CHLORINE.
150. Preparation.
Experiment 87.--Put into a t.t. 5 g. of fine granular MnO2 and 10
cc. HCl. Apply heat carefully, and collect the gas by downward
displacement in a receiver loosely covered with paper (Fig. 39).
Add more HCl if needed. Have a good draft of air, and do not
inhale the gas. If you have accidentally breathed it, inhale
alcohol vapor from a handkerchief; alcohol has great affinity for
Cl. Note the color of the gas, and compare its weight with that
of air.
MnO2 + 4 HCl = MnCl2 + 2 H2O + 2 Cl. How much Cl can be separated
with 5 g. MnO2?
If preferred, a flask may be used for a generator instead of a
t.t. Cl can be obtained directly from NaCl by adding H2SO4 (which
produces HCl) and MnO2. 2 NaCl + 2 H2SO4 + MnO2 = MnSO4 + Na2SO4
+ 2 H2O + 2 Cl. Try the experiment, using a t.t. and adding
water.
151. Cl from Bleaching-Powder.
Experiment 88.--Put a few grams of bleaching- powder into a small
beaker, and set this into a larger one. Cover the latter with
pasteboard or paper, through which passes a thistle-tube reaching
into the small beaker (Fig. 40). Pour through the tube a little
H2SO4 dilated with its volume of H2O.
152. Chlorine Water.--A solution of Cl in water is often useful,
and may be made as follows:-- Experiment 89.--To 3 or 4 crystals
of KClO3 add a few drops of HCl. Heat a minute, and when the gas
begins to disengage, pour in 10 cc. H2O, which dissolves the gas.
2 KClO3 + 4 HCl = 2 KCl + Cl2O4 + 2 H2O + 2 Cl.
153. Bleaching Properties.
Experiment 90.--Put into a receiver of Cl, preferably before
generating it, two pieces of Turkey red cloth, one wet, the other
dry; a small piece of printed paper and a written one; also a red
rose or a green leaf, each wet. Note from which the color is
discharged. If it is not discharged from all, put a little H2O
into the receiver, shake it well, and state what ones are
bleached.
Experiment 91.--(1) Add 5 cc. of Cl water to 5 cc. of indigo
solution. (2) Treat in the same way 5 cc. K2Cr2O7 (potassium
dichromate) solution, and record the results.
Indigo, writing-ink, and Turkey red or madder, are vegetable
pigments; printer's ink contains C, and K2Cr2O7 is a mineral
pigment. State what coloring matters Cl will bleach.
154. Disinfecting Power.
Experiment 92.--Pass a little H2S gas from a generator into a
t.t. containing Cl water. Look for a deposit of S. Notice that
the odor of H2S disappears. H2S + 2 Cl = 2 HCl + S.
155. A Supporter of Combustion.
Experiment 93.--Sprinkle into a receiver of Cl a very little fine
powder or filings of Cu, As, or Sb, and notice the combustion.
Observe that here is a case of combustion in which O does not
take part. Chlorides of the metals are of course formed. Write
the reactions. See whether Cl will support the combustion of
paper or of a stick of wood.
Experiment 94.--Warm 2 or 3 cc. of oil of turpentine (C1OH16) in
an evaporating-dish; dip a piece of tissue paper into it, and
very quickly thrust this into a receiver of Cl. It should take
fire and deposit carbon. C1OH16 + 16 Cl = ? Test the moisture on
the sides of the receiver with litmus. Clean the receiver with a
little petroleum.
Experiment 95.--Prepare a H generator with a lamp-tube bent as in
Figure 41. Light the H, observing the cautions in Experiment 23,
and when well burning, lower the flame into a receiver of Cl.
Observe the change of color which the flame undergoes as it comes
in contact with Cl. Give the reaction for the burning. Test with
litmus any moisture on the sides of the receiver. A mixture of Cl
and H, in direct sunlight combines with explosive violence;
whereas in diffused sunlight it combines slowly, and in darkness
it does not combine. From these experiments state the chief
properties of Cl, and what combustion it will support.
[Figure 41.]
156. Sources and Uses.--The great source of Cl is NaCl, though it
is often made from HCl. Its chief use is in making bleaching-
powder, one pound of which will bleach 300 to 500 pounds of
cloth. Cl is very easily liberated from this powder by a dilute
acid, or, slowly, by taking moisture from the air. Hence its use
as a disinfectant in destroying noxious gases and the germs of
infectious diseases. Cl attacks organic matter and germs as it
does the membrane of the throat or lungs, owing to its affinity
for H.
Cl is the best bleaching agent for cotton goods. It is not
suitable for animal materials, such as silk and wool, as it
attacks their fiber. It does not discharge either mineral or
carbon colors. The chemistry of bleaching is obscure.
As dry material will not bleach, Cl seems to unite with H in H2O
and to set O free. The O then unites with some portion of the
coloring matter, oxidizing it, and breaking up its molecule.
Colors bleached by Cl cannot be restored.