176 F. P. Dunnington — On the Formation of Deposits 



dissolving a thickness of '804 mm. (as calculated from the spe- 

 cific gravity of the mineral, area of the surface exposed and 

 loss of weight) ; a rate of solution equivalent to 6 inches in 

 one year. 



2d. A lump of compact psilomelane was similarly suspended 

 in the acid ferrous solution and a thickness of '506 mm. was 

 dissolved in 48 hours; equivalent to 3*78 inches in one year. 

 In each of the foregoing experiments a corresponding amount 

 (45 and 12 per cent of the total) of the ferrous salt was con- 

 verted to ferric. 



3d. A glass tube 3 cm. in diameter and 20 cm. in length, 

 contracted at one end, was filled with a mixture of coarse 

 powders of psilomelane, 75 grm., disintegrating pyrites (from 

 Marienburg near Bonn), 100 grm. and glass. Through this 

 tube two liters of water were allowed to percolate in the 

 course of 24 hours, and in the liquid was found manganese sul- 

 phate, 7 grm., ferric sulphate, 1*45 grm. and sulphuric acid, 

 4'34 grm. 



4th. Through the above filled tube, two liters more of wa- 

 ter were similarly passed and this dissolved of manganese sul- 

 phate, *154 grm., ferric sulphate, -07 grm. 



5th. Through the above filled tube, two liters more of wa- 

 ter were passed, while a continuous current of air was drawn 

 through the tube ; this dissolved of manganese sulphate *292 

 grm., with about '07 grm. of ferric sulphate. 



6th. The glass tube was then refilled, as at first, but using a 

 bright granular pyrite (from Louisa Co., Ya.). The current 

 of air was kept up, and two liters of water, dropping at a uni- 

 form rate, were passed through the tube in the course of 

 twenty-one days; this dissolved of manganese' sulphate '098 

 grm. and no iron, while a small amount of ferric hydrate was 

 formed and remained in the tube. 



7th. A neutral solution of ferrous sulphate digested cold 

 with manganese carbonate, air being excluded, no change takes 

 place ; but when heated to 100° C. for two hours, considerable 

 manganese sulphate and ferrous carbonate were formed. 



8th. Ferric sulphate solution reacts immediately upon man- 

 ganese carbonate, forming manganese sulphate, ferric hydrate 

 and carbonic acid. 



9th. By reason of the fact, which is familiar, that ferrous 

 sulphate solution is rapidly oxidized when exposed to the air, 

 we find that when it is in contact with manganese carbonate, 

 in the presence of air, the manganese carbonate is decomposed, 

 forming manganese sulphate, etc., as above. 



10th. A neutral solution of ferrous sulphate with calcium 

 carbonate, sealed in a tube under carbonic acid, was heated to 

 100° C. for two hours ; mutual decomposition took place, 

 forming ferrous carbonate and calcium sulphate. 



