Here V denotes the volume of liquid of v i s c ~ s i t ~ , ~ ~ , flowing through a capillaty tube of length, 1, and radius, r, in the time, t, and under the pressure. P.
Finally, unit analysis can be relied upon to tell the form of variance of one quantity with another. It is known that the velocity of a compression wave (sound wave) in a gas varies as the pressure and density of the gas; i. e., Y = f(p,d). Suppose w varies directly as the pressure and inversely with density. We have, if p is measured in dynes
(e)
Here t, is the &tical temperature of the liquid whose surface tension is 7, a t the temperature of the experiment, 1. M is themolecular weight and u is the specific volume.
p- ~ (gm. cm. LC.-=) - dynes ~ m . -d
=
gm. ~ m . - ~
gm. an.-' cm.= set.?
The constant of the Ramsay and Shields' modification of the EBtvBs equation:
Thisshows us that u = d g d , for cm. ~ec.-'adcm.~sec.-~.
(1) Macg AND FRANCE, "Laboratory manual of physi-
2.
Calculate a value of K, the gas consrant, if pressure is m a s ured in pounds per square foot and vulwnc in cubic feet.
3. Are the following equations correct except for their constant factors?
cal chemistry," D. Van Nostrand Co., Inc., New York City, 1934, pp. 1-12. (2) International CritiGal Tables, Vol. I , pp. 1C32.
where w is a weight, a is an area, t is time, and R, T have their usual significance.
p. M.
PROBLEMS
1. What are the units of the following quantities? (a) a in Van der W d s ' equation (h) Equivalent conductivity (c) d(bg 9) if 9 is measured in atmospheres (d) Vismsity. (Use Poiseuille's equation for the flow of liquids through capillary tubes.)
,,=
where v is the drift speed of an ion, Lois the limiting equivalent conductivity of that ion, E is the potential gradient, Fis Faraday's constant. 4.
WP r' -
d in Kcc varies with dT
A H , R, and T.
Determine the form of
the variance by dimensional reasoning.
8V1
.. AN IMPROVED HEATED VACUUM MICRO-DESICCATOR EUGENE W. BLANK Col~ate-Palmolive-PeetCo., Jersey City, New Jersey
*
in operation. The improved desiccator is shown in Figure 1. The desiccator tube has been fitted with a alass ioint I at (A) to simplify the operation of chargin;! and reI l + b moving the de&ant. It is advisable to &an interchangeable joint if possible so that the desiccator may be kept in continuous service if need arises. The thermometer has been placed within the desiccator instead of in a well bored in the aluminum block. - 1 This insures a more accurate temperature control, but the principal advantage secured is that the upper half of the aluminum block may be removed more readily, .m. c and without disturbii~the thermometer, to observe the condition of the ma&ial within the desiccator. T o FIGURE l.-Cnosss~cr~o~ OR AN IMPROVED HEATED VACUUM end it is to have a ring attached to the xt.nma-n-e7m,.aTa* upper half of the aluminum block to faditate handling. In the interim several modifications have been made Other details of the desiccator remain essentiallv the in the original design tending toward greater advantages same. For a fuller description of the apparatus the reader is referred to the original paper already cited. 1 BLANK,J. CHEM.EDUC.,10, 189 (1933).
A VACUUM micro-desiccator heated by means of a micro-burner was recently described in THISJOURNAL.'
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