272 Contributions towards [Oct. 



proposed by Mr. John Davy. I do not know whether it has 

 ever been put in practice. 



2. The preceding paper contains only a part of Dr. John's 

 experiments on manganese. We shall publish the sequel of his 

 experiments in our next Number. The results which he obtained 

 in his endeavours to determine die number and composition of 

 the oxides of manganese will be there seen. He obtained three 

 oxides, the colours and composition of which were as follows: 



1. Green, composed of 100 metal + 15 oxygen. 



2. Brown, 100 + 25 



3. Black, 100 + 40 



Berzelius has given us the result of his experiments on the 

 oxides of manganese (Larbok i Kemien, t. ii. p. 129). Accord- 

 ing to him there are five oxides of manganese. He obtained 

 the first by keeping manganese for two years in a very well- 

 corked glass. It fell down into a brownish grey powder, which 

 filled the whole of the phial. It was semicrystalline, and had 

 the metalline lustre. He found it composed of 100 metal and 

 7*0266 oxygen. He deduces the composition of the other 

 oxides of manganese, partly from his own experiments, and 

 partly from those of other chemists, as follows : — 



Metal. Metal. Oxygen. 



1. Composed of 100+ 7*0266 oxygen, or 1 + 1 



2 100 + 1+0533 1+2 



3 100+ 28-1070 1 + 4 



4 100 + 42-16 1 +6 



S 100+ 56*213 1 + 8 



Sir Humphry Davy has given us the result of his experi- 

 ments on the oxides of manganese. He obtained two oxides ; 

 the first dark olive, the second brownish black. He found their 

 composition as follows [Elements of Chemical Philosophy, vol. i. 

 p. 367) :— 



Metal. 



1. Olive 100 + 26*58 oxygen 



2. Brown 100 + 39*82 



It is hardly necessary to mention the experiments of Bergman, 

 as they were made at a time when accuracy could scarcely be 

 expected. He obtained three oxides, which he found composed 

 as follows: — 



Metal. 



1. Composed of 100 +25 oxygen 



2 100 + 35 



3 100 + 66-6 



