132 Dr. Forrhhammer on the [Aug. 



• the green solution contains more oxygen than the peroxide on 

 this account; and because it forms certain compounds with alka- 

 Ues I have named it manganeseous acid. 



The necessity of adding potash together with a body absorbing 

 oxygen appears contrary to this opinion ; but this is owing to 

 the very weak nature of the manganeseous acid, its very 

 existence depending entirely on the presence of potash (or some 

 other alkali) and water. The compound of manganeseous acid 

 and potash is a submanganesite. Whenever the potash is satu- 

 rated, or its action weakened, the manganeseous acid is imme- 

 diately decomposed nito deutoxide of manganese andmanganesic 

 acid. It will be very easy to explain by this fact all the difterent 

 phenomena which the chamecleon show«. A green solution, 

 when exposed to the air, turns red, by the absorption of carbonic 

 acid, which always precipitates deutoxide of manganese ; sul- 

 phuric and nitric acid have the same effect, and even water will 

 do the same, when added in great quantity, as it weakens the 

 power of the potash ; just as that hquid precipitates the oxide of 

 bismuth from its nitric solution. It is the same thing with the 

 reduction of the red colour to the green, which best takes place 

 when an alkali and some matter absorbing the oxygen are added 

 together ; but that it is not absolutely necessary in every case 

 to add alkali is proved by an experiment quoted by Chevreul, 

 who obtained green chameeleon, when he filtered red chamceleon 

 through paper. It is plain that by the contact of the paper 

 some oxygen from the manganesic acid was absorbed. This 

 reduced it to manganeseous acid, and gave it the green colour. 



Let me remark here a very interesting fact in respect to the 

 changes which the difterent oxides of manganese undergo by 

 acids and alkalies. The deutoxide of manganese, when boiled 

 with nitric or sulphuric acid, is entirely converted into protoxide, 

 which is dissolved, and black peroxide: the peroxide, when 

 heated with potash, is changed into manganeseous acid, which 

 combines with the alkali, and into deutoxide of manganese. The 

 manganeseous acid, when combined with potash is, by acids, 

 changed into the soluble manganesic acid and deutoxide, and 

 perhaps the manganesic acid, treated in a gentle heat with 

 potash, would form a still higher degree of oxidation and manga- 

 neseous acid. 



I prepared a solution of manganesiate of potash by passing 

 carbonic acid through a solution of submanganesite of potash. 

 When the red colour was no more altered by the carbonic acid, 

 I separated the clear red liquid from the precipitated deutoxide 

 of manganese, and added sulphuric acid. Exposed to sponta- 

 neous crystallization, it let fall crystals of sulphate of potash, of 

 manganesiate of potash, as the French chemists have described 

 them, and of bisulphate of potash, which shows that the sulphu- 

 ric acid, if it decompose the manganesiate of potash at all, only 

 decomposes it when it can form bisulphate of potash, which 



