Tetrachloride of Manganese. ' 287 



hours. Thus my above-stated conclusion is confirmed, nor 

 does Mr. Vernon attempt to investigate the question further 

 by obtaining sufficient details for determining whether the 

 rates of evolution at different points may be represented by a 

 uniform curve or not : it is only in the experiment last 

 referred to that he gives any details at all, and those given 

 here are altogether insufficient for the purpose — only 3 values 

 for the rates. 



• Experiments II. and III., pp. 473, 474, were determinations 

 of the amount of chlorine carried away in two hours by a 

 current of air when the liquid was kept at — 14°, — 6°, and 



— 26° respectively. At the lowest of these temperatures 1*8 

 per cent, only of the available chlorine was removed, and the 

 smallness of this amount shows " conclusively/' according to 

 Mr. Vernon, " that when manganese dioxide dissolves in 

 hydrochloric acid, manganese tetrachloride and no free chlorine 

 are originally formed." As this conclusion, however, is 

 directly opposed to that which Mr. Vernon is obliged to draw 

 from some subsequent experiments, there must be some error 

 either in the present or in these subsequent experiments. The 

 present ones are, no doubt, at fault. We learn from Mr. 

 Vernon that even at the highest of these three temperatures, 



— 6°, and after the current of air had been bubbled through 

 the liquid for two hours, a considerable portion of the man- 

 ganese dioxide was still undissolved, and had to be separated 

 by filtration through a filter-paper and estimated ; pre- 

 sumably this was done in the experiment at —26° also. Now 

 Mr. Vernon's original paper, when read before the Chemical 

 Society, contained an account of an experiment precisely 

 similar to the one at —26° here given, except that in it the 

 precaution of estimating the undissolved dioxide was not 

 taken, and the chlorine removed was then found to be only 

 0*35 per cent, of the total which might have been obtained, 

 whereas here it is 1*8 per cent, of the total obtainable from 

 that portion which was dissolved, so that less than J of the 

 dioxide taken had been dissolved : presumably again (for Mr. 

 Vernon is very chary of details) about 3 grams of an oxide 

 having the composition given on p. 473 were taken, and if 

 this be so, a simple calculation will show that the observed 

 1*8 per cent, of chlorine would become converted into 50 per 

 cent, (the value which we ought to get if the higher chloride 

 were Mn 2 Cl 6 , see equation 4) if only '027 gram of the 

 dioxide had got into the filtrate accidentally. The filtration 

 of a strongly acid liquid through filter-paper is often not 

 very satisfactory, and this small amount might easily have 

 passed through unsuspected in the dark liquid, but a still 



X2 



