. ANALYTICAL CHEMISTRY
1940 The construction of the atomizer is shown in Figure 1.
A bulb, A , is blown on the end of a piece of 3-mm. borosilicate glass tubing. The tubing is cut about 1.5 inches below the bulb, and the cut end is lightly fire-polished. The bulb is sealed into a piece of 9-mm. tubing, B, and a bulge, C, is blown in the larger tubing just below the ring seal. While the seal is still plastic, the tubing is manipulated so that the inner and outer tubes are concentric; the assembly is allowed to cool and the outer tube is constricted, D, leaving a clearance of about 1 mm. between the inner and outer tubes.
several occasions. Without a safety switch to shut off the heating current to the pump, there existed the danger of distilling out large quantities of mercury. With water-cooled, oil diffusion pumps, there is the additional danger of pyrolysis of the oil. h switch of this type would also be useful on distillation or reflux apparatus. The control element consists of a double-ply brass bellows, A (supplied by The Robertshaw Fulton Co., Fulton Sylphon Division, Knoxville, Tenn.) having twelve corrugations, outside diameter of 1.5 inches, and an over-all length of 2 inches, in each inch end of which has been soldered a circular brass plate, B , thick. The top plate has a counterbored hole 1/1 inch in diameter drilled through its center, into which a 2-inch length of copper tubing 3 / b inch in outside diameter has been soldered. In like manner, the bottom plate has a 1/8-inch hole a t its center and a copper tube ’/4 inch in outside diameter leading from it. The upper tube is clamped to a rigid support. A Type W, lever arm microswitch, C, with contacts rated at 15 amperes a t 125 volts, is clamped to a vertical rod and mounted so that the end of the lever arm is below the bottom plate of the bellows. The switch is connected in series with the heater to be controlled, D, and the voltage source, E. A rubber tubing connection is made between the cooling water outlet from the apparatus and the 3/8-in~h tube a t the top of the bellows. The 1/4-inchtube at the bottom of the bellows is led to a drain.
A
B Figure 1
9 side arm for the air hose, E, of 7-mm. tubing, is now attached, and a hole about 5 mm. in diameter is blown in the bulb, F . The liquid feed tube, G, is prepared as shown from capillary tubing 2 mm. in inside diameter and sealed to F as shown. Finally, a control hole, H , 5 mm. or larger in diameter, is blown in the top of the bulge, and the outer tube is cut off and ground down to be flush with the end of the inner tube. Inner and outer tubes of the atomizer jet are now made concentric by warming in a flame and adjusting as needed, and the assembly is annealed. If the clearance between inner and outer tubes is found to be too large, it can be reduced by careful fire-polishing. The atomizer is usually used by fixing the fluid feed tube in a two-hole rubber stopper, so that the fluid feed reaches nearly to the bottom of a 250-ml. Erlenmeyer flask; if desired, the liquid feed can be ring-sealed through a ground-glass cap for a flask or bottle to give an all-glass system. LITERATURE CITED
(1) Berry, H. K., “Quantitative Estimation of Urea by Paper Chromatographic Methods with Appliration to Human Urine,” Univ. Texas Pub. 5109 (1951). (2) Morris, R. T., ANAL.&EM., 24, 1528 (1952).
Safety Switch for Water-cooled Systems. Walter Roth, Ff7alker Laboratory, Rensselaer Polytechnic Institute, Troy, K. Y. safety E switch has been designed for use with any electrically heated apparatus which requires circulation of cooling water. It is being used successfully in this laboratory as a safety control on a water-cooled, mercury diffusion pump which operates unattended through the night. For some unknown reason, water pressure has fallen off during the night on ~
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When ivater is flowing through the apparatus, the bellows expands as a result of the flow restriction oft’ered by the smaller outlet tube. The height of the microswitch is adjuste&so that the skyitch is depressed to the on position when the desired rate of coolant flow is obtained. A decrease in the rate of flow causes the bellows to contract toward its normal position and results in the interruption of the heating circuit. The microswitch height can be adjusted to give cut-off at any desired flow or at complete cessation of flow. The use of a similar type oi instrument i n conjunction with a pi essure-protective circuit for vacuum systems has been described [Amdur, I., Rev. Sci. Inatr., 18, 60 (1947)l. Vapor Pressure Ebulliometer for Milliliter Samples. Sam R. Hoover, Harry John, and Edm-ard F. XIellon, Eastern Itegional Research Laboratory, Philadelphia 18, Pa. I x STUDIES of the separation of amino acids by distillation of the
.\7-acetyl amino acid esters, the determination of the boiling point-vapor pressure relationship of a number of samples was required. Measurements on small samples ( < 2 ml.) at temperatures of 75’ to 250’ C. and pressures of 2 to 100 mm. were the essential conditions which had to be met. -4survey of the literature revealed no technique that fulfilled these requirements. -4fter numerous unsuccessful attempts to employ the micro-
/ 1941
V O L U M E 25, N O . 12, D E C E M B E R 1 9 5 3 method of Garcia (f),the apparatus shown in Figure 1 was developed. It is a simple adaptation of the Cottrell principle. The larger and more elaborate apparatus described by Willingham et al. ( 6 ) undouhtedly can he used to produce results of great accuracy in the characterization of organic compounds available in quantity. Willard and Crabtree have described a Cottrentype appmatus which more olosely approaches the present design than others, but its use a t reduced pressures was not reported ( 6 ) . Ebulliametric measurements and vapor-pressure tensimeter stills have been reviewed recently (4). APPARATUS AND METHOD
The boiling pot and column are of 15-mm. borosilicate glass tuhina. The reflux bell is about 35 mm. in diameter. The reflux
capric acid with the data ohtaincd on larger samples by Pool and Rakton (e). A log P versu8 1/T plot of the results is ebown in Figure 2. The line was obtained as the least square straight line, using all the points obtained by use of the new ebulliometer. Its equation is log P = 10.3002 - 3937/T; 95% of the observed pressures fell within 4% of the pressure values given by the curve. The corresponding equation cdculated from the data of Pool and Ralston is log P = 10.3719 - 3970/T; 95% of their observed pressures fell within 9% of the pressure values given by the least sqnme line for their data. Both sets of data are in excellent agreement. The slight difference in slopes and the better precision of the new data itre probably due to the larger number of data obtained in this study and to the better control of pressure b y modern pressure regulators.
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a funnel placed underneath. The tungsten wire projects through a sheet of asbestos paper which is supported immediately below the app a r a t u s . T h i s wire is heated by 8. microburuer,
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photograph) on the end. The 10130 standard-taper borosilicate glass joint takes a commercial 125-nun. immersion thermometer. The only oritioel dimension is that which places the thermometer bulb just below the lip of the boiling pot. A 10- to 15-mm. length of 0.5-mm. tungsten wire is sealed through the bottom of the pot,. The comuleted apuazatus should be thoroughly annealed. Apparatus i s supported by a clamp around the rubber tubing of the vatuum line on the side arm. The lower portion of the side arm serves as a receiver and the upward sloping portion serves as B condenser. A stream of water is run onto a cloth which is
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4UlHORs' D4T4 O A T 4 OF POOL'&
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Figure 2. 0
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R4LSTON
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104
Yapor Pressure of Capric Acid Authors' data Data of Pool and Ralston
of aibbezos around the av
parat& (s o p e k e d in an air-conditioned or drafty Figure 1. SemimicmThe sample is added to ebulliometer the pot to a depth of about 10 mm. It should not touch the thermometer bulb even after exuausian on heating. Silicone stopcock grease on the thermometer joint is used t i lessen the possibility of oantaminating the sample. The system is DumDed down t o the reauired vacuum. which is maintained b y manostat. The minostat describkd by Ratihfird and Fein ( 5 ) was used successfully t o control the pressure, which was measured by a Zimmerli gage (7) to 0.1 mm. A series of determinations a t increasing pressures is made. A 10- to 15-minute period in which the reflux is maintained about half-way up the tube between the bell and side arm is sufficient to establish stable
This ebulliometer has also been used to determine the vapor pressure-temperature curves of nine acetylated amino acid estcrs; 70% of the experimental values are within 3% of the values cnlculated from the equ&on for thc least squares line through the data. in the range of 2 to 100 mm. These ditta. will be described in detail a t a later date. This ebulliometer, therefore, is a simple and precise apparatus For the determination of the vapor pressures of milliliter quantities OF materials by the boiling point method a t all pressures from atmospheric downward. ACKNOWLEDGMENT
The authors are indebted to W. S. Port of this laboratory for supplying the sample of capric acid, and to M. C. Audsley for the photograph of the apparatus. LITERATURE CITED
The thermometer is easily calibrated by determining the boiling points of pure compounds which are accepted standards for thermometer calibration. This calibration can he made at atmospheric pressure. The temperatures, reported herc, vere read to 0.19 RESULTS
The ability of this ebulliometer to function a8 desired was checked by oomparing the boiling point curve of a sample of pure
(1) Garcia. C. R., IND.ENG.Cn~x.. ANAL.BD.,15, 648 (1943). (2) Pool, W. 0..md Ralston, A. W., I d . Bng. Chen., 34,1104 (1942). (3) Ratchford, W.P.,and Fein. M.L.. ANAL.CHEM.,22,838 (1950). (4) Weissberger, A,, "Physical Methods of Organic Chemistry," 2nd ed., Vol. 1, Part 1. Chaps. IV, V,New York, Interscience Publishers. 1949. (5) Willard, M.L., and Crabtree, D. E., IND.Ewe. C ~ E MANAL. .. Eo., 8, 79 (1936). (6) Willingham, C. B., Taylor, TI'. J., Pignocoo. J . M., and Rossini, F. D.. J . Reaeareh Natl. Bur. Standards,35,219 (1945). (7) Zimmerli. A,, IND.END.CHEM.,ANAL.ED..10,283 (1988).
