A Gallery of Beta - Naphthyl Acetate Photomicrographs

(using a variety of illumination techniques)

by Brian Johnston   (Canada)

Beta-naphthyl acetate seems to be a compound that is not commonly used outside of biological research.  There is some indication that it is an intermediate in the production of some scent producing substances for the fragrance industry.

As can be seen in the structural formula and molecular shape shown below, the structure is based upon two attached benzene rings.  (Both illustrations were produced by HyperChem Pro.)

The very low melting point of the white powder, about 69 degrees Celsius, allows the easy production of a melt specimen by heating a small sample between microscope slide and cover-glass.  Little research seems to have been done on the dangers involved in the use of beta-naphthyl acetate.  The MSDS safety document contains the following.

Caution! The toxicological properties of this material have not been fully investigated. May cause eye and skin irritation. May cause respiratory and digestive tract irritation.

Most photomicrographs of melt specimens of the compound show evidence of a multitude of tiny gaps between the crystals.  These gaps appear light gray in the polarized light images below.  Two lambda/4 compensators were used to produce the gray background, rather than the normal black.

The edges of individual crystals can be more easily distinguished when dark-ground illumination is used.  In the case of the two images that follow, a normal objective was paired with one of the annular rings of a phase-contrast condenser in order to produce the dark-ground effect.  (A normal dark-ground condenser would not produce the subtle colouration seen below.)

Here again, polarized light, with two lambda/4 compensators helped produce the colouration.  Can you see that both photomicrographs are of exactly the same field?  The circular lambda/4 compensator was rotated slightly to produce the dramatic difference in the appearance of the two images.

Three more images using the same illumination technique follow.  The higher magnification shows the gaps between crystals more clearly.

Larger structures sometimes form.  The left image uses the same illumination as the images immediately above.  The right image uses crossed polars with no compensators.

Needle-like structures sometimes occur.

In the image that follows, one of the two lambda/4 compensators was replaced by a lambda compensator.  In this case, the gaps between crystals are orange in colour.

A much higher magnification reveals the detail at the edge of a gap (black).

In the next group of five images, the polarizing condenser has been replaced by a phase-contrast one.  A normal, (non-phase) objective was used to form the image.  By experimentation, a particular annular ring of the condenser was chosen to produce the desired effect.

For comparison, here is a similar field using a normal dark-ground condenser.

Again for comparison, a similar field at higher magnification is imaged by using a normal phase-contrast configuration (with phase objective).

Since compounds like beta-naphthyl acetate have been removed from high school chemistry labs for safety reasons, it has become almost impossible to obtain tiny samples for microscopic examination.

Photomicrographic Equipment

The images in the article were photographed using a Nikon Coolpix 4500 camera attached to a Leitz SM-Pol polarizing microscope.  Images were produced using several illumination techniques: dark-ground, phase contrast and polarized light.  Crossed polars were used in all polarized light images.  Compensators, ( lambda and lambda/4 plates ), were utilized to alter the appearance in some cases.  A 2.5x, 6.3x, 16x or 25x flat-field objective formed the original image and a 10x Periplan eyepiece projected the image to the camera lens.

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Published in the March 2007 edition of Micscape.
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