ANALYTICAL EDITION
468
is plotted against per cent distilled in the usual way. However, when the boiling point spread between, say, 0 and 50 per cent distilled is obtained in this apparatus and plotted against per cent distilled, it is much easier to detect inflections or plateaus indicating the presence of a large proportion of substances of certain boiling ranges. Again, the materials having the narrowest boiling ranges are the purest (granting no constant-boiling mixtures), for the boiling- range - of a pure substance with this apparatus is zero. It is very easy and entirely feasible to use this type of boiling point apparatus to calibrate thermocouples or thermometers (4). Vapor pressures can be conveniently measured with this type of apparatus by using it in conjunction with a suitable ballast tank and manometer or barometer. Molecular weights by the method of boiling point elevation are obtained by using either one or two sets of apparatus. For this purpose the liquid withdrawal ring and side tube should be eliminated. The vapor volume compared with the -liquid volume can be kept negligibly smail, and the
Vol. 6, No. 6
hold-up of condensed liquid is also small, so the enrichment of the liquid being boiled is slight or of negligible effect. Using two apparatus and simultaneously boiling pure solvent in one and the mixture of solvent and substance whose molecular weight is desired in the other, corrections for variation in barometric pressure are avoided.
LITERATURECITED 41,721 (1919). (1) Cottrell, F. G., J.Am. Chem. SOC., (2) Davis, H.L.,J. Chem. Education,10,47(1933). (3) Davison, A. W.,and van Klooster, H. S., “Laboratory Manual of Physical Chemistry,” 2nd ed., p. 68, John Wiley & Sons, N.Y.,1931. (4) DeVries, T., IND. ENQ.CHEM.,19,1311 (1927). (5) Gordon, H.B., J. Chem. Education,10,489(1933). (6) Reilly, J., and Rae, W. N., “Physioo-Chemioal Methods,” pp, 427-37,Znd ed., D.Van Nostrand Co., N. Y., 1932. (7) Sherrill, M. S., “A Course of Laboratory Experiments on PhysicoChemical Principles,”p. 80, Macmillan Co., N. Y., 1924. Bull.SOC. chim. France, 49,Pt. 2, 1563 (1931). (8) Svietoslawski, W., J . Am. Chem. SOC.,41,721 (1919). (9) Washburn, E. W., RBCEIVED J ~ 9, I1934. ~
Apparatus for Melting Point and Microboiling Point *
WILLIAM L. WALSH Research Laboratory of Organic Chemistry, Massachusetts Institute of Technology, Cambridge, Mass.
T
HE apparatus shown in Figures 1and 2 has been in constant use by a large number of students for over a year
and its success seems to warrant a description. To the usual conveniences attending the use of a copper block it adds the important advantages of better visibility and temperature control. The former is secured through the use of a lowpower microscope and a direct light source, the latter through convenient means of heating the block or cooling it by a stream of water. An additional advantage is the possibility of determining boiln ing points of liquids using v e r y s m a l l quantities of material. As shown in Figure 1, the apparatus consists of a copper block, A , fixed in such a position that a removable 50power microscope, B, may be focused by means of an adjustable shield on t h e meltin point t u b e throu the horizontal hofe in the block. Illumination is provided by a 40-watt lamp, C, which produces no b l i n d i n g effect on the eye of the observer, because of the small amount of light that enters the hole in the block and the artial blocking of t i e latter by the filled c a p i l l a r y tube. The material
should not be packed solidly in the melting point capillar but lightly distributed by vibratin the tube with a file. S d c i e n t light is thus allowed through tRe substance to facilitate observation prior to melting. In the construction of the block the general directions of Friedel (2) may be followed, but it is recommended that a 0.125inch hole be substituted for the prescribed slot which is difficult and time-consuming to make. This modification has been found to give excellent results. The block is heated by the microburner, D,fastened to the sliding plate, E, and connected by rubber tubin with the needle valve, F. By means of the rod, G (Fi ure 2), t%e burner can be pushed forward under the block for feating or withdrawn for cooling, as indicated by the dotted lines. The burner is li hted by pressing the momentary contact switch, H, in series wit\ the &volt transformer, I , which supplies current to the ignition coil, J. From this coil one wire leads to the base of the burner, the other to a copper strip, K, extending just over the top of the burner when rod G is withdrawn. The spark which results when switch H i s pressed is sufficient t o light the burner. Switch L controls both the lamp and the transformer. Cooling the block is accomplished by a fine stream of water directed at its base from a brass tube enclosed by the co per cup, M , which is fixed in such a position on the sliding plate, that it is directly under the block when rod G is withdrawn. The enclosed tube is connected by rubber tubing to a supply bottle in an elevated osition from which a stream of cold water can be directed on t\e block by turning a stopcock. A second tube in the bottom of the cup serves to carry off excess water. The apparatus is enclosed in a wooden cabinet, shielded, for safety, in the vicinity of the block with asbestos paper. The top is made of heavy sheet iron perforated with 0.25-inch holes to allow escape of hot * a i r a n d provided with a suitably sized hole in which t h e copper block is inFIGURE 2. REAR VIEW serted.
E,
FIGURE 1. SIDEVIEW
November 15,1934
I N D USTR I A L AN D EN G I N EER I N G CH EM I STR Y
Any fogging of the microscope lens due to water vapor resulting from the use of the cooling device may be easily remedied by withdrawing the microscope from its shield, drying, and replacing in position, but this procedure is unnecessary when the temperature of the block is above 100" C. The device is particularly useful in the case of high-melting compounds. The block may be heated quickly to within 10" of the melting point, the burner removed by withdrawing the rod, and a stream of water allowed to play on the bottom of the block for a n instant. The rapid rise in temperature is thus brought to an abrupt halt within less than a degree. The burner may then be replaced, using a small flame so that the melting point of the compound is slowly approached. The device is also valuable in cooling the block rapidly when the melting point of a second and possibly lower-melting compound is to be determined at once. This feature is important if the apparatus is to be used by a large number of students. Among other advantages in the use of the apparatus are: absolute safety from accidents sometimes accompanying the use of sulfuric acid baths; extreme accuracy as regards softening point, sintering, change in color or crystalline form, and melting point range of compounds; the possibility of taking higher melting points; and the use of smaller samples. This last advantage is noteworthy in the determination of boiling points by a modified Siwoloboff (3) method. For this purpose a large capillary tube is used as a container for a fraction of a drop of liquid and a fine capillary tube, sealed in the middle, is introduced. The former is then inserted in the
469
block as for a melting point determination and the same procedure is followed m in the ordinary Siwoloboff method. In Table I are given the melting points of some pure compounds observed by the use of this apparatus and by the usual sulfuric acid bath method. TABLE I. COMPARISON OF RESULTS MELT IN^ POINT
COMPOUND
By apparatus described
c.
By usual apparatus
c.
Cinnamyl alcohol 27-29 27-29 p-Nitrotoluene 51-52 51.6-52 Naphthalene 79-80 79-80 Benzoquinone 111-113 111-113 Benzoic acid 120-121 120-121 189-190 188.5-190 Succinic acid Diphenic acid 227-228 227-228 274-276 Anthraquinone 274-275 3-Aminophthalhydrazide 324-325 324-325O a Melting point taken by means of a copper block of the Berl and Kuhlman type ( 1 ) .
ACKNOWLEDGMENT Grateful acknowledgment is made to A. A, Morton of this laboratory for his interest in the construction of this apparatus and his assistance in the preparation of this paper.
LITERATURE CITED (1) Berl and Kuhlman, Ber., 60, 811 (1927). (2) Friedel, Bio&m. Z . , 209, 85 (1929). (3) Siwoloboff, Ber.,19,795 (1886). RECH~IVED June 16, 1934.
A Converted Air-Pump Shaker AVERYA. MORTON, Massachusetts Institute of Technology, Cambridge, Mass. OR laboratories which are supplied with compressed air simple shaking machine can be constructed from an
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air Pump, a set of door springs, and a suitable frame and platform. The general principle involved is the use of compressed air to drive the shaker forward, the release of the air pressure when the piston passes some holes bored in the barrel of the pump, and the return of the piston to its initial position as the result of the tension imposed upon the springs in the forward stroke, The construction in use in this laboratory, in which an air pressure Of lo pounds is maintained at the source, ifi illustrated in Figure 1.
which are mounted either on adjustable metal stands or wooden blocks so that the barrel is in line with the shaker latform. A set of door springs, 8,which are 0.44 incg in diameter X 12 inches (1.1 x 31 cm.) long [their osition is such as to make an 8 x 12 inch (20 x 31 cm.) rectan ye] are held between the top of a frame, F, and the base, B. dnly slight tension is needed. ~
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screw, since the latter has a tendency to work loose. The shaking platform is made and attached as follows: Between the front and rear pairs of springs two brass rods, threaded on each end and fitted with 0.625-inch (1.6-cm.) pipe holders, are attached. To secure a good grip a rubber stopper, bored to fit snugly, is first slipped over each s ring so that the ipe clamp is pulled down upon the rubber. T i e author's attacfment was An 18 X 1.75 inch (46 X 4.5 cm.) automobile hand air pump, made 3.75 inches (9.5 cm.) from the lower end of the spring. P, is altered as follows: The handle. is removed, a, and the end of It is obvious that a longer stroke is secured if the attachment is made near the center of the the rod is threaded and fitted spring, b u t because of t h e with a bearing connecting to nature of the frame used it was the shaking p l a t f o r m . The impossible to make a perfect cap is removed, b, to reduce adjustment at this point. A friction and noise. Four 0.19board is next mounted on these i n c h (0.5-cm.) holes, c, are brass cross pieces by means of drilled in the barrel at 90' intervals in a line a r o u n d the U-fasteners or screws. Connection is made to the piston circumference 8.5 inches (22 rod of the ump as indicated cm.) from the bottom end of the before. A !ox or other suitpum . The size of the holes able receptacle may then be is of? more importance t h a n the osition because the leather fastened on t h e p l a t f o r m . The frame is made from 0.75wasEer of the piston will catch inch (1.9-cm.) c h a n n e l iron in an opening that is too large. bent into the shape indicated The air valve a t the bottom is inFigure 1 and made rigid removed and the hole bored out to 0.25-inch (6.4-cm.) size, b y cross pieces. The whole a p p a r a t u s is mounted on in order to admit air rapidly a wooden base, 40 X 12 X to the cylinder. The recon1.75 inches (101 X 31 X 4.4 structed ump is held in place by two Erge pipe clamps, C, FIGURE 1 cm.)
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