On the Cause of the Changes of Colour in Mineral Cameleon. 291 
furnish the means of directing a steam-vessel to any given point, 
even in opposition to a moderate wind and tide, without the aid 
of a man aboard, for a limited time :—if therefore such a vessel had 
been fitted up as a fire-ship, the Algerine navy might have been 
destroyed without the loss of a man on our part. 
On some future occasion I may, perhaps, send you some ob- 
servations on the subject of towing vessels by means of steam- 
boats; On the best forms to give steam-vessels intended for the 
sea; On the utility of a change likewise in the form of sailing- 
vessels ; On the practicability of employing steam as a moving 
power aboard vessels without the possibility of an explosion:—but. - 
for the present I feel I have already trespassed too much on 
your valuable space ; and therefore remain 
Yours, &c. 
4, George’s Place, Dublin, JaMEs Dawson, 
Sept. 14, 1817. 
XLVIIL. On the Cause of the Changes of Colour in Mineral 
Cameieon. By M.CuHEvrevc*. 
en Siyce the time of the illustrious Scheele many important 
facts have been added to the history of manganese; but no per- 
son, tomy knowledge, has made any particular inquiry into the 
cause of the changes of colour exhibited by mineral cameleon t. 
I will endeavour in this note to deduce from observations of my, 
own, an explanation which, if it is admitted, will be susceptible 
of many new applications. 
2. I must begin by stating the properties which Scheele has 
recognised in mineral cameleon. 1. On the solution of came- 
leon in water, a deposition of a fine yellow powder takes place, 
and the liquor passes insensibly to a blue colour. Scheele be- 
lieves that the yellow powder consists chiefly of the oxide of iron; 
that the blue is the true colour of the cameleon, and is only 
changed when iron is in conjunction, 2. Cameleon mixed in 
water becomes decomposed; the mixture appears violet, then 
red; and when the red particles combine, the red colour disap- 
pears and the deposit of cameleon presents nothing more than 
the natural colour of the oxide of manganese. 8. Lastly, the 
same effect takes place when a few drops of acid are added to 
the solution, or when it is exposed for some days to the open 
air: in this last case the alkali unites itself to the carbonic acid 
of the atmosphere. Let us now pass to the facts which I have 
observed. 
* From a work on Manganese, by M. Chevreul. , p 
t The substance so called is a combination of potash with an oxide of 
manganese, 
T2 3. I 
