24 M. Bonsdorff on the Use of Tincture and Brazil Wood [Juxx, 
acid produces an alteration of colour, which is'sometimes similar 
in various acids, but which is most commonly different from that 
produced by the acid diluted with water; secondly, different 
acids produce their effects in different times ; and thirdly, the 
colour produced by the action of different acids is more or less ' 
durable, and it undergoes changes in a shorter or longer time. 
It is with respect to these variations that we ‘now propose to 
consider the acids; and to give the reader an opportunity of 
judging by ‘comparison, we shall successively enumerate the 
miost common acids, and even those which do not possess a very 
marked action. 
Concentrated sulphuric acid, or when mixed with three parts 
of water, immediately gives a bright rose colour to Brazil wood 
paper, which, by attracting moisture from the air, becomes 
orange-coloured. When diluted with rather more water, the 
acid produces a colour which has a shade of yellow; and with 
20 or 30 parts of water, it gives in one minute a yellow, orrather 
a yellowish colour, which very soon fades. 
Nitric and muriatic acids act nearly in the same way as sul- 
phuric acid, excepting that the yellow colour produced by these 
acids, when diluted with water, is paler; the rose colour pro- 
duced by the concentrated nitric acid soon becomes yellow and 
greyish, and that produced by muriatic acid still sooner becomes 
of a dirty grey colour. The action of the three acids men- 
tioned differs but little; but it may be employed to distinguish 
to a certain extent the degree of concentration of these acids. 
Sulphurous acid gas bleaches the moistened paper perfectly. 
Hydriodic acid, when concentrated, gives a rose colour, which 
gradually becomes yellow on the edges, and in a few days 
entirely yellow. When diluted with water, it gives a fine yellow 
colour in half a minute, which soon begins to fade; in a few 
hours, it becomes less evident, and is rather red than yellow. 
lodic acid immediately gives a pale dirty yellow colour, which 
remains unchanged. 
Concentrated fluoric acid, whether pure or combined with 
silica, gives a bright red colour; when diluted, it acts in a very 
marked manner; it immediately becomes a fine lemon yellow 
colour, which disappears in the space of a minute, and soon 
leaves a greenish grey colour, which, by transmitted light, 
appears ofan olive-green. When the fluoric acid is used in the 
gaseous state, it is sufficient to subject the moistened Brazil 
wood paper to its action fora few seconds. The paper is then 
stained a bright yellow, which disappears in the manner 
already mentioned. This also takes place with other volatile 
acids. 
Fluoboric acid acts in the same way as the fluoric. 
Boracic acid has no immediate action, but the colour of the 
paper soon becomes pale, and is eventually of a reddish-white 
colour. If the boracic acid contains any trace of sulphuric-acid, 
