IMPORTANT EXPERIMENTS ON INDIGO. 
341 
lution being of such a strength that a candle tube of a purple colour; the results were as 
appeared when viewed through it in a test- follows 
I 
I 
r’blue. 
Prussiate of potash^ 
Acetate — do. 
Carbonate— do. 
Nitrate — do. 
Sulphate — . do. 
Tartrate — do. 
Muriate — do. 
Iodide of potassium J 
Nitrate of barytes — blue 
Nitrate of silver — liquor turned mouse colour, but no precipitate. 
Nitrate of mercury 1 
Acetate of lead ^blue. 
Nitrate of strontia J 
Solution of gold— colour destroyed 
Muriate of soda ) .1 
Carbonate of soda S 
Borate of soda > , 
Phosphate of soda \ change. 
Muriate of ammonia — no change. 
Nitrate of ammonia — blue. 
Muriate of iron 
Sulphate of iron 
no change. 
Nitrate of copper 
Sulphate of copper 
no precipitate, but one drop of a 
solution of ether caused the flame 
of the candle to appear blue. 
Sulphate of magnesia ) 
Sulphate of zinc i no change. 
All these blue precipitates appeared to be the 
same; being dissolved in sulphuric and boiling 
muriatic acids, forming line blue solutions — 
and forming colourless solutions with nitric 
acid. Mr. Crum supposes cerulin to be a com- 
pound of 1 indigo +4 water. 
At the commencement of the solution of indi- 
go in sulphuric acid there is produced a pur- 
ple liquid, and if the action of the acid is stop- 
ped before cerulin is formed, this purple may 
be insulated, and obtained in a separate state. 
If that acid prepared from the dry proto-sul- 
phate of iron, and called after tbe place at 
which it is made, JNordhausen acid, is used, 
the dilution with water must be made imme- 
diately after solution, but with the common 
acid* it requires two or three hours for its 
formation ; if, however, heat is employed, 
ten minutes is sufficient. After the dilution 
Muriate of lime — blue. 
the whole must be thrown on a filter, a blue 
liquid passes through, and indigo-purple re- 
mains ; this is washed with distilled water 
till the blue colour is extracted, and from this 
the indigo that has been changed may be pre- 
cipitated by muriate of potash, and subse- 
quently washed with distilled water till the 
washings cease to form a white cloud with 
nitrate of silver. The substance remaining 
on the filter Mr. Crum calls phenicin, from 
the Greek word purple; like cerulin, the 
solution iri water is blue, but it is sparingly 
soluble; it was precipitated by every salt I 
tried. It is turned green by caustic alkalies, 
in which it seems to resemble syrup of violets ; 
by standing, however, the green colour soon 
vanished, and a purple powder slowly collected* 
Mr. Crum considers it to be a compound of 
1 indigo -1-2 water. 
PERSPECTIVE MADE EASY. 
(Continued from page 19iJ 
5. The vanishing point of any line be- 
ginning at the picture-sheet is the point in fig. 
2, which terminates the perspective of the 
line when it is extended to an indefinite dis- 
tance from the point where it commences in 
the picture-sheet ; thus, the point e, in fig. 2, 
is, as was shown before the vanishing point 
of the line d e, in the ground plan ; and this 
same point c is the vanishing point of eve- 
ry line running parallel to d e. The vanish- 
ing point of any line h 1, fig. 1 , running le- 
vel with the eye, but inclined to the picture- 
sheet sideways, is found by drawing the 
line c in the ground plan, parallel to k /, 
till it meets the picture-sheet in m ; and 
this point m is the vanishing point in the 
ground plan of the line k I, and of every 
line in the objects to be represented running 
parallel to it. From the points k and w, in 
the ground plan, draw lines k k and m 
perpendicular to a b, in the perspective view, 
cutting the horizontal line passing through 
the point c, in fig. 2, in the points k and 
m, the point m is the vanishing point of 
the line k I ; and if the points k and m are 
joined, theHne k m will be the perspective 
of the line k I when it is indefinitely- 
extended. The point m in the perspec- 
tive view is also the vanishing point of 
* Since it is of importance in all experiments of research to employ pure matevials, it is 
advisable to purify the sulphuric acid used in these experiments, by diluting it with an equal 
weight of distilled water, and allowing it to stand till perfectly clear, afterwards evapora- 
ting in a glass retort containing pieces of platina (to prevent it from breaking), till of the 
strength required; by this means the sulphate of lead, which exists in considerable quantities 
in commercial sulphuric acid, may be completely separated. 
