Royal Institution. 323 



the sulphuret. On treating the mass with water and filtering the 

 fluid, a solution of sulphate of manganese will be obtained which 

 will yield a white precipitate with the ferrocyanide of potassium, 

 without a trace of iron. 



Similar experiments may be made with any manganese ores, or 

 with substances known or suspected to contain manganese. The 

 quantity of materials operated on may be increased or diminished at 

 pleasure ; but if increased, the heat should be continued a little 

 longer, to decompose any remaining sulphuret, and thus add to the 

 quantity of sulphate formed. In the same way manganese was 

 detected in some minerals in which it was known to exist, and in 

 others in which it had not been previously found ; likewise in soils 

 and subsoils, in the ashes of coal and peat, in a number of pigments, 

 and also in the ashes of different fabrics partially dyed brown by 

 manganese. 



Sulphate of manganese is formed, with sulphuret, when sulphurous 

 acid gas is made by heating a mixture of peroxide of manganese and 

 flowers of sulphur, even in close vessels. The sulphate may also be 

 more readily obtained, in quantity, by simply boiling a solution of 

 common green vitriol in water for about a quarter of an hour or 

 upwards, in contact with an excess of sesquioxide of manganese in 

 fine powder, till the solution affords a white precipitate with ferro- 

 cyanide of potassium. 



Chloride of manganese may also be formed in a similar manner by 

 boiling an aqueous solution of protochloride of iron with an excess 

 of sesquioxide of manganese, or it may be made with greater facility 

 by dissolving this oxide in the common muriatic acid of commerce, 

 taking care that the oxide be present in excess. 



The brown sesquioxide of manganese may be made, not only by 

 means of sulphur, but more readily and better by mixing the com- 

 mon peroxide with about one-third of its weight of peat mould, saw- 

 dust or starch, and exposure to a red heat in an open crucible with 

 occasional stirring for about a quarter of an hour, or until tlie oxide 

 acquires a uniform brown colour. 



The sulphate and chloride of manganese being extensively used 

 in dyeing, calico-printing and other arts, and in making the com- 

 jjounds of manganese, the simj)le means stated of forming those 

 salts, free from iron (it is presumed), are material improvements on 

 the circuitous methods hitherto adopted. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



Jan. 27, 18.54. — On the Vibration and Tones produced by the 

 Contact of Bodies having different Tem])eratures. By John Tyn- 

 dall, Esq., Ph.D., F.R.o., Professor of Natural Philosophy, Royal 

 Institution. 



In the year 1805, M. Schwartz, an inspector of one of the smelt- 



