THE BALANCED COLUMN METHOD FOR THE DETERMINATION OF THE DENSITY OF LIQUIDS* Whiie generating carbon dioxide by the calcium carbonate-acid method, and thence conveying the gas into a solution to be saturated, it was noticed that the acid medium rose to a considerable height in the thistle tube. The jet, from which the gas was escaping, was withdrawn from the solution and placed in solutions of diierent densities. In each case a rise of different height occurred in the thistle tube. It thus appeared that the rise in the thistle tube quite likely was a function of the density of the liquid through which the gas was escaping. With this thought in mind the following described apparatus was developed: Figure 1 illustrates, in simple form, the method of balancing one column of liquid against another, as a measure of their respective densities. A small amount of distilled water was introduced into A , and a considerably larger amount into B. The capillary rises, in centimeters, in tubes C and J were recorded. As pressure was applied at G the liquid rose in C until bubbles of air were forced from the mouth of J. At that instant the height of the column of water in C minus the sum of the capillary rises in C and J was exactly equal to the submerged part of J. Another liquid, X, heavier than water, was introduced into B, and the process repeated. The height to which the water rose in C was greater by direct proportion as follows: Rise : Density : : Rise : Density X X Water Water
From this simple device an apparatus as -illustrated in Figure 2 was developed, which is quite as accurate as the Westphal balance or the pycnometer. Since too great a quantity of liquid, whose density was to be determined, was required, and since greater range of rise tended more nearly toward exactness it was decided that tubing of smaller bore and greater length should be used. Tube B measures about 18/r by 45 cm., while the smaller glass tubing is of 2 mm. bore. As with the Westphal balance, 100 cc. of liquid will suffice.
* Presented before the Division of Chemical Education of the American Chemical Society at the Atlanta meeting, April 7-11, 1930. 1910
VOL.7, NO.8
THE BALANCED COLUMN METHOD
1911
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The necessarv , Dressure was obtained by filiing the separatory funnel, I, with tap water, And allowing it to drip into G. When G has been filled to a reasonable height the water may be drained by opening IT, the pressure in G being sufficient to start the siphon. L is then opened in order that the siphoning may continue. B is connected by means of a rubber tube to a drawn-out test tube, E, with which the column in B may be balanced. J is etched at a point near the top of B, in order that, after balancing, the height of all columns of liquid introduced into B may be the same. A, B, and E are immersed in water in a two-liter graduate, F, which acts as a thermostat. Thermometers register both the thermostat and stem temperatures. I t was found that the water in the stem expanded approximately 0.0026 millimeter per centimeter of liquid in the stem for every degree of temperature above that of the liquid in the thermostat, beginning a t 20.0°C. Experimental Part The measured distance between the mouth of J and the etch was 40.45 cm. Distilled water was introduced into A and B. L was then opened, allowing capillarity to exert itself unimpeded. The capillary rises in C and J were, respectively, 1.2 and 0.90 cm.' L was then closed, and pressure applied. As bubbles of air began to escape at the mouth of J,at the rate of about 60 per minute, the column of On account of the fact that it was impossible to obtain two tubes here of the same and uniform bores, capillary rises in C and J were not equal.
JOURNAL OF CHEMICAL EDUCATION
1912
AucusT, 1930
water in B was balanced so that its meniscus was even with the etch on J. The column of water in C was then 42.55 cm. in height,
which discloses the fact that the height to which the column of water had been forced in C was exactly equal t o the submerged part of J. L was opened, and the water in B was transferred to the Westphal balance whose cylinder was submerged in water of the same temperature as that of the thermostat. Its gravity was 0.9998. The temperatures of thermostat and stem were respectively 18.0 and 18.2 degrees C. The correction for stem temperature was, therefore, neglected. The process was repeated with an impure sample of methyl alcohol. The temperature had not altered appreciably. Capillary rises in C and J were 1.2 and 0.30 cm., respectively, while the major rise in C was 34.20 cm. 34.20-(1.2
+ 0.30) = 32.70 cm.
The following proportion was written:
The Westphal balance verified the gravity as 0.8083. With a potassium chlorate solution, heavier than water, the following results were obtained:
X
=
1.0141, as also was given by the Westphal balance. Trricd gravity
Water CHIOH
40.45 32.70
.... 0.8083
0.9998 0.8083
Through a great number of determinations, ranging over a period of two months, results have all been most satisfactory. May I suggest a t this point that the speed with which determinations may be made might be increased if tube C and the meter stick were replaced with a graduated tube; and tube J graduated in millimeters for a short distance on each side of its etch. By means of this apparatus the student of chemistry or physics may see the difference in volumes of liquids of the same weight; may, so t o speak, actually see the differencein their densities. Also, because of the inexpensiveness of the apparatus, which may be easily set up with materials found in every laboratory, it may, due to its accuracy, cope with the Westphal balance or the pycnometer.
