*
ANALYTICAL EDITION
38
of his three sets of readings there should be satisfactory overlapping checks. With experience and everything going smoothly all three sets of readings are not necessary for assurance of good checks. Satisfactory results having been obtained for the temperat u r e u n d e r test, the l i q u i d P i n N i s removed, after removing the flame, the next desired bathliquid poured in through n, and temperature and pressure tests made as before. As the higher boiling liquid, P, i i heated up, a small amount of air is let in through L and J to adjust the pressure within A so that too vigorous boiling of sample G will not occur. The presence of small amounts of air a t J has no influence on the vap o r pressure-temperature relationships inside A so long as the thermometer bulbs are Figure &Relative Accuracy of Modifled A paratus when Used t o Detc mine surrounded by only the (8urve 1) Vapor Pressure of Water and liquid and vapor phases (Curve 2) Vapor Pressure of a Saturated Sodium Chloride Solution of the material under test. Temperatures higher or lower are adjusted by proper temperature baths in N .
Vol. 1, No. 1 Pressure of Water a t O 0 C. Using Modified Method
Table I-Vapor
TEMPERATURE OBSERVED
LANDOLTBORNSTEIN
INTERN. BUREAU WEIGHTSAND MEASURES
c.
Mm. Hg
M m . Hg
M m . Hg
13.0 16.5 19.2 20.2 21.4 22.2 23.9 24.5 25.6 26.0 26.7 55.0 55.6 90.0 91.15 92.2 92.6
11.1 13.9 16.3 17.6 18.9 19.9 22.0 22.9 24.3 25.1 26.0 117.0 120.6 523,5 547.6 569.5 578.0
11.23 14.08 16.69 17.75 19.10 20.07 22.24 23.06 24.62 25.21 26.27 118.04 121.47 525.76 549.10 571.26 579.87
11.14 13.95 16.52 17.58 18.92 19.87 22.02 22.83 24.37 24.96 26.01 117.52 120.95 525.47 548.87 570.98 579.61
O
Table 11-Vapor Pressure Data on Saturated Sodium Chloride Solutions, as Obtained by Improved Apparatus (Pressure corrected for mercury at O o C.) TEMPERATBMPERATEMPERATURE
PRESSURE
OC.
M m . Hg
15.0 15.1 15.3 16.0 16.1 53.1 53.2 53.4 53.5 53.6
8.5 8.6 8.8 9.0 9.1 80.1 80.9 81.3 81.9 81.7
TURE
PRESSURE
C.
M m . Hg
53.7 53.8 53.9 55.4 55.5 55.6 84.8 85.0 85.1 85.1
82.4 82.8 83.3 89.9 90.1 90.4 319.0 322.1 323.1 323.5
TURE a
C.
PRESSURE
M m . Hg
85.3 85.5 85.5 85.6 85.7 85.7 85.8 86.9 86.0 86.1
Curve 2, Figure 5, was plotted from data from LandoltBornstein tables for saturated sodium chloride solutions. Against this curve are plotted, by circles, data obtained on saturated sodium chloride solutions using the apparatus described. These data show the relative accuracy attainable by the method described. Such accuracy can beattained by the average laboratory worker with ease and without sacrifice of speed. It is easily possible to get such data over a temperature range of 10" to 220" C. in a total time of from 2 to 4 hours, ifpressure readings to 0.1 mm. are sufficiently accurate for the desired purpose. Application of this apparatus can be extended. It can be used for determining the vapor pressure of solids in the same manner as described by Ramsay and Young for their original apparatus. Volatile corrosive materials might be tested by modifying the closure, B, of A in Figure 3.
Standardization
In order to test the accuracy and applicability of the method for the desired purpose, vapor pressure-temperature data were obtained using redistilled water. The data are given in Table I, and the closeness with which they fall on curve 1, Figure 5, plotted from Landolt-BiSrnstein data, shows the relative accuracy of the method, Greater accuracy could be attained easily by use of more refined pressure readings than used here, where 0.1 mm. was satisfactory. The method should also be as applicable for pressures lower than 0.1 mm. Another operator in this laboratory has shown the method to be highly satisfactory for determining vapor pressure data on saturated salt solutions.
Acknowledgment
The author acknowledges his indebtedness to J. M. Peterson for the data on saturated sodium chloride presented in Table 11, and to E. A. Lantz for part of that in Table I.
Simple Apparatus for Measuring Vapor Pressure of Volatile Liquids' Alfred W. Francis ARTHURD. LITTLE,INC.,
V
ARIOUS forms of apparatus have been used for determining the vapor pressure of gasoline. The serious errors inherent in many of these have been pointed out by Davis.* For this purpose an apparatus has been devised which measures the vapor pressure in a Torecelli vacimm,8 but the method of use is simplified greatly, The apparatus 1 Received
November 9. 1928.
* Dasis, IND. ENO.CHEM.,17, 1136 (1925). * Engler-Hofer,"Das Erdol," Vol. IV, p. 33 (1916).
CAXBRIDGE,
MASS.
consists merely of a small longatem dropping funnel supported preferably by a split ring and connected by a rubber pressure tube with a gas-analysis leveling bottle (bottom outlet) containing mercury. In practice, the funnel is first lowered until mercury flows into it, the stopcock is shut off, and the funnel is raised until mercury fells away from the stopcock. The height of the mercnry is read on a meter rod. This is repeated two or three times to obtain a constant reading, which is usually 3 or
January 15, 1929
INDUSTRIAL AND ENGINEERING CHEMISTRY
A
4 cm. below the barometer reading, b e c a u s e , of dissolved air, vapors, etc. T h e constant height is taken as the zero reading. A few cubic centimeters of the volatile liquid are then poured into the funnel, which is stopped loosely to avoid excessive evaporation. The funnel is lowered again with the I I stopcockopen, and then shut off with volatile liquid on both sides of the stopcock. Again the funnel is raised and the new height of mercury (a) read as before. The difference
I I I ii
39
in height gives the vapor pressure of the liquid a t the surrounding temperature. The correction for height of the liquid column (a-b) is within experimental error. For other temperatures a jacket of warm water or steam, etc., around the whole stem of the funnel must be provided. With impure liquids, such as gasoline, the observed vapor pressure as determined by any method varies greatly according to the volume of the vapor space, far more than the abovementioned error due to air dissolved in the mercury, so that it is useless to eliminate the latter completely. For comparison of gasolines the ratio of vapor to liquid volumes must be set arbitrarily, and this adjustment is particularly convenient with this apparatus. The ratio might be 1:9, corresponding to a tank 90 per cent full. For fairly pure liquids, such as commercial acetone, ether, etc., a much higher ratio, five, to ten times the liquid volume, would be preferable. Results agreeing well with literature values have been obtained for ether, acetone, benzene, carbon tetrachloride, chloroform, and pentane. The time for a test is 5 to 10 minutes; for check determinations, less than 1 minute.
Rapid Determination of Specific Gravity of Semi-Solid Bituminous Substances' S. E. Berkenblit BOARDOF TRANSPORTATION OF THE CITY OB NEW YORK,49 LAFAYETTE ST., NEWYORE,N. Y.
HE specific gravity of semi-solid bituminous substances both ends and cut longitudinally in two equal parts, which is usually determined by means of a wide-mouth are held together with a rubber band. The mold can hold pycnometer or by the Sommer hydrometer. I n either about 40 grams of asphalt or pitch. It is placed on an case the solidified material has t o be removed after each de- amalgamated brass plate and the molten sample poured into termination, so that the cup holding the sample may be it. cleaned and made ready for the nest test. GLASSCYLINDER-This cylinder is 8'/2 inches (21.6 cm.) The cleaning of the apparatus usually consumes more time high and 13/4 inches (4.4 cm.) in diameter, open a t the top. than the actual determination and causes considerable slop- At the bottom a three-hole rubber stopper is inserted, from piness. Moreover, the delicate glass pycnometers very often which one connection is made to a 500-cc. separatory funnel, , break during cIeaning, and with the Sommer hydrometer serving as a leveling bottle. Another connection leads to a difficulties are frequently encountered in the removal of 50-cc. buret, the lower end of which has been cut off below the cover and flange from the metal cylinder, as a result of the zero mark. Both the buret and the leveling bottle are held a t the desired height by which the cylinder gets scratched or indented. The writer has developed a sho;t method eliminating the means of an iron support. Into cleaning of the pycnometer and requiring only one weighing. t h e t h i r d hole of the rubber E This method has been used for over three years in this labora- stopper is inserted a glass tube, tory for determining the specific gravities of asphalts employed '/4 inch (6 mm.) inside diameter, for waterproofing purposes in the subways and ranging in leading to the outside of the melting point from 125" to 175" F. (51.7" to 79.4" C.) (ball c y l i n d e r , parallel to its side. M and ring), and has been found to give very satisfactory re- This glass tube has a mark etched sults. Duplicate analyses made on the same material have on it, 5 inches (12.7 cm.) from been found to check within 0.002. The method can be used the lower end. The glass cylinto advantage in connection with all kinds of solid and semi- der with the side-tube attachment may be clamped in another solid materials. A detailed description of the method and the apparatus iron support. This apparatus is not expenrequired is given below. I n the method described the specific gravity is obtained at 77" F. (25" C.), which is the tempera- sive and can be constructed in ture specified in the A. s.T. M. Standard Method of Test for any laboratory. Specific Gravity of Asphalts and Tar Pitches, Serial DesignaPreparation of Sample tion D71-27. The sample of the bituminous Description of Apparatus substance is melted in a tin can BRASSMom-This consists of a brass tube, 13/4 inches at the lowest possible teppera(4.4 cm.) high and ls/16 inches (3.3 cm.) in diameter, open at ture and poured into the brass , , ~ ~ ~ ~ mold to fill it slightly more than Bituminous Substances 1 Received October 30, 1928.
T
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