Reducing Inflammability of Fumigants with Carbon Dioxide R. M. JONES,Iowa State College, Ames, Iowa
T
HE inflammability of certain fumigants employed for controlling insect pests in grain and in other commodities is a serious drawback to their use. When
mixed with air in certain proportions, some of these gases are highly explosive and become dangerous when there is a source of ignition. Jones and Kennedy (4) have effectively solved this problem for ethylene oxide. These investigators report that the addition of 7.15 volumes of carbon dioxide to 1 volume of ethylene oxide gives a mixture which is noninflammable under all conditions a t normal temperatures and pressures. In practice these two gases, having approximately the same molecular weights, may be used a t the rate of 7.5 pounds df carbon dioxide to 1 pound of ethylene oxide. Mackie (6-8) states that the addition of a noninflammable gas, such as carbon dioxide, e l i m i n a t e s t h e danger of carbon disulfide explosions in vacuum fumigation, but gives no data on the dosages or proportions of carbon dioxide mixed with the carbon disulfide. An important argument for the use of carbon dioxide with fumigants was suggested by Hazelhoff (S), who obs e r v e d t h a t carbon dioxide had a marked effect on the r e s p i r a t o r y movements of insects. He states that one may be able to accelerate the penetration of respiratory insecticides into the tracheal system by the application of small amounts of carbon dioxide; in this way the insecticidal FIGURE1. INFLAM- action of a definite concentration of a MABILITY APPARATUS fumigant might be increased, or the same effect minht be obtained bv a lower concentration or by a shorter exposure to the same concentration. The more recent experiments by Cotton and Young (1)and other workers in the United States Department of Agriculture show the possibilities in this field. These investigators report that carbon dioxide materially increased the toxicity of ethylene dichloride, ethylene oxide, carbon disulfide, chloropicrin, and methyl chloroacetate to the confused flour beetle (Tribolium confusum Duv.) and the rice weevil (Sitophilus oryzae Linn.). The amounts of carbon dioxide necessary to reduce the limits of inflammability of carbon disulfide, ethylene oxide, methyl and ethyl formate, propylene oxide, and ethyl acetate are discussed in this paper. The lower and upper limits of inflammability of these gases in air were also determined. The first two fumigants are in common use at the present time, and the others, while not a t present extensively employed, have been shown to possess high toxicity to insects. The experiments of Jones and Kennedy (4) on ethylene oxide have been duplicated in this investigation principally to compare the results obtained under the slightly different conditions of procedure and apparatus. Their curve is superimposed in broken lines upon the one obtained by the writer (Figure 3). The slight variations in the two curves
1
-
may be due to differences in temperature or barometric pressure a t the time the respective tests were conducted.
INFLAXMABILITY TESTS The apparatus for determining the limits of inflammability of the various fumigants was, except for certain modifications, the same as that used by Jones and Kennedy (4) to extinguish ethylene oxide flames. Jones and Perrott (6) emphasize the requisites of Coward and Hartwell (8) when c o n d u c t i n g t e s t s of this 60 nature. These e s s e n t i a l s are quoted as follows: “(I) 8 50 A tube sufficiently large in s diameter so that the cooling $ 40 ? effect of the walls is largely $30 eliminated; (2) a tube long a enough for the observer to 20 be certain that true propagation takes place and con$ IO tinues after the effect due o 4 8 12 16 20 24 to the ignition source has RATIO> BY VOLUME> OF CO, 70 CARBON been removed; (3) the use OISULPHIDE FIGURE 2. INFLAMMABLEof a flame to insure a POSiAREAOF CARBON DISULFIDE- t i v e ignition source; (4) CARBONDIOXIDEMIXTURES t e s t s m a d e under conditions of atmospheric pressure and temperature; and ( 5 ) the propagation of flame taking place under conditions largely free from turbulent effects.” The apparatus (Figure 1) consisted of a large Pyrex glass tube about 6 cm. in diameter and 180 cm. high. The top of the tube was reduced and united to a heavy tube 1 cm. in diameter. This tube led to a Hi-Vac pump, connected by means of appropriate stopcocks and a calcium chloride drying tube. A manometer was attached to the tube lead-
8
7 4 70
< $60
E
2 50 a L
40
$
5
30
20 IO
0 PATJO, BY VOLUME, OF
cor
TO ET~WLENE OXIDE
FIGURE3. INFLAMMABLE AREA OF ETHYLENEOXIDE-CARBON DIOXIDE MIXTURES
ing from the explosion tube. The lower end of the explosion tube was closed during the experiment by means of a ground-glass plate. The modifications mentioned above are of such a nature that they deserve a brief description. When dealing with
3 94
April, 1933
I N D E 3 G I N E E R I N G C H E 31 I S T R Y I N D U S T R 1-4 L .
two gases, one of which is a liquid a t ordinary temperatures, it is somewhat difficult to introduce definite quantities of the liquid into the explosion tube of the standard apparatus. To accomplish this, a 250-cc. flask was connected a t the middle of the explosion tube by means of a ground-glass joint. This flask, after being filled with the liquid to be used in the tests, may be freed of air by either one of two m e t h o d s . (1) by warming the flask slightly over a low flame until the air is d i s p l a c e d b y t h e vapors of the fumigant, or (2) by evacuating the explosion tube until the mercury reaches a height of about 700 mm. and then opening stopcock C until the air is drawn *Arlo, BY VOLUME> OF cot out. The second method was usually TO METHYL fORMATE followed. Another opening into the exFIGURE 4. AREA IN- plosion tube was provided by welding FWMMABLE OF METHYL FOR- a stopcock on t o the tube to which the MATE-CARBONDI- 2.50-cc. flask was attached. Carbon OXIDE ~ I X T U R E s dioxide was let in at this point, instead of a t the top of the tube, as experience showed that complete mixing was in this may more readily obtained. Since the depression of the manometer by the vapors was used as a measure of the quantity of the fumigant in the explosion tube throughout these experiments, it was necessary t o determine how closely the vapors followed the gas laws. The apparatus was calibrated by breaking small ampules containing weighed amounts of the compounds in the tube after the apparatus had been evacua t e d . T h e fumigants v a p o r i z e d almost immediately in the partial ?30 vacuum, resulting in a definite depression of the 5 lo mercury in the manometw. These data when $ plotted as grams against I 5 6 7 RATIO, BY VOLUME, OF cg, TO E ~ H Y L manometer d e p r e s s i o n FORMAT€ assumed a straight line FIGURE5. INFLAMMABLE AREA for each of the fumigants O~ ETHYL FORMATE-CARBON DIOXIDE hfIXTCRES t e s t e d , A comparison of t h e volumes of the tube (Table I), calculated for the various fumigants, confirms the accuracy of these data. The figures given in the table represent averages of a number of observations for each compound. The fall of the mercury required to introduce the desired percentage of the gas is obtained by multiplying this percentage by the prevailing barometric p r e s s u r e . For example, if a mixture containing 3 per cent carbon disulfide and 50 per cent carbon dioxide is desired, and the barometric , /O /Z pressure is 740 mm., then RATlO, BY VOLUMEJ OF COz TO 0.03 X 740 = 22.2 mm., PROPYLENE OXfoE F~~~~~ 6. INFLAMMABLEthe fall for carbon disulfide, AREA OF PROPYLENE OXIDEand 0.50 X 740 = 370 mm., CARBONDIOXIDEMIXTURES fall for carbon dioxide. A n u m b e r of t e s t s showed that it was not necessary to evacuate the apparatus completely, since the percentage of the mixture in the tube is calculated on the basis of the barometric pressure a t the time the test,s are conducted. Evacuation until the mer-
:"
393
cury in the manometer had reached a height of about 600 mm. also resulted in a considerable saving of time. APPARATUS TABLE I. VOLUMEOF COMBUSTION FUMIQANT Carbon disulfide Ethvlene oxide Methyl formate
CALC. VOL. Liters
FUMIQANT
5.29 5.31 5.31
Ethyl formate Propylene oxide Ethyl acetate
CALC.Vor.
Litera 5.29 5.30 5.28
In conducting tests on the limits of inflammability of the various fumigants, the procedure was as follows: (1) The ground-glass plate was placed on the lower end of the explosion tube with a small amount of stopcock grease, and the apparatus was evacuated until the mercury in the manometer had reached a height of about 600 mm. Stopcocks A and B were then closed, and the exact height of the mercury column was recorded. (2) The vapors of the fumigant %erethen slowly let in through stopcock C until the m e r c u r y h a d g'O fallen t h e c a l c u l a t e d $30 n u m b e r of millimeters, 7 after which the d e s i r e d b20 amount of carbon dioxide w a s admitted t h r o u g h $/o stopcock D in a s i m i l a r 4 manner. (3) The rubber hose O RATIO, ey VOLUME, OF co2 TO ETHYL from the carbon dioxide ACETATE E kd: FIGURE7. INFLAMMABLE AREA air was allowed to enter OF ETHYLACETATE-CARBON DIOXIDE MIXTURES through stopcock D until t h e m i x t u r e within the large tube was at atmospheric pressure. This stopcock was then closed. (4) The gases were mixed by means of a light iron strip upon which were glued three circular pieces of thin cardboard. A Iarge eIectromagnet (not shown in Figure 1) was used to pull the mixer u and down the inside of the tube. As observed by Jones and Zennedy, it was found that fifteen trips from the bottom to the top of the tube mixed the gases thoroughly. ( 5 ) In testing the mixture for inflammability the ground-glass plate was removed and the flame from an alcohol lamp passed across the open end. If the flame propagated, or failed to propagate, from the bottom to the top of the tube, the mixture was withdrawn by means of a water suction pump connected to the three-way stopcock, B. In the later tests the percentage of the fumigant was held constant, and the carbon dioxide was either increased or decreased, depending upon the height of the flame, until the flame just failed to burn to the top. The writer observed that a mixture near the limit of inflammability may burn for a foot or so before being extinguished, owing to the heat imparted by the flame from the lamp. The remaining points for the curves were established in a like manner. Ir
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RESULTSOF TESTS The data obtained during this investigation are presented in Tables 2 to 7 and Figures 2 to 7 . The solid dots on the graphs represent mixtures which just failed to burn to the top of the explosion tube, whereas the circles denote mixtures which are inflammable and unsafe to use. The diagonal lines bring out more clearly the areas of inflammability. TABLE 11.
MIXTURES OF CARBON AND
DISULFIDE, CARBON DIOXIDE,
AIR
(Barometric uressure. 739-747 mm.: temu.. 25-29O C.I INFLAMMABLE MIXTURES NONINFLAMMABLE MIXTURES Ratio (by vol ) Ratio (by vol.) Mixture in air of COz to CS? Mixture in air of Con t o C&
% 1.50 5.00 16.00 28.00 35.00 39.75 48.00 53.50 67.00 58.00 58.00 57.00 52.00 44.00
% 0.0 2.3 7.9 14.0 19.0 21.7 22.0 20.4 18.0 13.5 10.6
6.1 2.4 0.0
1.25 5.on 15.00 25.00 35.00 40.75 47.00 54.50 58.00 59.00 59.00 58.00 52.50 45.00
0.0 3.0 9.0 15.7 20.5 22.3 22.5 20.8 18.3 13.8 10.8 8.3 2.5 0.0
70
%
:i . 50 10.50 18.25 30.00 35.00 40.00 45.75 44.00 41.50
0.0 1 6
3 ~ 3 5.7 0.5 7 0 7.0
6 .a
3.00 11.50
19.00
31.011
as. 00 41.00 46.73 45.00
39 .00 38.00
37.00
5.4 4.0 3.7 2.7 2.1
38.00 45.00 53.00
1.7 1.2 I1 8
40.00
7i.60
0.0
39.00 3R.00 37.00
42.50
moo
38.00 39.00 55.00 68.00
no. oo
0.0 1.9 3.5 6.0 6.8 7.2 7.1 6.5 5.5 4.7
a.9
2.8 2.2
i s
I :3 0 9 0.4
0.0
. Carbon diaulhdr I.:thylene oride Methyl formute Ethyl forillnLr Pmpyloiie oxide Nthyl rcelnte
%
%
1.25 3.00 6.00
45.0 80.0
a.50
14.0 22.0 9.0
e.00 ".00
20.0
.
Pound* 22.20tui
7.15t"I 2.30to 1 6.05 to i 11.00 to 1 6 . 2 5 Lo 1
12.9to1 7.2tll1 1.7 t o 1 3.5 to I 8.3 t o I 3.1 t o I
ACKXO WLEDGMENT Tlie.sc stiuliea were conducted in tire 1Jioclieinicai IAboratory, Ilepartnrent of Chemistry, Iowa State College. The writer wishes to express his tlianki to R. M. Hixon arid L. D. Goodhue, Dep:%rtmentof Clrcmistry, xiid to C. H. Richardson, Uepartinerit of Zoology and Entomology, for suggestions and criticisms during the investigation. Especial appreciation is due The Liquid Carlmiic Corporation, Chicago, Ill., and the Crop Protectiori Institute for a felloudiip grant to determine the efficiency of fumigant-carbon dioxide mixtures in controlling insect pests of grain.
.. 3.00 19.00 20.25 29.50 g4.w dl.00 28.00 24.00 22.w 17.00
1a.w
T ~ n r . xV I .
11.0
3.8 6.2 5.6 5.8 4.2 3.0
2.0 1.4
0.4
0.0
a.50 20. 00 27 , 2 3 :io. 50
86.00 32 .I10 29.00 25.w a3.w 18.00
14.00
0.0 4.0 5.4
5.8 6.0 4.3
3.1 2.1 1.6 0.5 0.0
% 0.0
2.00
3.6 9.9 10.7
29.00 26.00 23.00
3.8 2.7
32.511 31.00 36.00 88.50 37.00 33.50 8J.00 30.00
21.00 21.M
c.1
/"
11.50 30.00 35.00 37.50 86.00 34.50
3 2 . 00
(I) Cottorr and Young, ?'roc. Entornot. Suc. WasIw,wIom. 31. !Ji (Il329,. C2) Coward and Hartwell, J . (,"hem. Soc., 129, I522 (1926). (3) Hazelhoff. I. Econ. Ennlornol.. 21, 790 (19'28). (4) Jones and Kennedy, IND.ENG.C a e x . , 22, 146 (1030). (5) Jones nnd Perrott, I M . . 19, 985 (IS27). ( 6 ) Machic, Mo. Bull. Calij. Depl. ilgiic.. 13, 160 (1%24).
(7) Ibkt., 15, 121 (1926). (8) Z b d . , 17. 672 (lQ28).
Mix.ru~ieaOF PL~OPYLENE OXIDE,Cn~irro~ DIOXIDE, ItX
