Pressure Regulator for Us of Carbon an M. F. FURTER AND A Hoffmann-La Roche i A new- pressure regulator for u s e in the m i c m d e t e r m i n a t i o n of carbon a n d hydrogen is described which is helieved to have distinct advantages over the Pregl typo.
A.
LTHOUGH the Pregl (6)type of regulator is used generally in the microdetemination of carbon and hydrogen, it has certain disadvantages. The prongs which hold the attachfible inner tube in place &e subjected t o the corrosive action of the solution used and the life of the regulator is greatly shortened. Likewise, there is no attached scale t o aid in making the settings. Substitutes (f-4,6, 7) for the Pregl regulator have been offered but none hs received wide aoceptance. The pressure regulator described bere has proved excellent over a number of years (in approximately five years' use by M. F. Furter a t the Federal Institute of Technology in Zurich and at F. Hoffrnsnn-La. Roche & Company, Ltd., Bade, Switzerland, and in six years' use of five units by AI Steyermark in these lahoratories). It has an attached scale and contains no metal parts that are subject t o & tack by mid or alkali. The rubber connecting tube is the only part t.hat, necds replacing after several years of use.
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I1 IC
U
e
Figure 2.
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Diagram of U n i t
height, connected by means of rubber tubing. Whore only oxygen is used one unit is required while setups using oxygen and air require duplicates, as show; in Figure 1. The two regulators are connected by means of a T- or Y-tube, which in turn is connected to the bubble counter of the combustion train. Five per cent solution of sodium hydroxide is used in the regulators. Figure 2 shows the details of construction of the unit. a is the
When.4he space between c and d isoompletely filled, the exiess gas overflows a t f and passes up through the solution and out into the air through h. The position of e should be such that the gas bubbles strike the notch, f. (If, on testing a regulator it is found that the outlet has been improperly placed, the condiiion may be corrected by applying the flame of a small blast lamp a t point g. When the glass has softened slightly a t g, that section of the tube between g and e is allowed to fall into place by gravity.) The height at which the solut,ion st,ands in b is shown on the
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graduated scale, this also being the pressure head maintained in d. The gaer under the desired pressure passes out through the stopcock and tube i to the bubble counter and the combustion tube. ACKNOWLEDGMENT
The authors are indebted t o G. Lissen for the drawing used and t o L. Hodax for the photograph. Both are in the employ of Hoffmann-La Roche Inc.
LITERATURE CITED (1) Friedrich, A., Mikrochemk, 10, 328 (1931).
(2) Hamill, Nr, H., ISD.ESG.CHEM., ANAL.ED., 9,365 (1937). (3) Lindner, J., Mihochemie, 20,209 (1936). (4) Lindner, J., and Wirth, W., Ber., 70, 1025 (1937). (5) Pregl, F., “Quantitative Organic Micro Analysis,” tr. by Ernest Fyleman, p. 18,London, J. & A. Churchill, 1924. (6) Riesenfeld,E.H., Chem.-Ztg., 42,10 (1018). (7) Vance, J. E., IND.ENG.CHEM.,ANAL.ED., 13, 132 (1941). RECEIVED July 12, 1947.
MICROEFFUSIOMETRY LEONARD K. NASH kfallinckrodt Chemical Laboratory, Harvard University, Cambridge, Mass.
An apparatus is described for determining the molecular weight of 0.5 cc. of permanent gas or 0.5 mg. of volatile liquid. The apparatus is easy to construct and operate, and no microweighings are involved. A single determination requires about 15 minutes, and an average error of less than 2Yo is found with single-component samples. The method has wide applicability for permanent gases and con-
T
H E identification of traces of gas unabsorbed in gas analysis systems, and of small amounts of volatile organic liquids which are occasionally isolated, presents some difficulty. A method providing rapid approximate data for the molecular weights of these specimens would yield a worth-while clue to their qualitative nature. Unfortunately, such a method is not always available. Infrared,and mass-spectrographic determinations are excellent, provided the requisite equipment is a t hand. The Edwards gas density balance (5),particularly in its microadaptations, requires some skill in its construction and operation, and it is not well suited for use with materials of relatively low volatility. Microadaptations of the Victor Meyer and Dumas methods are well known, but they necessitate an accurate microweighing and a generally r e h e d technique, and they cannot be used for determinations with permanent gases. A micromethod based on the measurement of relative rates of effusion and the use of Graham’s law appears t o present many advantages, I t is unquestionably rapid and can be made simple as far as apparatus and technique are concerned, particularly since no microweighings are involved. Furthermore, there is reason to believe that a low-pressure (micro) effusiometer may function more satisfactorily than the conventional high-pressure (macro) apparatus, other things being equal. A very considerable number of modifications of the ordinary Bunsen-Schilling type effusiometer have been described, but most of them require 100 to 200 cc. of noncondensable gas. Neither these nor a macromethod recommended for the study of condensable vapors (7) seem well suited to microadaptation. An excellent semimicroeffusiometer has been described by Kahle ( I O ) , but about 30 cc. of sample at a pressure of approximately one-third atmosphere are required. Perhaps the only true microdesigns of simple effusiometers are those of Knudsen ( 1 . 4 , which require a very delicate quartz suspension gage; and that of Debierne (e), which requires an accurately calibrated McLeod gage and is thus obviously unsuited for work with condensable vapors. A design for a microeffusiometer combining the properties of simplicity, accuracy, and wide applicability has therefore been
densable vapors. Organic liquids with boiling points up to170°C.may be used. Within experimentalerror, a strict adherence to Graham’s law is found in practically all cases. The apparatus is Shown to meet the essential criterion for the application of Graham’s law, and it is indicated that previous failures to secure satisfactory results with pinhole orifices in glass were caused by failure to meet this criterion.
sought. It should operate with small volumes and a t low pressures, in the interests of economy of material. Low pressure is further desirable in the interests of accuracy, and in order that the method may be applied successfully to materials of low vapor pressure. For the measurement of these low pressures a McLeod gage will not serve if the method is t o be applied t o condensable vapors, and most of the other low-pressure gages are unsuitable either because, like the Pirani gage, they are not absolute gages, or, like the Knudsen gage, they are fragile and expensive. A horizontal-form Huygens micromanometer (15),in a form modified for this work, was chosen as the most likely possibility. The construction of an orifice suitable for use in a microeffusiometer has probably been the main obstacle to progress along these lines. Very fine orifices in extremely thin platinum foil can be prepared (IS), but the process is not unattended by difficulties. The use of punctured collodion films (17) did not seem promising if organic materials were t o be studied. An obvious possibility, however, would be a pinhole produced by a spark discharge through a thin glass membrane. Such an orifice should be small, inexpensive, and easy to fabricate and to build into the apparatus. Despite previous reports indicating their unsuitability (9, 7 ) ,such orifices have proved satisfactory in practice. APPARATUS
A microeffusiometer meeting the specifications outlined above is shown in Figure 1. Other dispositions are possible and have been used successfully, but the one shown seems to be the most generally satisfactory.
M represents the body of the micromanometer, made from 24mm. tubing with an over-all height of 6 to 7 cm. The manometer is filled t o the level shown with distilled mercury. The space above the left branch of M communicates directly with orifice 0 and, through stopcock S, with the sampling system and the pumps. The bore of stopcock S should be a t least 2 mm. in diameter and preferably somewhat larger. The right branch of the manometer terminates in a length of heavy-walled capillary tubing of the following specifications: Sections B and D are 3-cm. lengths of 2-mm. capillary; sections C and E are 2-cm. lengths of 0.5-mm. capillary; and section F is a 6-cm. length of 2-mm. capillary, terminating in bulb G , which has a volume of
