186 Mr. Brown mi the Commercial Value of Black Oxide of Manganese. 



By another method the equivalent of binoxide per cent, was found to 

 be 55-99. 



This method is very convenient, both from the short time it takes to 

 make an experiment, and from the small number of weighings required ; 

 it also yields very correct results. 



The next method is that of Gay Lussac, which is effected by chlor- 

 imetry. The manganese is weighed out and conveyed into a flask with 

 a bent tube passing into an inverted retort, into which a certain quantity 

 of water with a little caustic lime is introduced. Muriatic acid is then 

 poured on the manganese, and a slight heat is applied, the chlorine is 

 evolved, and is absorbed by the milk of lime. After all the chlorine is 

 disengaged, the milk of lime is taken out and tested, and from the amount 

 of chlorine, the amount of per centage of binoxide of manganese is calcu- 

 lated. The milk of lime containing the chlorine is then tested by the 

 method of Gay Lussac, which consists in the conversion of arsenious 

 into arsenic acid : and from the amount of chlorine taken to convert the 

 arsenious into arsenic acid, the binoxide of manganese is calculated. 



Instead of arsenious acid, a solution of the nitrate of the protoxide of 

 mercury may be employed. When the chlorine is added to this solution, 

 a precipitate of dichloride of mercury or calomel immediately falls, and as 

 more chlorine is added, more dichloride of mercury is precipitated, till all 

 is thrown down, when immediately on the addition of a few drops more, 

 the whole disappears, since the dichloride of mercury is quite soluble in a 

 slight excess of chlorine, being converted into corrosive sublimate. 

 Whenever the liquid becomes quite clear, the process is to be stopped. 

 As a certain quantity of nitrate has been taken, the amount of chlorine 

 will be obtained in the quantity of liquor which it took to dissolve the 

 chloride of mercury, and from that the quantity in the whole liquid, and 

 thence the quantity of binoxide of manganese in the specimen. 



The next method consists in the conversion of binoxide of manganese 

 into protoxide, by reduction by hydrogen gas. The first stage to effect 

 this, is to ascertain the amount of water contained in the specimen. The 

 binoxide of manganese is weighed out in the bulb of a hard chloride of 

 calcium tube, and then heated gently in a current of dry air. The air is 

 drawn over it by an aspirating vessel, and is first passed through sul- 

 phuric acid, which dries it ; it then passes over the manganese, and car- 

 ries off the water, which is caught in a tube containing chloride of 

 calcium. When all the water is driven off, the manganese is allowed to 

 cool, and then weighed ; the decrease in weight in the binoxide of man- 

 ganese, and the increase in the chloride of calcium gives the quantity of 

 water contained in the amount of manganese taken. After the water is 

 driven off and weighed, the apparatus is then put up again, only the 

 aspirating vessel is not required, but a flask containing zinc is fastened on 

 at the other end. The whole apparatus being then made quite air tight, a 

 little water and sulphuric acid are poured on the zinc so as to evolve 

 hydrogen, which is dried by passing it through sulphuric acid, and is 



