fied Kjeldahl using hydrofluoric acid to w i s t the Kjeldahl attack, but such a determination takea about 3 hours. The authors have developed a method for determining the quantity of aminosilane on substrates treated with Type 2 compound. This method, like the Kjeldahl, relies on a total nitrogen determination but is much faster. The sample is fused with dry potassium hydroxide; the nitrogen is liberated as ammonia, which is adsorbed in a boric acid solution and subsequently titrated. A determination can be completed in about 70 minutes. This method has not given satisfactory results for Type 3 aminosilanes.
tube in the boric acid. Shield the upper part of the tube from radiated heat with an asbestos colla which should lie on top of the pot furnace. During 20 minutes, gradually increase the temperature of the pot furnace to about 500’ C., at which point the potsasium bydroxide reacte vigorously with the sample. If the rubber stopper becomes hot, direct a jet of compressed air on the glass a t that point. If the boric acid solution gets hot, immerse the flask in a beaker of ice water. After about 30 minutes, titrate the ammonium borate in the Erlenmeyer receiver with 0.01N hydrochloric acid, keeping the system connected. Continue the heating-purgingdistiliing o y eration. If the reaction has not been carried to completion, more ammonia will come over and turn the indicator in the boric acid yellow again. In any case, the operation should be complete in an additional 20 minutes. Indicated prccision and accuracy are within 10%.
PROCEDURE
Weigh accurately a 1- to %gram representative sample into a J. Lawrence Smith nickel crucible and cover with about 3 grams of dry potassium hydroxide pellets. Place the crucible in a Vycor tube and assemble as shown in the diagram. Mount the assembly on a ring stand with the lower two thirds of the Vycor tube in a pot furnace connected to a variable transformer. Connect the exit end of thc Kjeldahl
connecting bulb to a glass delivery tube dipped into a 250-ml. Erlenmeyer flask containing 50 ml. of 0.3% boric acid solution and 3 drops of methyl red indicator. Connect the inlet tube to a nitrogen (or argon) cylinder and adjust the flow of gaa 80 that about one bubble per second come8 through the delivery
LITERATURE CITED
(1) McHard, J. A., Servais, P. C., Clark, H. A.,ANAL.CHEM.20,325-8 (1948). (2) Pet,ty, G.M., Ibid., 28, 250J1956). (3) Rochow, E. G., “Introduction to the Chemistry of the Silicones,” 2nd ed., Wiley, New York, 1951.
Simplified Nitrometer for Use in the Dumas Nitrogen Determination David M. Miller and
R. A.
Lather, Pesticide Research Institute, University Sub P.
nitrometer described requires no valve of any sort a t the top of the measuring tube and is therefore simpler and less expensive than any others previously described. The basic design and dimensions are the same as the standard model [Steyermark, A., Alber, H. K., Aluise, V. A., Huffman, E. W . D., Kuck, J. A., Moran, J. ,J., Willits, C. O., ANAL. CHEM.21, 1555 (1949)l \\ ith two exceptions. THE
Thc tube by which thebotassium Iydroxide solution entcrs the nitromoter from the leveling bulb is placed at the back of the apparatus a t A , in the diagram. 2. The calibrated tube, instead of tmninating a t the top end, B, narrows down from a diameter of 3.3 to 3.6 r i m . to I nim., then after going through a 180” bend and opening up to its original diameter again a t D, continues down to near the bottom of the apparatus where it is terminated a t E following another 180Obend. The flares a t both B and D should be smooth, uniform, and about 5 mm. long. The zero mark of the calibrations is placed just a t the top of flare B. The nitrometer is prepared for us‘e by attaching a leveling bulb to A and connecting L and E by a length of rubber tubing, G (preferably pressure tubiug 1/8 inch in inside diameter with about 1/8-inch wall thickness). The apparatus is then supported in such a
way that screw clamps P and H fixed to the wooden block, J , may be brought to bear on G. With both screw clamps open, mercury is introduced into the apparatus in the usual way and the 50% potassium hydroxide solution in the leveling bulb is allowed to fill the nitrometer up to reservoir L. ScrewC
I
1.
1926
ANALYTICAL CHEMISTRY
D-
- B
O., London, Ontario, Canada clamp H is then closed and the nitrometer is ready to receive nitrogen. During a determination, bubbles of nitrogen rise through the potassium hydroxide solution and collect a t C. When all the nitrogen has passed into the nitrometer, the leveling bulb is raised above the level of L , and H is released, allowing the solution to flow towards L. This sweeps all the gas into the wider part of the tube below D where the individual bubbles unite to form a single large bubble (any bubbles refusing to coalesce can be made to do so by heating them gently with a small flame). Lowering the leveling bulb reverses the flow and brings the gas bubble back into the calibrated tube. This movement is stopped by closing H when the upper meniscus of the bubble reaches a point just above B . Compressing G by means of clamp F forces the bubble further downward and allows accurate adjustment of the position of the upper meniscus, so that it may be brought just to the zero mark of the scale. The level of liquid in tho leveling bulb is made to correspond with the lower meniscus of the bubble and the apparatus is left 15 minutes, following which the position of the upper meniscus is readjusted to zero if necessary, the lower meniscus is read against the scale calibrations, and the usual corrections are applied to give the true volume of nitrogen a t S.T.P. Raising the leveling bulb and opening H allow the nitrogen to be
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,
