Illustrated Guide to Home Chemistry Experiments

Chapter 18 Laboratory: Colloids and Suspensions 327

CUTIOA nS

To state the obvious, we’re making napalm, or at least

something very close to napalm. Napalm burns furiously,

sticks to anything it touches, and is very difficult to

extinguish. Use extreme caution when preparing the sol.

Have a fire extinguisher ready, and make absolutely sure

that there are no open flames, sparks, or other potential

ignition sources nearby. Work outdoors if possible, or at

least in an area with excellent ventilation. Do not ignite the

product indoors. Wear splash goggles, heavy-duty gloves,

and protective clothing.

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7.eigh out a final 5 g of polystyrene foam, and continue W

adding it in chunks to the beaker, using the stirring rod to

make sure that the foam you add is incorporated in the

gelled sol. After a total of 35 g of polystyrene foam has

been added, the contents of the beaker will appear to be

completely gelled, with no liquid visible. At this point, the

gelled sol is semi-rigid, enough so that it resists the force

of gravity if the beaker is inverted, as shown in Figure 18-4.

(Don’t invert the beaker indoors, as the gelled sol might

fall out unexpectedly.)

FIGURE 18-4:
The gelled sol is rigid enough to resist the force of gravity

8.f you are not already outdoors, take the beaker to a safe I

outdoor location with a nonflammable surface such as

dirt, gravel, or concrete. (Remember that asphalt, made

from tar, is flammable.) Invert the beaker, and wait a few

moments to see whether the gelled sol separates from

the beaker. If not, tap the beaker gently to release the

gelled sol. When the gelled sol separates, note that it

retains its form, as shown in Figure 18-5. There should

be little or no liquid gasoline remaining. (The stain visible

to the right of the gelled sol in Figure 18-5 is a small

amount, probably less than 1 mL, of liquid gasoline that

was not incorporated in the sol.)

FIGURE 18-5: Although it is technically a liquid, the gelled sol

maintains its form as though it were a solid

dUL. pR A joNES CommENTS:

Be cautious with substances that you haven’t used before.

We’ve had good luck taping a match to the end of a metal

rod for igniting hydrogen balloons and methane bubbles.

That might be a good idea here.

9.ake sure that you have a fire extinguisher handy, and M

verify that there are no children or pets in the vicinity (or

indeed, any other life forms who are unaware of what’s

going on). After you have verified that it is safe to do so,

note the time and use the lighter or match to ignite the

napalm. While the napalm burns, as shown in Figure

18-6, note your observations, including the appearance

and intensity of the flame, whether the flame spreads

or stays in one place, how long the flame continues, any

unusual odor, and so on.

CUTIOA n

Keep all gasoline containers, including the 50 mL of liquid

gasoline (until needed), far away from the ignition site.