F P. Dunnington — On the Formation of Deposits, Etc. 175 



We may hence conclude that (1) Vesuvius and Mt. Loa are 

 instructive examples of the effects of the same volcanic forces 

 and methods under different conditions as to rock materials and 

 heat ; and (2) systematic study inside of craters hetween vol- 

 canic eruptions is what the science most needs. 



In another paper, the results of volcanic action will be 

 further illustrated from observations made, the past year and 

 earlier, in the islands of Maui and Oahu. 



Art. XYIIT. — On the formation of deposits of Oxides of 

 Manganese; by F. P. Dunnington. 



In explanation of the transfer of compounds of manganese, 

 which has taken place in the formation of geological deposits, 

 the only agency mentioned in works on chemical geology as 

 taking prominent part is that of carbonated water, forming 

 the soluble manganese bi-carbonate. Dr. Bischof ■ remarks,* 

 " With regard to the formation and alteration of manganese 

 spar, the same relations obtain as in the case of iron spar." 

 However, Fresenius has shownf that bi-carbonate of iron and 

 of manganese are obtained under different conditions. There 

 is possibly a hint of the formation of manganese sulphate 

 given by Kersten,J but it is not definitely mentioned. 



I propose in this article to call attention to the probability 

 that manganese sulphate has taken a very important part in 

 the formation of deposits of manganese ores. 



Bunsen's analytic method for the valuation of manganese 

 ores is based 'upon the fact that an acid solution of a ferrous 

 salt will dissolve the higher oxides of manganese, with the for- 

 mation of a corresponding amount of a ferric salt. Having 

 observed the promptness with which such solutions are effected, 

 I was led to make some examination of the action of similar 

 solutions upon compact forms of oxide of manganese, and 

 further to ascertain some of the conditions under which solu- 

 tions of ferrous sulphate, ferric sulphate and manganese sul- 

 phate are decomposed. With this in view, the following ex- 

 periments were made : 



1st. There was prepared a solution of ferrous sulphate and 

 sulphuric acid in such proportions as would result from the ox- 

 idation of iron pyrites and solution in 25 parts of water. In 

 500 c.c. of this solution, a lump of crystallized pyrolusite was 

 suspended near the toj) of the liquid for 48 hours, resulting in 



* Chem. and Phys. Geol., vol. i, p. 57, trans. Cav. Soc. 

 f Loc. cit., vol. iii, p. 531. 

 \ Loc. cit, vol. i, p. 160. 



