M I C R O N PROBES
for superimposing the x-ray and electron images and for monitoring x-ray and electron intensities. This permits direct visual comparison between the surface topography of the specimen and the distribution of a selected element. The electron beam, accelerated in a range of 4 to 50 kv., is focused by means of magnetic lenses to a diameter of less than 1 micron. By means of scanning coils, the beam can scan up to y 2 sq. mm. Some of the electrons striking the surface are reflected with little loss of energy and others penetrate the surface and excite emission of x-rays. Resolution of the elec tron image is better than 1 micron and resolution of the x-ray image is approximately 1 micron. The range of elements is from atomic number 12 to 92. The rotatable specimen table holds one specimen and 13 pure metal standards. The usual range for specimens is 1/i" diameter up to 1 / g " long. Specimens and standards can be changed without destroying the vacuum. Larger samples can also be handled. The specimen may be rotated about the optical axis. An optical microscope with an 88X or 36X mag nification is used to view the samples.
Standard Aerograph 110-C is complete with Brown 1 mv recorder. Price $1785.
What the
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Can Do for You New columns and packings have greatly extended the usefulness of the Aerograph. It operates to 300° C with quantitative sample collection. Here are some of the many analyses the research chem ist can perform with this economical instrument: FATTY ACID METHYL ESTERS-analyzed quantitatively in min utes. With new DEGS Column at 180°C methyl arachidonate is reached within 30 minutes. TALL OIL METHYL ESTERS-well resolved on 10 foot EGS at 200°C. Fatty acid and Resin acid methyl esters are quantitatively determined. FUSEL OILS—are ideally separated on a glycerol column. The amazing separation of active and isoamyl alcohol is easily accomplished. INSECTICIDES —rapidly analyzed in microgram quantities on silicone column at 250"C. PARAFFIN WAX —rapidly and quantitatively analyzed on silicone columns at 295°C. C-35 reached in 65 minutes. CITRUS OILS, MINT OILS-and other essential oils are efficiently separated on 20 foot Craig polyester column. CO, MIXED WITH OTHER GASES-C0 2 , 0,, N2, CH„ CO are analyzed in less than 6 minutes. SUGARS —as methoxy methyl glycosides quantitatively deter mined with Craig polyester. Alpha and beta forms are easily separated. AMINES AND AMINO ALCOHOLS-aqueous amine solutions di rectly analyzed with minimum tailing with stationary phase on Fluoropak. Details on these a n d other a n a l y t i c a l procedures a p p e a r in A e r o g r a p h Research Notes. Request y o u r f r e £ sub scription a n d send us y o u r sample f o r f r e e analysis.
Wilkens P.O. Box 313
Dept.
é
INSTRUMENT & RESEARCH,INC.
· W a l n u t Creek, Calif.
· YEllowstone
Circle No. 73 on Readers' Service Card 34 A
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ANALYTICAL CHEMISTRY
5-1469
The vacuum system provides vacuum up to l(h 5 mm. of mercury. Pumping time is 8 minutes for the total column or 45 seconds after using the airlock for sample changes. A vacuum reservoir is available to back up the oil diffusion pump for periods up to 1 hour. The x-rays emerging through a port inclined at an angle of 20° to the surface of the specimen strike a curved analyzing crystal in the x-ray spectrometer. Crystals used are lithium fluoride for atomic numbers 20 to 92 and gypsum for atomic numbers 12 to 19. The crystals can be rotated relative to the incident x-ray beam and set to the correct Bragg angle for reflecting the characteristic emission of a chosen element through the window of a proportional counter. The signal from the counter is amplified and used to modulate the inten sity of a beam scanning the long-persistence screen of one of two similar cathode ray tubes. The beam scanning the other cathode ray tube is modulated by an amplified signal from a photomultiplier. The beam of electrons scanning the samples and the beam scanning the cathode ray tubes are synchronized so that there is an exact correlation between the area scanned on the surface of the specimen and the x-ray and electron images. The electron image is similar to the optical image and the x-ray image shows the distribution and approximate concentration of a selected element. For quantitative analysis, the monochromatic x-ray signal is passed through a ratemeter and is recorded. Resulting curves are compared with those of pure samples.
