each constituent of which is coloured. 421 
is precisely similar to that of bromine, except that the red ray is 
gradually cut off, as with other copper salts. On diluting this 
solution a complete change of colour ensues ; it acquires the blue 
colour and the prismatic appearance of a compound of oxide of 
copper with a colourless acid, as represented in fig. 9. 
Ozxybromide of Tron is intensely red. It gives the same pris- 
matic spectrum as bromine-water does. 
CHLORIDES. 
Chlorine gas absorbs the more refrangible rays; chlorine-water, 
though yellow, cannot be obtained strong enough, even at a tem- 
perature of nearly 0° C., to show any very decided effect on the 
spectrum ; nothing, in fact, beyond a diminution in the inten- 
sity of the violet. Yet in some of its compounds its absorbent 
power is well marked. 
Terchloride of Gold gives a yellow solution, and absorbs more 
blue than the yellowish-green nitrate does. Compare figs. 19 
and 15. The acid hydrochlorate of this salt is indistinguishable 
from it by the prism, though to the unaided eye it appears of a 
somewhat purer yellow. 
Bichloride of Platinum transmits scarcely any rays more refran- 
gible than b, unless the stratum be very thin, when a little blue 
and violet pass. See fig. 20. he sulphate, fig. 16, admits 
more rays, especially in the neighbourhood of F. 
Bichloride of Palladium isred: it transmits the red and orange 
rays freely, the yellow and green but partially, and the blue only 
where the stratum is very thin. See fig. 23. 
Chloride of Copper in saturated aqueous solution is green: it 
shows the absorption of the red ray due to the metal ; but the 
rays more refrangible than 4 are likewise absorbed. See fig. 21. 
If water be added to this solution, it suffers the same change as 
the green bromide does, becoming blue, and admitting all the 
more refrangible rays, like any ordinary salt of copper. 
Sesquichloride of Iron gives a solution of a reddish-orange 
colour when concentrated, and the prismatic appearance of fig. 8. 
If water be added, it becomes more yellow in colour, and admits 
the same rays as the nitrate does. See fig. 4. Of course in this 
and similar cases it will be understood that the light is made to 
pass through the same amount of salt, whether it be diffused 
through much or little water; a circumstance that in ordinary 
cases makes no difference in the absorption or transmission of rays. 
Chloride of Nickel, when dissolved in very little water, is of a 
yellowish-green. It then absorbs, not only the red ray, as nickel 
salts always do, but nearly all the light beyond F besides. When 
more water is added it becomes of a bluish-green, and shows the 
absorption due to the metal alone. See figs. 1] and 10, 
