6.2.
PARLODION
FILMS
195
seconds. This gives time to complete any solvent activity that might
involve contaminating layers at the surface of the glass. The slide is
then withdrawn and drained as rapidly as possible. The flat plane of the
glass should be held vertically, the long axis of the slide should be held
obliquely so that excess solution drains quickly across the short axis of
the glass, and then runs down one edge of the slide to a corner. Since
amyl acetate evaporates relatively slowly, drainage essentially is completed before the viscosity of the remaining solution begins to impede
it. Thus the deposited film will be very nearly of uniform thickness
except at the draining edge of the slide. This technique of rapid draining also allows the standardization of film thickness, and the thickness
is quite directly related to the original concentration of Parlodion.
After the film is dried on the glass surface it is floated off the slide on
a clean water surface. For this one needs a good sized glass bowl. Circular
glass baking dishes about 10 in. in diameter serve well [Fig. 22(a)]. One
should take certain precautions to get a clean water surface. The glass
bowl itself should be clean, of course. Tap water can be used, at least in
some cities. If the water tends to be supersaturated with air, it is best to
let it run from the faucet for a few minutes until only a few bubbles
appear as the bowl is filled. The bowl should be filled to overflowing
and all bubbles allowed to rise to the surface. Then excess water is spilled
over the edge and the clean water surface is ready to use.
The next step is to take a moderately sharp object such as a forcep's
tip and make a rectangular score mark close to the edges of the slide,
around the area of film that is to be removed.
FIG. 22. (a) Parlodion or Formvar films, cast on the surface of ordinary microscope
slides, can be floated off on a water surface as indicated in (a) (the film was smoked to
increase visibility). To do this the edges of the film first are scored, and then moisture
is condensed on its surface by exhaling upon it. The slide is held at about a 30° angle
as it is pushed down into the water. The film should float away freely from the glass
as shown here. A fairly large glass ''baking dish" should be used for this purpose. It
should be nearly filled with water, and the water surface must be clean.
While the film is floating on the water surface, supporting screens can be laid upon
it (b). They should not be spaced too closely together Each should be tapped with
forceps tips to assure good adherence. If one face tends to be convex, this should be
the face in contact with the film.
After the screens are in place, a dry microscope slide is brought down on top of the
film at about a 30° angle (c) and without delay it is pushed down into the water (d)
and removed face up with the film and screens on top. Excess water is removed with a
bit of filter paper (e) and the screens are ready to use after drying.
PARLODION
FILMS
195
seconds. This gives time to complete any solvent activity that might
involve contaminating layers at the surface of the glass. The slide is
then withdrawn and drained as rapidly as possible. The flat plane of the
glass should be held vertically, the long axis of the slide should be held
obliquely so that excess solution drains quickly across the short axis of
the glass, and then runs down one edge of the slide to a corner. Since
amyl acetate evaporates relatively slowly, drainage essentially is completed before the viscosity of the remaining solution begins to impede
it. Thus the deposited film will be very nearly of uniform thickness
except at the draining edge of the slide. This technique of rapid draining also allows the standardization of film thickness, and the thickness
is quite directly related to the original concentration of Parlodion.
After the film is dried on the glass surface it is floated off the slide on
a clean water surface. For this one needs a good sized glass bowl. Circular
glass baking dishes about 10 in. in diameter serve well [Fig. 22(a)]. One
should take certain precautions to get a clean water surface. The glass
bowl itself should be clean, of course. Tap water can be used, at least in
some cities. If the water tends to be supersaturated with air, it is best to
let it run from the faucet for a few minutes until only a few bubbles
appear as the bowl is filled. The bowl should be filled to overflowing
and all bubbles allowed to rise to the surface. Then excess water is spilled
over the edge and the clean water surface is ready to use.
The next step is to take a moderately sharp object such as a forcep's
tip and make a rectangular score mark close to the edges of the slide,
around the area of film that is to be removed.
FIG. 22. (a) Parlodion or Formvar films, cast on the surface of ordinary microscope
slides, can be floated off on a water surface as indicated in (a) (the film was smoked to
increase visibility). To do this the edges of the film first are scored, and then moisture
is condensed on its surface by exhaling upon it. The slide is held at about a 30° angle
as it is pushed down into the water. The film should float away freely from the glass
as shown here. A fairly large glass ''baking dish" should be used for this purpose. It
should be nearly filled with water, and the water surface must be clean.
While the film is floating on the water surface, supporting screens can be laid upon
it (b). They should not be spaced too closely together Each should be tapped with
forceps tips to assure good adherence. If one face tends to be convex, this should be
the face in contact with the film.
After the screens are in place, a dry microscope slide is brought down on top of the
film at about a 30° angle (c) and without delay it is pushed down into the water (d)
and removed face up with the film and screens on top. Excess water is removed with a
bit of filter paper (e) and the screens are ready to use after drying.