swept out of the apparatus in preparation for a new determination. Excess solution entering L is camed off via overflow tube K . The constriction, B, at the top of the calibrated tube prevents the bubble from rising, so that potaasium hydroxide solution is properly drained from the walls of the tube. Because the c r o w sectional area of the tube at the zero mark is only about one tenth that of the calibrated portion, the zero adjustment is extremely accurate and reproducible. Nitrometers are usually calibrated by introducing measured volumes of mercury into the inverted apparatus and noting the position of the meniscus in relation to the scale graduations. In a tube of the diameter usually em-
ployed as the graduated portion, the mercury meniscus is somewhat flsttened, while the nitrogen bubble in potaasium hydroxide solution forms a hemispherical meniscus. The resulting ditrerence in volume neceasitates a correction of -0.001 ml. applied to all mercury readings. I n the present a p paratus two menisci are formed by the nitrogen bubble. However, the correction is still -0.001 ml., because the upper meniscus occurs in a narrower tube where shape differences are negligible. The apparatus is best calibrated by attaching a calibrated micrometer syringe (or micropipet) to E with the nitrometer inverted and filling the syringe and tube E B with mercury. A
measured quantity of mercury is then forced from the syringe into the mtrometer and readings are taken on the position of the meniscus in the calibrated tube. This is repeated over the full length of the nitrometer scale, so that with application of the meniscus correction an accurate calibration curve or table for the instrument is obtained. ACKNOWLEDGMENT
The authors thank A. D. Bongart and M. D. Maslak for technical assistance in the development of this apparatus. PRESENTEDin art a t the 41st Annual Conference of t i e Chemical Institute of Canada, Toronto, May 27, 1958.
Novel Micro and Semimicro Pelleting Technique for Infrared Spectroscopy Frank Bissett, Aaron L. Bluhm, and Louis Long, Jr., Pioneering Research Division, U. S. Army Quartermaster Research & Engineering Center, Natick, Mass.
the development of the potassium bromide pelleting technique in infrared spectroscopy, a variety of dies, each of which produces one specific size of potassium bromide pellet, have become commercially available or been described in the literature, Various reports have established the usefulness of these pellets in sizes varying from micro through macro [White,
