids of phosphorus form another interesting series : — 



Table III. 



V. 



H 3 P0 2 . 



H3PO3. 



H3PO4. 



2 



30-89 



28-63 



14-22 



4 



37'91 



34-29 



17-00 



8 



45-81 



41-14 



21-26 



16 



54 13 



49-09 



27-09 



32 



62-10 



56-96 



34 -41 



64 



69-06 



64-52 



43-05 



128 



74-05 



70-21 



53 11 



256 



77-84 



74-54 



Hl-8 



512 



79-92 



77-57 



69-9 



1024 



81-00 



79 11 



75-4 



2048 



81-39 



79-75 



79-0 



4096 



80-48 



79-07 



79-8 



These numbers afford to my mind the clearest possible evidence 

 that we are dealing with complex molecules. It is especially note- 



* The existence of a stable oxide of the formula I^O^ as well as thermochemical 

 data, have been interpreted as evidence that iodine has a greater affinity for oxygen 

 than even chlorine. I am inclined to take the contrary view, however, and to regard 

 the stability of the oxide I 2 5 as due less to the high affinity of iodine for oxygen 

 than to its low affinity for itself and the high affinity of oxygen for oxygen. 



