Chapter II Experimental Technique.pdf

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CHAPTER IT
EXPERIMENTAL
TECHNIQUE
11,1.
COMMON ORGANIC LABORATORY APPARATUS
IT will be useful at the very outset to introduce the student to the
apparatus that is commonly employed in the organic laboratory. Whether
he will personally handle all the types of apparatus to be described will,
of course, depend (i) upon the duration of the course in practical organic
chemistry and (ii) upon the facilities provided by the laboratory. Never-
theless, it is deemed advantageous that the student should, at least,
know of their existence.
Flasks.
Various types of flasks are shown in Fig. //,
1,
1,
a-e.
(a)
(e)
(a)
Flat-bottomed flask (the so-called Florence flask) with vial mouth.
The sizes vary between 50 ml. and 40 litres.
(6) This is similar to
(a)
except that it is provided with a ring neck,
which increases the mechanical strength, prevents breakage when a
stopper is inserted, and provides a means for wiring a stopper in place.
The upper rim is ground flat.
(c) Round-bottomed flask. The common sizes range between 25 ml.
and 50 litres.
(d)
Round-bottomed flask with short ring neck (the so-called bolt-
head flask). This is widely used, particularly in advanced work, and
possesses the advantages given under (6). The common sizes range
between 50 ml. and 20 litres.
(e)
This is the familiar Erlenmeyer or conical
flask. The common sizes range between 25 ml.
and 6 litres.
Beakers.
The usual Griffin form with spout,
Fig. //, 7, 2,
a,
are widely used. Sizes between
30 ml. and 6 litres are available. The tall form
(d)
(b)
without spout (Fig. //, 7, 2 6) occasionally finds
Fig.
//, 7. 2.
application in organic laboratories.
46
[11,1]
EXPERIMENTAL TECHNIQUE
47
Distilling flasks. Fig. //,
1,
3,
a
is the ordinary distilling flask.
The sizes vary between 25 and 5,000 ml.
(6) is the so-called Claisen flask, a distilling flask with two necks; the
thermometer is placed in the neck carrying the side arm. Sizes vary
between 25 ml. and 2,000 ml. It is of particular value hi distillations
where foaming or bumping occurs, and is widely employed in distillations
under diminished pressure.
(c) is identical with (6) except that it is provided with a second long and
indented neck (which is essentially a Vigreux column—see Section 11,15).
It is sometimes termed a Claisen flask with fractionating side arm.
In
(d)
the side arm outlet extends a short distance into the long neck
of the flask, thus preventing any vapour which has been in contact with
cork or rubber stoppers from condensing and flowing down the side arm.
(a)
It is usually employed for those liquids which attack cork or rubber
stoppers.
Condensers. The various types in common use are shown in
(a) is a typical Liebig condenser, which consists of an inner glass tube
surrounded by a glass jacket through which water is circulated. The
inner jacket is fitted into the outer jacket by means of rubber stoppers ;
rubber tubing, formerly used, is less durable and is not recommended.
(6) is an all-glass Liebig condenser of similar design to (a) ; the jacket
is sealed to the condenser tube. Two convenient sizes of condensers,
suitable for general use, have jackets of 20 and 40 cm. length.
In the Pyrex glass West condenser greater efficiency of cooling is
obtained by having a light-walled inner tube and a heavy-walled outer
tube with a minimum space between them.
(c) is the inner tube of a Liebig condenser. It is used as an air-con-
denser when the boiling point of the liquid is above 140-150°.
(d)
is an all-glass Allihn condenser. The condensing tube is made with
a series of bulbs ; this increases the condensing surface and lessens the
resistance to the passage of vapours when the condenser is employed for
48
PRACTICAL ORGANIC CHEMISTRY
[II.
refluxing, i.e., for condensing the vapours issuing from the flask so that the
liquid continuously flows back again.
(e)
is a typical double surface condenser (Davies type). It is far more
efficient than any of the preceding types and the jacket is usually shorter.
0
0
\/
(b)
(c)
(e)
(f)
(g)
Fig.
11,
1,
4.
(h)
(/) is an efficient spiral condenser of the Friedrich type. The hot
vapours can be introduced either at the side or the bottom, thus permitting
the use of the condenser either for condensing vapours from another
reaction vessel or for ordinary reflux purposes.
(g)
is a coil condenser provided with an internal glass coil or spiral.
In a modification there is both an internal spiral as well as an outer cooling
jacket.
1]
EXPERIMENTAL TECHNIQUE
49
(h)
is a Dewar type of reflux condenser. It is usually charged with a
freezing mixture,
e.g.,
Dry Ice mixed with alcohol or acetone.
Funnels. Various kinds of funnels are depicted in Fig. //,
1,
5,
a-f.
to
Fig. //,
I, 6.
(d)
(f)
(a) is
the ordinary 60° filtration funnel. It is convenient in many
operations to employ funnels with a short stem (0-5-1 cm. long) as in (6).
(c),
(d)
and
(e)
are examples of separatory funnels. Type (c) is the
globular form and is the most widely used ;
(d)
and
(e)
are the Squibb
(pear-shaped) and cylindrical separatory funnels respectively. The
funnel (/) is similar to (c) except that it is provided with a device immedi-
ately below the tap which enables the liquid to be added dropwise, the
rate of addition being visible even when the stem of the funnel is immersed
in a liquid : it is termed a dropping funnel.
Hot water funnels. Three varieties of hot water funnel are illustrated
in Fig. //,
1,
6. Type (a) consists of a double-walled copper jacket to
(b)
Fig.
//,
1,
6.
50
PRACTICAL ORGANIC CHEMISTRY
[II,
house the funnel ; it is mounted on a tripod. The space between the
walls is almost completely filled with water, and the water may be heated
to any desired temperature below 100° by directing the flame of a Bunsen
burner on to the side tube. Type (6) consists of a coil made of copper
or lead tubing of about 10 mm. diameter forming a 60° cone ; this will
therefore accommodate any funnel. Hot water or steam is passed through
the coil, hence it is very suitable for the filtration of inflammable liquids.
The funnel may also be used for " cold filtrations " by circulating cold
water through the coil. Type
(c)
is an electrically heated funnel and is
provided with a constant level device. Electric heating mantles (see
Section
II,
57) for both 60° glass funnels and Buchner funnels are commer-
cial products.
Funnels for filtration by suction.
These are illustrated in Fig.
77,7,7,0-0.
(Q)
(b)
(c)
(d)
(f)
Fig.
77,
7, 7.

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