Phenomena of the Rainbow. 203 



These observations having been suggested by your remark, 

 I I ><.'<; leave to address them to you, and to place them at your 

 disposal. 



Remaining, my dear Sir, yours very respectfully, 



ALFRED AINGER, 



To M. Faraday, Esq. 

 &c, &c. &c. 



ON THE MODE OF ASCERTAINING THE COMMERCIAL 

 VALUE OF ORES OF MANGANESE. 



BY EDWARD TURNER, M.D., F.R.S. L. andE., SEC. G.S. 

 Professor of Chemistry in the University of London. 



fPHE analysis of the ores of manganese, when pure, is ex- 

 ceedingly simple. The operator need only, by well known 

 methods, determine the water which the ore contains, and the 

 oxygen which it loses in being converted into the red oxide. 

 Its degree of oxidation, on which the commercial value of ores 

 of manganese so essentially depends, may then be readily 

 inferred. 



But when impurities prevail, as they almost always do, 

 more or less, in commercial manganese, the analytic process 

 is complex and troublesome ; and the presence of iron, which 

 is rarely absent, renders an exact result by the ordinary modes 

 of analysis almost impracticable. For, as I have elsewhere 

 stated*, when peroxide of iron is strongly heated in mixture 

 with peroxide or deutoxide of manganese, oxygen is given out 

 by the former as well as by the latter ; and, accordingly, the 

 oxygen lost by heat ceases to indicate the nature of the man- 

 ganese. A moderately correct allowance for the quantity of 

 oxygen emitted by the iron under these circumstances would 

 be difficult, even after ascertaining in the moist way the quan- 

 tity of iron contained in the ore ; since the constitution of the 

 resulting oxide of iron, as well as its uniformity, is probably 

 variable, and, at all events, is undetermined. The chemist 

 would, therefore, have to ascertain separately each constituent 



* Brewster's Journal of Science, N.S. ii, 213. 



