Robert E. Wagner
and Edwin F. Meyer' U.S. Army Coating and Chernicol Loboratory Aberdeen Proving Ground, Morylond
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A Simple and Accurate Dibtometer for Liquids
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The density of a liquid as a function of temperature may be readily measured to an accuracy of =t0.0002 g/ml using a dilatometer made from F'yrex tubing and a Teflon needle valve (see figure). It is very convenient, allowing outgassing in situ and total filling without danger of loss of material. Its volume is about 20 ml; it is calibrated with pure mercury. Its principle of operation is that of the standard dilatometric technique in which the mercury expelled upon a rise in temperature is weighed.2 In practice 3 ml of mercury (weighed) are placed in the dilatometer, and 10-15 ml of sample are placed on top of the mercury. The latter is accomplished by temporTEFLON arily replacing the Teflon needle w i t h a fine stemmed funnel whose tip reaches down past the valve seat. The weight of the sample is determined by difference. (All weights must be corrected for the presence of air in the dilatometer.) T h e d i l a t o m e t e r i$ mounted on a ring stand with a weighed reservoir of mercury situated at LDUID DiLiiTDMEER the tip of the capillary. A dilatome,er tor liqvidr Mercury is drawn into Tho needle valve is made b y Fisher & the capillary by opening Porter. The length and design of the the ~ ~valve fslightly l capillary may b s modified to fit available thermostat. and drawing on the
side arm with a rubber bulb. As soon as the siphon action of the mercury takes over, the amount entering can he controlled with the needle valve. Enough mercury must enter to fill the capillary completely. A flask of liquid nitrogen is slowly raised about the dilatometer, and air is pumped out via the side arm. If, after allowing the dilatometer to warm slowly to room temperature, an air bubble remains, the outgassing is repeated. The total mass of mercury in the dilatometer is determined, and the thermal expansion is measured in the usual way.l We have used this dilatometer to measure the densities of five 2-ketones from -5 to +160° C, with temperature controlled to 0.1" The data were fitted by least squares to power series, and the largest root-meansquare deviation was 1.9 X The densities a t 25" C of four of the ketones agreed with the literature values within 1 X lo-'. G. M. Duff and D. H. Everett4 provide an excellent example of very careful use of this technique, and describe refinements which improve its precision by an order of magnitude.
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Present address: Chemistry Department, De Paul UniverChicago, Illinois 60614. sity,See, e. g., WEISSBERGER, A,, "Physical Methods of Organic Chemistry,', Interscience Publishers (a division of John Wiley & Sons, Inc.), New York, 1945; Vol. I, p. 89. MEYER,E. F., AND WAGNER, R. E., J . Phys. Chem., 70, 3162 (1966). ~ Dnm, G. M., AND EVEEETP, D. H., Tram. Faradav Soe., 52, 753 (1956).
Volume 45, Number 5, May 1968
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