1824.] M. Gay-Lussac on the Chloride of Lime. 221 



of lime to be perfectly pure, and formed as stated in page 219, 

 it contains per kilogramme 101*21 litres of chlorine. 



The base I have adopted appears to deserve the preference, 

 from the simplicity and precision of expression that it admits of 

 in chlorometry, which may remain unchanged, whatever means 

 may be used to measure the strength of the chlorine. 



We obtain more precision in general with a weak solution of 

 chloride, marking for instance 4 or 5 degrees, than with a very 

 concentrated solution. If, therefore, on the first trial we find that 

 the chloride much exceeds 10°, we must add a known volume 

 of water to the solution, for instance, twice its bulk; we then 

 make a fresh trial, and triple the number of degrees obtained to 

 get the true value of the chloride. 



Assay of the Oxide of JSIanganese. 



The purity of the oxides of manganese, employed in pre- 

 paring the chlorine, is very variable, and consequently that of 

 any particular ore must be ascertained by experiment, which 

 may be easily done, in the following manner. 



Pure peroxide of manganese is formed of, 



Manganese 3*5578 grammes 



Oxygen 2*0000 



5-5578 



and furnishes 4*4265 gram, of chlorine, o\ 1*3963 litre, at the 

 temperature of 0°, and under a pressure of 0*76 m ; consequently 

 3*980 gram, would produce 1 litre of chlorine, and 1 kilogramme 

 would produce 251*23 litres. 



We take, therefore, 3*98 gram, of the oxide of manganese 

 which we wish to assay, and treat it with muriatic acid, with a 

 gentle heat, receiving the disengaged chlorine in rather less than 

 a litre of milk of lime ; towards the end of the operation we make 

 the acid boil, to drive the chlorine from the vessels into the 

 milk of lime, and add water to make its quantity just one litre. 

 The quality of this chloride will exactly give that of the oxide 

 of manganese. 



The value of the manganese does not depend wholly on the 

 quantity of chlorine it is capable of furnishing, but also on that 

 of the muriatic acid required for its production. But the ope- 

 ration is delicate, and the low price of muriatic acid makes it 

 unnecessary. I shall only remark, that the peroxide of man- 

 ganese often contains the carbonates of lime, barytes, and iron, 

 which saturate to mere loss a portion of the muriatic acid ; 

 moreover, as the manganese is not always in the state of per- 

 oxide, the quantity of muriatic acid required will not in that 

 case be proportionate to that of the chlorine obtained. 



