482 Mr. H. M. Vernon 



on 



except in the tetrachloride solution; but as the nearest approach 

 to this, the action of chlorine gas upon it when mixed with 

 cobalt sesquichloride in a hydrochloric acid solution, was tried, 

 and also the action of lead tetrachloride in the acid solution. 

 No darkening in the colour of the solution took place, how- 

 ever. 



Pickering's second argument for the existence of man- 

 ganese sesquichloride is as follows : — " Seeing that a rise in 

 temperature materially decreases the stability of the higher 

 chloride, whilst a reduction of temperature increases its 

 stability, then, by performing the solution of the dioxide at a 

 sufficiently low temperature, there could be no reason why all 

 of it should not be converted into the higher chloride, if this 

 higher chloride is MnCl 4 , and should be subsequently precipi- 

 tated entirely as dioxide. If, however, the higher chloride 

 formed were Mn 2 Cl 6 , it would only be possible to obtain 50 

 per cent, of the dioxide used." A series of experiments was 

 therefore made, similar in every respect, except that the tem- 

 perature of solution of the dioxide was varied. It was found 

 that when the solution was performed at 10°, 45*5 per cent, of 

 the Mn0 2 was recovered. This amount was only increased to 

 47 per cent, when performed at —20°. Above 10° the per- 

 centage recovered began to decrease more rapidly, till at 61° 

 only 9 per cent, was recovered. That is to say, if pure dioxide 

 had been used, only at the most 42*36 per cent, instead of 

 45*5 per cent, of the original dioxide used would have been 

 recovered. 



Experiments were therefore made to see if it were not 

 possible to recover more than this percentage when pure 

 dioxide was used, or a correspondingly larger percentage when 

 dioxide containing some MnO was used. In these experi- 

 ments a weighed quantity of the dioxide was shaken about 

 with a measured volume of concentrated hydrochloric acid in 

 a flask surrounded by a vessel of water to keep the tempera- 

 ture constant. Five minutes was generally allowed for solu- 

 tion. The liquid was then poured into a large quantity of 

 water, generally about fifty times the volume of the acid used, 

 and the precipitated oxide collected, washed, and heated with 

 hydrochloric acid, the chlorine evolved being estimated in the 

 usual way by passing it into potassium iodide solution. As it 

 was thought possible that not all the dioxide would be dissolved 

 in the hydrochloric acid, but would remain suspended mecha- 

 nically in the solution, and so give a too high result for the 

 dioxide recovered, it was in several cases placed on a small 

 filter, and hydrochloric acid allowed to drip on it slowly, the 

 filtrate passing into a vessel of water, and being so precipi- 



