Operation of Analytical Microbalances Highly
Sensitive to Temperature Changes FRITZ BREUERY1 Department of Chemistry, Pennsylvania State College, State College, Pa.
T
HE high degree of sensitivity attained by most analytical
to permit starting the balance to swing. During the weighing proper this case is kept closed. PROTECTION FROM EFFECTS OF MANIPULATIONS IN THE BALANCECASE. An aluminum sheet separating the beam from the lower part of the balance (pans) was kindly installed by Christian Becker, Inc., New York, and the balance floor was covered with sheet copper to dissipate local heating of the balance floor. By lengthening the rider carrier and release handles for 20 cm., the inconvenience of counterbalancing the heat radiation of the hand can be omitted.
microbalances is not infrequently impaired by their great temperature sensitivity. Some instruments are more sensitive toward temperature fluctuations than others of the same manufacture, and according to information from an experienced maker of microbalances the causes of this different behavior have not yet been traced definitely. The precautions which were found necessary to make practical weighings to j=1gamma with an extremely temperaturesensitive instrument of the long-beam type are reported in this note. They should be of general value if microanalytical weighings have to be carried out under handicap.
Manipulation of Weights and Objects to Be Weighed Ordinary crucible tongs 24 cm. long to which the ivorytipped forceps of the set of analytical weights are attached, and another pair of these tongs for boats, weighing flasks, etc., minimize heat radiations from the hands of the operator. Pregl’s carbon dioxide- and water-absorption tubes are handled by a wire fork of such length that the hands always remain well outside the balance case. With this technic it was even possible to use an often-frequented office as weighing room.
Protection of the Balance PROTECTION FROM OUTSIDEDISTURBANCES. A protective case shields the balance against drafts and heat radiating from the operator. Between weighings the side windows of the balance case are kept open and the smoothly working sash window of the protective case is raised 2 to 3 cm. to permit “acclimatization.” Five minutes after the manipulation of weights, etc., all windows are closed and after 5 more minutes the outer (protective) case is opened only long enough
*
RECEIVEDApril 9, 1937. Part of a report presented before the Division of Physical and Inorganic Chemistry, Symposium on Reoent Advances in Microchemical Analysis, at the 89th Meeting of the American Chemical Society, New York, N. Y., April 22 t o 26. 1935.
Present address, Ohio State University, Columbus, Ohio.
Modified Micro-Dumas Nitrogen Determination with Readily Available, Air-Free Carbon Dioxide FRITZ BREUER, Department of Physiology, Ohio State University, Columbus, Ohio
T
Much would be gained, particularly for the laboratory that does not specialize in microanalysis, if carbon dioxide of the required degree of purity could be provided with a minimum of preparation in an apparatus of simple construction. These requirements are fulfilled in Dumas’ original well-known technic. Pregl (9),intent upon the general applicability of his methods, discarded the idea of generating carbon dioxide from magnesite or sodium bicarbonate, be-
HE success of Pregl’s micro-Dumas nitrogen determination depends mainly on procuring carbon dioxide of exceptional purity. Various generators have been described ( I , 9, 4, 7, 8, IO), among them Poth’s apparatus (8). This has proved very satisfactory, but it is somewhat fragile and the starting operations are rather involved. Reproducible blanks have been made possible by the modification of Trautz and Niederl (11).
FIGUREl 354
JULY 15, 1937
ANALYTICAL EDITION
cause of the danger of volatilizing part of the sample by the hot carrier gas in the initial scavenging of the tube. Moreover, the highly important rate of gas flow could be secured more safely with the Kipp generator. Dubsky (S), Govaert (6),and Ide (6) have successfully applied magnesite to the micro-Dumas analysis of less volatile material. The apparatus shown in Figure 1 supplies a well-controlled flow of carbon dioxide a t room temperature. Its construction requires little skill in glass blowing.
A Pyrex test tube, preferably heavy-walled (bomb tubing), A ,
10 to 15 cm. long is attached by means of a rubber stopper t o a gasometer, such as B, of 250- t o 300-cc. capacity. A two-way stopcock, C, permits removal of air from A . Cock D takes over the functions of regulating the gas flow, the customary stopcock
between microazotometer and combustion tube thereby being eliminated. Sodium bicarbonate (analytical grade), being generally available in the laboratory, is used instead of magnesite, of which a special grade (Kahlbaum’s) is required. Mercury serves as confining liquid in the gasometer. One charge of sodium bicarbonate, packed tightly, will serve for seven to eight analyses (one day’s work). By gently heating for 2 to 3 minutes the portion of test tube A covered with wire gauge, air is expelled through C. Gasometer B is then filled with carbon dioxide. Water formed in the liberation of carbon dioxide condenses on the mercury surface and does not interfere with the determination. It is removed through C when recharging test tube A . When fiist assembling the apparatus and after it has been unused for some time, it is necessary to flush the storage vessel two t o three times with carbon dioxide, to iemove air adsorbed on the walls. Care should be taken to eliminate air ockets from the pressure tubing connecting the gasometer a n a leveling bulb. By evacuation through C, traces of air can also be removed. The combustion proper and the measuring of the nitrogen volume are carried out according to Pregl’s directions (9). Since the gases in the combustion tube are at a pressure close to atmospheric, the mercury level confining the potassium hydroxide solution in the microazotometer should extend only a few millimeters over the gas inlet tube. When starting the scavenging operation, the flame of the movable burner should hit the empty portion of the combustion tube about 1 cm. from the filling. After gas evolution in the nitrometer has ceased, stopcock D should be manipulated slowly and with great care. Results are well within 0.1 per cent (absolute) of the theoretical value. Ordinarily, no blank determination is necessary. When not in use, the gasometer remains filled with mercury, both stopcocks being closed. The method described in this paper has been in use for some time in this and in another laboratory.
355
A Macro- or Micro-Gooch Filter RALPH E. DUNBAR, Iowa State College, Ames, Iowa
A
SMALL Gooch funnel can be readily fashioned from two sizes of laboratorv glass tubing. as shown, and is particularly convenient for determining halogens by indirect methods (2). Other uses, where small precipitates are handled quantitatively, will suggest themselves. It combines the essential features of the usual Gooch crucible, supporting funnel, and connecting rubber tubing, and is prepared and used like any typical Gooch filter. The smaller size of tubing should be about 6 or 8 mm., to enter readily the openings of ordinary rubber stoppers, and the larger size will depend upon the probable uses of the funnel. A solid, round glass bead will serve as a loose support for the asbestos fibers, which are added in the usual manner. The prepared funnel can be most conveniently heated in an electric oven or electric or gas micromuffle (1). After the c o m b i n e d silver halides are weighed. the funnel mav be placed in a heated tube.’ A slow s t r e a i of chlorine passed through the tube displaces the bromine or iodine present. 1
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Literature Cited (1) Pregl, ‘.‘Quantitative Organic Microanalysis,” 2nd ed., tr. by E. Fyleman, p. 165, Philadelphia, P. Blakiston’s Son & Co., 1930. (2) Treadwell-Hall, “Analytical Chemistry,” Vol. 11, Quantitative Analysis, 7th ed., p. 299, New York, John Wiley & Sons, 1928.
RECEIVED June 10, 1937.
A Manometer for Carbon and Hydrogen Pressure Regulation WILLIAM H. HAMILL Fordham University, New York, N. Y.
Summary
A simple carbon dioxide generator is described which promptly supplies gas of the required purity. Pregl’s apparatus is further simplified by placing the precision stopcock between combustion tube and generator.
Literature Cited (1) Allen, C. F. H., and Young, D. M., Can. J . Research, 14, 216 (1936). (2) Clark, E. P., J . Assoc. Oficial Agr. Chem., 16, 575 (1933). (3) Dubsky, J. V., “Vereinfachte quantitative Mikroelementaranalyse organischer Substanzen,” Leipzig, Veit & Co., 1917. (4) Friedrich, A., Mikrochemie, 10, 355 (1931). (5) Govaert, F., Ibid., 9, 338 (1931). (6) Ide, W. S., IXD. EXG.CHEM.,Anal. Ed., 8, 56 (1936). (7) Lowe, E . W., and Gutmann, W. S., Ibid., 4, 440 (1932). (8) Poth, E. G., Ibid., 2, 250 (1930); 3, 202 (1931). (9) Pregl, F.,“Quantitative Organic Microanalysis,’’ 2nd ed., pp. 94, 102, Philadelphia, P. Blakiston’s Son & Co., 1930. (10) Rutgers, J. J., Compt. rend., 193, 61 (1931). (11) Trautz, 0. R., and Niederl, J. B., IND.ENG. CHEW,Anal. Ed., 3, 151 (1931). RECEIVED April 9, 1937. Presented before the Microchemical Section at the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 t o 11, 1936. Carried out under a grant of the Rockefeller Foundation administered by F. A. Hartman.
THE
maintenance of correct pressure relations in the microdetermination of carbon and hydrogen is facilitated by the introduction of a simple water manometer between the carbon dioxide absorption tube and the Mariotte flask. The addition of a drop of ink to the water assists in reading; a small bulb precludes the possibility of sucking water into the gas line. The rate of gas flow may be adjusted in the usual manner or with the temporary assistance of a second m a n o m e t e r a t the junction of the combustion tube and the water absorption tube, the pressure regulator and the Mariotte flask being so adj u s t e d as to maintain atmospheric pressure a t this junction. The proper difference in water levels is marked on the first manometer and this diff e r e n c e is maintained during subsequent runs. RECEIVED May 19, 1937.
