evaluation of the fading characteristics. We found tha t the fade resistance of felt-tip recordings was comparable to, or bet ter than, tha t of the capillary pen recording inks in this particular application.

As for fineness of the line for the resolution of sharp absorption bands, small shoulders and close doublets, we have found tha t the line width produced by felt-tip pens is sufficient and tha t the tips did not deform appreciably even after recording more than 400 spectra.

After the felt-tip pens are no longer considered usable for recording, they can, generally, still be used for other purposes such as marking identifying data on the spectra (i.e., sample, date, scan speed, etc.)

The capillary feed type pens sometimes require storage in a moist atmosphere (jar or plastic container containing a small amount of water) to keep them in proper working condition along with an ever-present fine wire for unclogging. They are also subject to possible ink spillage during periodic cleaning and re- filling.

The felt-tip pens require no cleaning and need only be recapped when not in use for an extended period of t ime (more than 3 to 4 h).

For reproduction work such as required for publica- tions, we have found tha t a black, medium, or wide line felt-tip pen yields good prints even when the spectra (and the line widths) are reduced down to 25 % of the original size.

In general, we have used felt-tipped pens for more than a year on recording infrared spectrometers and have found them to be extremely satisfactory.

The pen holder adaptor for felt-tip pens could be modified to various forms to fit almost any chart recording spectrometer.

A C K N O W L E D G M E N T

The skillful assistance of S. S. DeBala in the mechan- ical design of the adaptor is gratefully acknowledged.

T r a c e M e t a l s A n a l y s i s o n S m a l l O i l S a m p l e s

Har ry P. Woods

Texaco, Inc., Richmond, Virginia 23~3~

(Received 12 February 1973; revision received 18 June 1973).

INDEX HEADINGS: Emission spectroscopy; Techniques; Trace metal analysis.

The use of direct reading emission spectrographs is a well known means of analyzing used crankcase oils for trace metals. The analysis can be accomplished without any sample preparat ion by employing a rotat ing graph- ite disc as one of the electrodes. A graphite rod is used as the counterelectrode. The disc, as it rotates, is par- tially immersed in the sample, and thus a fresh supply of oil is continuously presented to the discharge gap.

With proper calibration, this technique can be ap- plied to the analysis of m a n y types of oil. However, in m a n y cases, insufficient sample is available for even the modest needs (2 to 6 ml) of a typical sample con- tainer. We have obtained satisfactory results with only 0.5 ml of oil using a plastic cup 1 as a sample holder. The capacity of this plastic container is approximately 3 ml; however, the container is part ial ly filled with deionized water, and then the oil sample is floated on top of the water. Since the disc acts as a rotat ing skimmer, immersion of the disc to less than 1 m m is all t ha t is needed for adequate sampling. This technique permits tests to be run routinely without modification to ins t rument or sample container.

Comparat ive results on several types of lubricating oils are given in Table I.

A similar technique could possibly be employed in the analysis of oils involving questions of environmental pollution, where after extensive concentration only a limited amount of sample may be available.

Obviously, oils with specific gravities greater than one or water-soluble metal compounds in oils would have to be analyzed by other methods.

1. For example, an 8X "Caplug" plastic protector manufac_ tured by Caplugs Division of Protective Closures Company, Inc.

TABLE I. Trace metals in used lubricating oils.

Sample 1: used motor oil from diesel engine ~

Oil only Oil on water

Sample 2: used motor oil from transmission b

Sample 3 : used gear oil from differential b

Oil only Oil in water Oil only Oil on water

Iron (ppm) 54.5 ± 1.6 55.6 ~ 0.6 Lead (ppm) 6.5 ::t= 0.2 6.6 ± 0.2 Copper (ppm) 16.0 ± 0.1 15.5 ± 0.2 Silicon (ppm) 6.7 5= 0.1 6.6 ::t= 0.1 Aluminum (ppm) 2.8 ::t= 0.1 2.8 ± 0.1 Chromium (ppm) 7.7 ::i:: 0.2 7.8 ::t= 0.7 Boron (ppm) 14.1 ± 0.4 14.1 ± 0.3

180.6 ~ 6.7 178.4 ± 5.7 357.4 ± 8.9 363.6 ± 21.7 10.0 ± 0.4 10.7 ~ 1.5 4.4 ± 0.4 5.4 ± 1.2 61.3 ~ 1.8 62.1 ± 1.0 9.4 ± 0.3 9.6 ± 0.3

137.4 ± 5.1 140.0 =t: 3.7 3.7 ± 1.6 3.8 ~ 1.2 5.9 ± 0.2 6.4 ~ 0.7 Nil Nil

Nil Nil 1.1 ± 0.2 1.4 ::t= 0.3 Nil Nil Nil Nil

Average of three runs. b Average of four runs.

490 Volume 27, Number 6, 1973 APPLIED SPECTROSCOPY