September, 1930
I N D U S T R I A L AND ENGINEERING CHEMISTRY
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Vapor Pressures of Fumigants IV-l,1,2,2-Tetra-, Penta-, and Hexachloroethanes's' 0. A. Nelson INSECTICIDE DIVISION,BUREAUOF
CHEMISTRY AND SOILS, WASHINGTON, D.
NUMBER of alkyl chlorides have been tested by different investigators for their effectiveness as fumigants (1, 6). Tetra- and pentachloroethanes have shown some promise as fumigants against certain pests, while hexachloroethane has been suggested as a possible substitute for naphthalene and paradichlorobenzent?, against moths (4, 6). In previous publications data have been given on the vapor pressures of chloroacetates, formates, and nicotine because of their promise, or established effectiveness, as fumigants against a variety of harmful pests ( 2 ) . I n this paper results are given on the vapor pressures of tetra- and pentachloroethanes froin room temperature to above their boiling points, and of hexachloroethane from room temperature to about 60" C.
A
Methods of Determining Vapor Pressure
The method used in the determination of the vapor pressures of tetra- and pentachloroethanes was the same as that used for the chloroacetates, formates, and nicotinenamely, the static method as developed by Smith and Menzies, and used by the author in determining the vapor pressures and boiling points of a number of different compounds (9). The vapor pressure of hexachloroethane was determined by the air-saturation method, and since the apparatus was designed for relatively low pressures the data for this compound do not extend above 60" C. The reason for using this method instead of the static was that this compound melts at about 185" C., at which point it also sublimes very rapidly. I n the static method, especially when the compound under investigation is used as the confining liquid in the isoteniscope, the work must obviously be carried out at a temperature above the melting point of the compound in question, and compounds that have appreciable sublimation pressures sublime into the colder portions of the isoteniscope, thereby clogging it, before equilibrium between the outside and the inside can be established. Furthermore, fumigation operations are never carried out at temperatures much above that of the surroundings, so for this reason also it was considered not necessary to devise special apparatus which would have been necessary for vapor-pressure determinations a t higher temperatures. Methods of Purification
The tetra- and pentachloroethanes were purified by careful fractional distillation. Fractions whose boiling points were constant to about 0.1' C. were redistilled under reduced pressure, in order to ascertain that the distillate was a pure compound and not a constant-boiling mixture. The criterion for purity was that the compound must boil a t the same temperature before and after being subjected to distillation under 1 Received April 3, 1930. Presented as a part of the Insecticide Symposium before the Division of Agricultural and Food Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, G n . , April 7 to
11, 1930. 2 The previous article of this series, appearing in the April, 1929,issue of INDUSTRIAL A N D ENGINEERING CHEMISTRY, was numbered IV when it should have been 111. Attention was called to this error in the June, 1929, number.
C.
reduced pressure. These compounds passed this test before vapor-pressure determinations were made on them. Hexachloroethane was purified by fractional crystallization and careful sublimation. Vapor Pressures of Tetra- and Pentachloroethanes
I n Tables I and I1 the observed vapor pressures a t different observed temperatures are given. The temperature was measured by Anschutz thermometers that had recently been standardized at the Bureau of Standards, and could be read to within less than 0.1" C. by the aid of a hand lens. The pressures were read off directly from the manometer, and with the aid of a magnifying glass could be read to about 0.2 mm. The results thus observed were then plotted on coordinate paper and the pressures read a t 5.0-degree intervals from the smoothed curves. A comparison of the calculated values with these observed values is also given in the tables. Table I-Vapor OBSD.
TEMP.
c.
31.1 34.6 89.3 44.3 50.4 57.8 64.6 72.3 79.0 88.0 89.9 94 9 99.9 105,O 109.1 114.9 119.9 120.1 122.5 124.5 130.4 135.2 141.5 145.1 146.5 146.7
Pressures of 1,1,2,2-Tetrachloroethane
V.4POR
PRESSURE OBSD.
Mm. 7 5 8 0
ii.5 16.5 23.4 31.9 44.2 62.2 81.6 104.0 125.9 153.3 184.6 223.9 260.8 313.0 357.8 364.3 407.4 411.5 497.5 573.7 691.1 767.2 800.1 802.1
TEMP. O
c.
Mm.
20
4.7
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145
8.2 10.7 13.9 17.9 22.8 28.9 36.3 45.3 56.1 69.2 84.7 102.6 125.2 150.9 180.9 216.0 256.6 303.5 387.5 419.3 490.0 570.3 661.3 764.1
2.5 -.
a Calculated by means of equation: log
PRESSURE OBSD.F R O M CURVE Mm.
VAPOR PRESSURE CALCD.~
...
... 7.0 9.0 12.4 15.5 22.0 28.0 36.0 45.2 56.0 69.2 85.0 103.0 125.0 151,O 183.0 219.0 260.5 306.0 360.0 419.5 490.0 571.0 662.0 764.0
6 2
P
-
8.06938
-2 167.83 T (ab%)
Vapor Pressures of Hexachloroethane
I n determining vapor pressures by the air-saturation method it is essential that the air (or gas) be completely saturated with the substance under investigation, and also that the temperature be maintained constant throughout the individual runs. The apparatus devised for this work consisted of a constant-temperature bath, with which the temperature could be maintained within *0.1" C. during the periods required for each run, and a train to ensure complete air saturation. The latter consisted of the equivalent of two U-tubes sealed together and filled with pieces of glass tubing to provide increased surface. When hexachloroethane was sublimed directly into these tubes, the entire surfaces of the inner side of the U-tubes and those of the glass tubing within became covered with minute crystals of the compound. The air current had to pass over finely divided hexachloroethane for a distance of approximately 25.0 cm. before entering the absorption chamber. Two liters of air were passed
INDUSTRIAL A N D ENGIYEERING CHEMISTRY
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through for each run, and it was determined that if the rate of flow was adjusted to about 1 liter in 8 or 10 minutes complete saturation was a,ssured. This was ascertained by passing air through at different rates. Table 11-Vapor OSSD.
TEMP.
c.
Pressures of Pentachloroethane
VAPOR PRESSURE OBSD.
Mm.
TEMP.
c.
VAPOR PRESSURE
CALCD.~ Mm.
L'APOR PRESSURE OBSD. FROM CCRVE
M m, 2.5 3.5 4.5 6.0
a
Calculated by means of equation:
log P = 7.80304
8.0 10.0 13.0 16.0 20.0 25.6 32.0 39.0 48.0 59.0 72.0 87.0 105.0 125.0 148.5 178.0 209 5 245.3 288.2 334.0 386.5 447.0 512.5 586,O 670.0 764.0 870.0 2129.6
F'ol. 22, s o . 9
similar to that used for the compound, which was submerged in the same low-temperature bath, before going into the air saturation train. The vapor pressure was calculated by means of the following formula based on Dalton's laws of partial pressures: w VcTP760 Vapor pressure (mm.) = 760 wVsT 273Vp w = weight. in grams Vs = spehfic vohme = 22.41/M.W. = 0.09489 liter per gram P = barometric pressure, in mm. V = volume of air, in liters T = absolute temperature of air in aspirator = pressure of air in aspirator, in mm.
+
Table I11 shows the results obtained on hexachloroethane. Table 111-Vapor Pressures of Hexachloroethane VAPORPRESSURE TEMPERATURE VAPORPRESSURE TEMPERATURE c. Mm. c. Mm. 15 0.15a 40 1.OOb 20 0.22a 45 1.49b 25 0.32a 50 2.12b 31 0.55b 55 2.93b 35 0.70b 60 4.105 a Pressures obtained from curve. b Pressures obtained from experiment.
Importance i n Fumigation Work
- T(abs.) -
The saturated air was then passed into a U-tube condenser partly submerged in carbon dioxide snow-ether slush having a temperature of about -78" C. At this temperature the hexachloroethane has no appreciable vapor pressure, and is thus completely condensed. The intake end of the condenser system extended inside the air saturation train to a point well below the surface of the constant-temperature bath. It is obvious that the air used for these experiments must be thoroughly dry, otherwise, not only hexachloroethane, but also water will condense in the low-temperature condenser ( 3 ) . For this reason the air was passed through a calcium chloride tower, then through a condenser tube,
I n fumigating work it is essential to know how much of a certain fumigant can vaporize into a fumigating chamber of a given size. I n the previous publications on vapor pressures of fumigants formulas were given whereby these calculations could be made. The same formulas may of course be applied to the compounds discussed in this paper. It must be remembered, however, that the results obtained by the use of these formulas do not take into account losses due to faulty fumigating chambers or adsorption of the fumigant on the surfaces of the materials within the chamber. Literature Cited (1) Neifert, Cook, Roark, Tonkin, Back, and Cotton, U. S. Dept. Agr., Bull. 1313 (1925). (2) Xelson, IND. ENG.CHEM.,20, 1380, 1382 (1928); 21, 321 (1929). (3) Nelson and Hulett, I b i d . , 12, 40 (1920). (4) Parker and Long, Bull. Bur. Bio-lech., 4, 102 (1921). (5) Roark and Cotton, J. Econ. Enfomol., 20, 636 (1927); 21, 135 (1928). (6) Tattersfield and Roberts, J. Agr. Sci., 10, 199 (1920).
Some Less Familiar Applications of Soluble Silicates1 James G. Vail PHILADELPHIA QUAWI"C COMPANY,
121 SOUTH THIRDST., PHILADELPHIA,P A .
ILICATE solutions of the same NazO content may vary widely in pH. A tenth-molar solution, for instance, may show anything between 10.8 and 12.4 (2, 9) according to the ratio between NazO and SiOz assuming the limits to be NasO :SiOz (sodium metasilicate) on the alkaline side and NazO:4Si02 on the side of highest silica content. As a matter of fact these limits, which have been set for industrial convenience, are not impassable boundaries, for sodium orthosilicate, 2Naz0:SiOn, is known, and in relatively dilute solution diminishing amounts of alkali may be present until one containing only colloidal silica is reached. It is possible to make a silica solution a t any desired pH and to traverse the range from 9 to 14 without being bound by narrow limits of concentration. A twice-normal solution of sodium metasilicate has a pH of about 13.4. The degree of hydrolysis
S
* Received June 14, 1980.
varies, but it is always low in comparison with the hydroxylion concentration in corresponding sodium hydroxide solutions. For ratios more siliceous than 1:1, and concentrations above molar, i t is less than 6 per cent. The strong buffer action of the silica also makes it possible to meet a variety of requirements. These and other phases of the adaptability of silicate solutions have led to some strange proposals for their use. The excuse for gathering here some of the less familiar applications is that they may contain suggestions for solving other problems. Treatment of Ripe Olives
The process of making ripe olives fit to eat includes treating them in a solution of caustic soda. Relative to the green olives on the market the fruit is ripe, but the degree of ripeness permissible is limited by the softness of the cured olives.
