288 Mr. S. U. Pickering on the Hypothetical 



simpler explanation is that it had dissolved during the filtra- 

 tion and after the estimation of the evolved chlorine, especially 

 as no precautions whatever were taken to keep the liquid at 

 — 26° while being filtered, and as (according to Mr. Vernon 

 himself) the solubility of the dioxide increases rapidly with a 

 rise of temperature. Some error of unknown magnitude 

 must, at any rate, have been introduced in this way, and 

 would render the results entirely untrustworthy, yet on these 

 results, although opposed to his subsequent experiments, 

 Mr. Vernon's sole argument against the higher chloride being 

 Mn 2 Cl<5 depends. 



2. The greatest amount of available oxygen obtained by de- 

 composing the higher chloride by water is 50 per cent, of that 

 present in the dioxide taken (see equation 4). If the dioxide 

 contains any protoxide the amount recoverable will be in- 

 creased, one gram molecule increasing it to 100 per cent, 

 (equation 5). The sample used by me contained a little 

 monoxide, for the presence of which due allowance was made 

 (although Mr. Vernon concludes otherwise); and Mr. Vernon, 

 therefore, made some experiments " to see if it were not 

 possible to recover more than this (50) percentage when pure 

 dioxide was used." Unfortunately, however, he has forgotten 

 to say anything about the results of these experiments, and, 

 more unfortunately still, in those experiments with impure 

 oxides which he does quote he has forgotten to make any 

 allowance for the impurity (protoxide) which they contained. 

 Making this correction for him, his results are as follows : — 

 I. II. III. 



at~5°. at -9°. '^atlS .^ at 13°. 



514 51'0 45-4 46*1 47'6 per cent, of the dioxide 



recovered. 



The numbers scarcely warrant the conclusion that "instead 

 of the amount of dioxide recovered being always slightly 

 below fifty per cent, it is always slightly above it." It is 

 only above it in one case ; and then by such a small amount 

 that it is entirely insignificant in experiments depending on 

 the results of two rather difficult analyses, especially as Mr. 

 Vernon gives the results of but one analysis in the whole of 

 his paper, affording us, therefore, no data from which to judge 

 of the magnitude of his experimental error. It is interesting 

 to note that Mr. Vernon's results in experiment I. confirm my 

 own conclusion that a reduction of temperature below about 

 6° causes no appreciable increase in the dioxide recovered. 



Mr. Vernon having concluded that a little over, but not 

 much over, 50 per cent, may be recovered, naturally finds 



