On the Decomposition of Equivalent Solutions of Iodides. 89 



side of the square has to be taken equal to § wave-lengths, and 

 in the second the height of the triangle as equal to § ware- 

 lengths. The two expressions for the wave-velocity become 

 f x ii x 92, and f x 1 x 152, both of which expressions are 

 equal to 33f . Hence we are perhaps justified in inferring 

 that the edges are stationary, and that the wave-velocity in 

 the soap-film is nearly 34 inches in a second. 



XIY. Laws governing the Decomposition of Equivalent Solu- 

 tions of Iodides under the Influence of Actinism. By Albert 

 E. Leeds, Ph.D.* 



IN a paper published in the Philosophical Magazine for 

 June 1879, I have given a brief review of the contro- 

 versy as to whether potassium iodide, in a very dilute solution, 

 is decomposable by sulphuric acid. I likewise pointed out, 

 that the explanation of the opposite views entertained by ex- 

 perimenters upon this question was due to their having over- 

 looked the essential part played by air or oxygen in the reac- 

 tion. This last was brought to view by Baumertf, in the 

 course of experiments by which he showed that Andrews!]:, in 

 the famous investigation undertaken to prove that Baumert's 

 hypothesis that electrolytic ozone is a teroxide of hydrogen§, 

 was false, had himself fallen into an error. For Baumert 

 showed that when a stream of electrolytic ozone has been de- 

 prived of all its active oxygen by passing through a neutral 

 solution of iodide of potassium, it may bring about a liberation 

 of iodine in an acidified solution, placed later in the series, 

 many times greater (from 4 to 10 in the experiments tried) 

 than that effected by the ozone itself in the first instance. So 

 the curious fact remains, that while Andrews's main conclusion 

 is true, all the results by which he succeeded in establishing it 

 are affected by a constant error, and are in excess of their true 

 values. The triumph of Andrews's opinion (1856) that ozone 

 contains no hydrogen whatsoever, but in its substance -matter 

 is identical with the matter of ordinary oxygen, probably ex- 

 plains why the permanently valuable part of Baumert's work 

 has generally been lost sight of, and why the erroneous me- 

 thod of titrating ozone with an acidified solution of potassium 

 iodide has been persisted in even down to the present day. 

 Ten years after the facts above stated were made known by 



* Communicated by the Author. 



t Pogg. Ann. xcix. p. 88. 



X Proc. Roy. Soc. vii. p. 475 ; Pogg. Ann. xcviii. p. 435. 



§ Phil. Mag. vi. p. 51 ; Pogg. Ann. lxxxix. p. 38. 



Phil. Mag. S. 5. Vol. 10. No. 60. Aug. 1880. H 



