CHEMICAL SCIENCE. 213 



when heated to ebullition, a lively effervescence of sulphuretted hydro- 

 gen takes place and there is an immediate deposition of magnesia. 

 Comptes Rendus,July, 1852. 



ON THE SEPARATION OF MANGANESE. 



DR. GIBBS in a communication to Silliman's Journal, September, 

 1852, gives the following statements in regard to the precipitation ol 



manganese 



Schonbein in a memoir on the relations of peroxide of lead and 

 ozone, has pointed out the remarkable fact that peroxide of lead 

 precipitates manganese completely from its solutions in chloro-hydric 

 and sulphuric acids, a compound of peroxide of lead and peroxide of 

 manganese being formed. A portion of the lead is at the same time 

 reduced to protoxide and unites with the acid with which the manga- 

 nese was combined. Schonbein appears not to have remarked the 

 importance of this observation in an analytical point of view. 



In investigating the subject carefully, I have been led to the con- 

 clusion that the peroxide of lead constitutes one of the most valuable 

 re-agents in analytical chemistry, since by means of it the oxide 01 

 manganese may be easily and completely separated from a number 

 of other bases, without the employment of ammoniacal salts. The 

 use of ammonia, as is well known, frequently renders analyses con- 

 ducted by the ordinary methods laborious and inaccurate, either from 

 the number of operations involved, from the absorption of carbonic 

 acid from the air, or from the unavoidable loss in driving off the 

 ammoniacal salts by heat. The fact which I have determined, and 

 which serve as the basis of the analytical application of the peroxide 

 of lead are as follows : 



Peroxide of lead completely precipitates manganese from neutral 

 solutions in chloro-hydric, sulphuric and nitric acids, slowly in the 

 cold, but very rapidly by digestion or by boiling. The presence of 

 an excess of chloro-hydric or sulphuric acid does not prevent the com- 

 plete precipitation of the manganese ; in these cases, however, chlo- 

 rine or oxygen is set free, and the quantity of lead dissolved is 

 greater than that which corresponds to the quantity of manganese 

 precipitated. Such an excess of acid should be avoided as far as 

 possible. 



The presence of an excess of nitric acid prevents the precipitation 

 of the manganese, since hyper-manganic acid is formed and remains 

 in solution. Tartaric acid, and those organic substances which are 

 burned at the expense of the peroxide of lead, do not interfere with 

 the precipitation of the manganese. The organic matter is first 

 destroyed by the oxygen of the peroxide of lead, and afterwards the 

 manganese is precipitated by the excess of the peroxide added. 

 When the quantity of organic matter present is large, it is always 

 better to separate the manganese by means of sulphydrate of ammo- 

 nium in the usual manner. "When, however, oxalic acid is present, 

 we may avoid the use either of an inconvenient quantity of peroxide 



