March, 1931
INDUSTRIAL AXD ENGIXEERING CHEMISTRY
reagents. The method used was practically the same as described for mercurous nitrate. A known weight of the substance in finely pulverized state was added to the naphtha and shaken in a shaking machine for 15 minutes. The samples were then allowed to settle for 30 minutes or more before decanting through a dry filter. The naphtha after treatment with chromic acid, ferric nitrate, stannous chloride, zinc chloride, and cupric chloride was water-washed and filtered again through a dry filter. The samples were then analyzed by the lamp method. SuLFInEs--Cupric sulfide remored an appreciable amount of the alkyl sulfides tested, zinc sulfide did not. Both sulfides gave a negative test for free sulfur with the doctor solution and secondary amyl mercaptan. OXIDES-Ferrous, cupric, cobaltic (nickel frc.e), nickel, mercuric, lead, and zinc oxides showed a very slight loss. Ferric oxide showed a loss that was more than experimental. Aluminum oxide gave promising results. This compound has been reported very often in connection with patent literature. Chromic oxide also removed some sulfide, but
323
this may be due to oxidation and thin removal by the mater wash that follolyed. Khile these results are not very promising as to the removal of sulfides, it should be remembered that this work was done a t room temperature. Moreover, some of these reagents are fairly efficient in removing mercaptans ( 2 ) and may be of value with other sulfur compounds that have not been studied. Basic copper carbonate and ferric nitrate did not remove the alkyl sulfides studied to any appreciable extent. CHLORIDES-The naphthas containing sulfides after treatment with zinc chloride showed an appreciable loss and less after treatment with stannous chloride or cupric chloride. References Cited (1) (2) (3) (4) (5) (6) (7)
Borgstrom, I A D E ~ G CHEM, 22, 249 (1930). Borgstrom, Dietz, and Reid, I b i d , 22, 245 (1930) Faragher, Morrell, and Monroe, I b r d , 19, 1281(1927) Mabery, A m Chem J , 13, 233 (1891). Thierry, J Chem S o c , 127, 2757 (1925) Wood, Lowy,and Faragher, IND ENG CHEM, 16, 1116 (1924) Youtz and Perkins, I b i d , 19, 1247 (1927)
Removal of Spray Residues from Apples' A Wax-Solvent Method J. R. Nellerz h C R I C V L T U RAL
EXPBRIMEKT ST.4TIOK,
PULLMAS, W A S H .
Hydrochloric acid is a n effective cleaning agent for 08T of t h e a p p l e s coated fruit sufficiently even apples in most cases, b u t i t sometimes fails with grown in the Westwhen an acid temperature of fruits t h a t have been oil-sprayed or t h a t have become ern States must be the highest degree practicable waxy. I t is shown that a thorough cleaning can be washed to remove spray resifrom the standpoint of cost obtained by first dipping t h e apples in certain wax dues before they are marand injury to fruit is used. solvents, preferably methanol, after which a n unheated k e t e d . T h i s is d o n e as It is with fruit of this type hydrochloric acid wash is able t o dissolve and remove soon after h a r v e s t i n g as that the following results were practically all t h e lead arsenate residue. possible, as the difficulty of obtained using a pre-dip waxcleaning increases after the solvent method. fruit has been stored. Oftentimes it is necessary to harvest the Solvents upon Subsequent Cleaning crop quickly to avoid loss from dropping, and in such cases Effect of Various Wax with Hydrochloric Acid the apples must generally lie in storage for a time before Spray residues of lead arsenate are dissolved rather quickly they can be cleaned. Under these conditions varieties such as the Winesap and Arkansas Black, that tend to exude wax, by washing solutions of dilute hydrochloric acid, provided become so coated that it may be very difficult to clean them. the acid can come into contact with the residues. This is The cleaning of waxy fruit may be even more difficult in case not possible, however, if the residues are covered with an inoil sprays have been put on late in the season over a recently soluble layer of wax and oil. The principle of the pre-dip applied spray of lead arsenate. In regions where frequent solvent method is t o dip the apples in a wax-solvent bath bespraying is necessary it is sometimes impossible to aroid the fore passing them into the hydrochloric acid wash. If a formation of a lead arsenate-oil-wax coating on the fruit. sufficient amount of the wax has been dissolved in this bath, In order more thoroughly to clean m-ax- and oil-covered the acid can then remove the lead arsenate residues. Several liquids known to be wax solvents were tried: acefruit, the acid-washing solution is often heated. This is helpful if the solution is kept warm enough to soften the wax tone, diacetone alcohol, methanol, petroleum ether, chlorocoating sufficiently to allow the acid to reach the lead arse- form, and carbon tetrachloride. Preliminary trials only nate. Experiments by Heald, Seller, and Overley ( 1 ) have were made with chloroform and carbon tetrachloride, as shown that a temperature close to 38" C. must be maintained these liquids discolored the apples. One lot of Winesap apples that was subjected to a pre-dip to effect any material softening of the wax. This is often a difficult and costly procedure, as the constantly incoming fruit wsx-solvent study received a calyx spray and five cover sprays frequently has a temperature as low as 10" to 15" C., and even of lead arsenate a t the rate of 3 pounds per 100 gallons of lower if it has been in cold storage. Another difficulty is water. I n addition the last two cover sprays contained 1 the greatly increased rate of corrosion resulting from the per cent of emulsified oil. There was about a week's delay before this fruit could be cleaned, so that a t the time of cleanaction of the warm acid on the cleaning machinery. It has sometimes been impossible to clean wax- and oil- ing with a commercially operating cleaner the surfaces of the * Received October 22, 1930. Published with the approval of the Di- apples were coated with wax. Because of the distinct oily and waxy appearance of this lot of fruit, a part of it was left rector of the Washington Agricultural Experiment Station as Scientific Paper No. 171, College of Agriculture and Experiment Station, State Coluncleaned for experimental work.8
M
lege of Washington. * Present address, University of Florida, Everglades Experiment Station, Belle Glade, Fla
* This fruit was kindly obtained in the Wenatchee district by F. L. Overley, associate horticulturist of this station.
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INDUSTRIAL -4XD ENGILVEERING CHE-VIISTRY
This fruit carried a residue equivalent to 0.035 grain of per pound (Table I). Although this was not so much arsenic as is often found, the commercial cleaning process reduced the load only to 0.019 grain per pound, which is nearly double the permitted tolerance of 0.01 grain per pound. The machine was of the approved spray type, and for this particular lot of apples a washing solution containing 0.5 per cent by weight of hydrochloric acid a t a temperature of 18" C. was used. I n an attempt to remove more of the residue, the acid st'rength was increased to 0.7 per cent and the temperature of the bath was raised to 24" C., resulting in a slight drop of the residue load to 0.017 grain per pound. When the temperature of the acid solution was increased to 38" C., the washed fruit still carried a residue load of 0.012 grain per pound. I t was then apparent that these apples could not be cleaned satisfactorily even when the acid bath was heated to a temperature too high to be practicable for other reasons. AS203
T a b l e I-Effect of Dipping Waxy Winesap Apples in Wax Solvents u p o n S u b s e q u e n t C l e a n i n g w i t h Hydrochloric Acid EXPT. CLE4NING TREATMEXT .%RSESIC .4S .hS2C).,' Gvain p e r pound 1 Checks, unwashed 0.035 2 Washed in commercial spray machine using 0 5% HCI a t l ? " C. 0.019 3 Washed as in 2 with 0 7 7 , HCl .at 24" C. 0.017 Washed as in 3 a t 38' C. 0.012 o Dippedb in 0 . 1 % HCI for li/n min. a t 20' C. 0.015 6 Dipped in acetone for li/i min. and then as in 5 0,0018 7 Dipped in 50% acetone for 1 1 / 2 min. and then as in 5 0.014 8 Dipped in diacetone alcohol 1 1 / s min. and then asin 5 0 005& 9 Dipped in 75% diacetone alcohol 1 V s min. and then as in 5 0 011 10 Brushed in 75% diacetone alcohol 1 1 / 2 min and then as in 5 0 012 11 Dipped in petroleum ether 1 1 / 2 min. and then a5 In 5 0 008 12 Dipped in methanol 1 1 / 2 min. and then a5 in 5 0 0041 a Average of two or three samples of six apples each b This means dipping with gentle agitation. As shown above and i n previous work ( I ) , this constitutes a treatment giving results similar t o a shorter exposure with a pressure spray wash.
4
I n a laboratory study of the effect of wax solvents upon this lot of fruit it was first dipped with gentle agitation in 0.1 per cent hydrochloric acid for 11/2 minutes a t 20" C. This treatment was used because it was known to be comparable in effect with the commercial method. The fruit under study carried arsenical loads of 0.015 and of 0.019 grain per pound (Table I) after the laboratory and commercial treatments, respectively. Acetone and methanol were among the first wax solvents used because these liquids are miscible with water. I n the first experiments the wax solvent was mixed with the hydrochloric acid wash in the hope that the wax and lead arsenate dissolving processes might progress satisfactorily a t the same time. It was found, however, that satisfactory cleaning could not be obtained when the wax solvent was diluted even slightly. Apples dipped in undiluted acetone lvith gentle agitation for l l / z minutes, followed by a similar treatment in 0.1 per cent of hydrochloric acid a t 20" C., carried only 0.0018 grain of arsenic as As203per pound (Table I). When the pre-dip in acetone was omitted, the acid treatment left an arsenical load of 0,015 grain, this being nearly ten times greater than that obtained when the pre-dip step was included. As shown in Table I, a similar pre-dip treatment with petroleum ether did not clean the apples nearly so thoroughly as the acetone treatment. But since acetone is volatile and inflammable to a dangerous degree, other solvents were tried. Diacetone alcohol and methanol caused the arsenical loads $0 be reduced to 0.0054 and 0.0041 grain, respectively, of arsenic as Asz03per pound. When a 75 per cent solution of diacetone alcohol was used, the cleaning was unsatisfactory even when the fruit was brushed in the alcoholic solution. Particular attention was given t o the thorough cleaning obtained with the methanol as a pre-dip. This methanol was the synthetic product, which is purer and considerably cheaper than that formerly obtained by wood distillation.
Vol. 23, S o . 3
The Winesap apples cleaned by this pre-dip methanol method appeared perfectly normal except that their surfaces were largely devoid of wax and oil. After standing for 2 days a t room temperature they looked and felt almost as waxy as before the methanol treatment. The fruit behaved in a similar manner following the above-described treatment with acetone and diacetone alcohol. Thus it appeared that no appreciable shrinking or drying out of wax-coated apples is to be expected following the use of certain wax solvents. The possible effects upon non-waxy varieties were not investigated, for the reason that the pre-dip wax-solvent step is not needed to obtain a satisfactory cleaning of such fruits. Effect of Temperature on Methanol-Hydrochloric Acid Treatment
In a second experiment Winesap apples were used that had received a calyx and fire cover sprays of lead arsenate a t the rate of 3 pounds per 100 gallons and that carried a residue load of 0.039 grain of arsenic as AssOs per pound (Table 11). The fruit became waxy before it could be cleaned commercially and carried an arsenical load of 0.016 grain following the commercial cleaning treatment with a hydrochloric acid wash spray of 0.5 per cent concentration a t 24" C. When the solution was further warmed to 35" C., the resulting arsenical load was 0.012 grain, or still appreciably above the international tolerance limit. This, then, constituted another lot of fruit that was practically impossible to clean by the hydrochloric acid method. T a b l e 11-Methanol-Hydrochloric Acid T r e a t m e n t C o m p a r e d w i t h Acid Alone a t Different T e m p e r a t u r e s EXPT. AS A S Z O ~ ~ C L E ~ N I S TREATNEST G ARSEUIC Gvain per pound 1 Checks, unwashed 0.039 2 Washed in a commercial spray type machine using 0 . 5 % HCI a t 24' C. 0.016 0.012 3 N'ashed as in 2 at 37' C. Dipped in 0 . 5 % HC1 a t 22' C. for 3 min. 0 .023 4.a Dipped as in 4 a t 45' C. 0.017 6 Dippedin 95% methanol for 1 min. and then as in 4 0.0063 7 Dipped in methanol as in 8 and then in 0 . 7 7,HC1 for 3 min. a t 32' C. 0.0034 8 DiDDed 0.010 .. in 50% methanol for 1 min. and then as in 4 0 Average of two or three samples of six apples each.
After gentle agitation in 0.4 per cent hydrochloric acid for 3 minutes at 22" C., these apples carried an arsenical load of 0.023 grain per pound, When the washing solution was raised to 45" C., the arsenical load was still at the high figure of 0.017 grain and the fruit showed injury from heat. This fruit had been in storage and was even more waxy than a t the time of cleaning attempts by the commercial method. When dipped in methanol for 1 minute preceding a 0.5 per cent acid treatment a t 22" C. for 3 minutes, the arsenical load was 0.0063 grain, or about one-fourth the amount on fruit similarly cleaned without the pre-dip of methanol (Table 11). A similar pre-dip with methanol diluted to one-half strength with water resulted in an arsenical load of 0.010 grain per pound showing that any dilution with water greatly reduces the efficiency of the solvent. When dipped in undiluted methanol preceding a 0.7 per cent acid treatment a t 32" C., a n unusually low residue load of only 0.0034 grain per pound remained on the fruit. Practical Considerations i n Use of Method
Since methanol is an inflammable liquid with a boiling point of 65' C., it should be used with due precaution against. fire hazards. An efficient ventilation system to remove any volatilized vapors would also protect operators from becoming poisoned by the fumes of the liquid. Since the incoming fruit is generally cool to cold (10" to 15" C.), vaporization of the methanol would be slight. Thus it is possible that with further work the method could be employed with the commercially cleaning machines now operating by installing
IlVDCSTRIAL A S D ENGINEERISG CHEMISTRY
March, 1931
a small pre-dip tank to hold the methanol. The fruit in its foreward movement could be carried into and out of the methanol on a simple carrying device, for since apples sink in methanol they would be quiclcly and thoroughly covered. The results indicate that the wax-solvent action would be rapid enough to permit the cleaning machine to be run a t about its customary rate. The apples used in these experiments were unusually difficult to clean. With these the 1minute solvent period mas more than ample, and it is probable that 30 seconds or less would ordinarily be sufficient.
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By using a sloping drain board for the outgoing carrier there should be very little carry-over of the methanol. It could readily be used over again, as it filters easily from the sediment that collects from the dipped apples. After a long period of use it might need to be distilled to separate it from the dissolved wax. This could be done in a still of simple construction as no fractionating column would be necessary. Literature Cited (1) Heald, S e l l e r , and Overleq,
Tvash. Agr.
Expt Sta , Bull. 226 (1928)
Critical Solution Temperatures of Systems of Sulfur Dioxide and Normal Paraffins' W. F. Seyer and Eric Todd UXIVERSITY OF
B R I T I S H C O L U M B I A , T'AXCOUVER,
BRITISHC O L U M B I A
pek-oletini hydrocarions, it seemed desirable t80investigate under what conditions this consideration is true. JIaiiy binary systems of partially miscible liquids have been jtudied with interesting results ever since Abaschew and Alesejen ( 1 ) first opened up this field. Much of this work was actuated by a desire to find a general equation by means of n-hich a curve defining the limits of the coexistence of the two liquid phases could be constructed. The similarity of the critical phenomena in pure liquids to the critical solution temperature (C. S. T.), as well as the similarity in shape of the curves, suggested that this might be possible. This similarity in shape is due largely to the way in mhich the results are plot'ted. By plotting the mol fraction as molal percentage against the temperature a t which one phase disappear., somewhat, different curves are obtained than when the usual method as first recommended by Rothmund I.?) is used. The straight percentage method of plotting tends to mask somewhat the influence of the molecular weights of the components on the C. S, T., which, as d l be shown in this paper, is a n important factor in dealing with partially miscible liquids. A comparison of Figure 3, where t'lie temperatures defining the limits of miscibility are plotted against the numlier of grams of sulfur dioxide in 100 grams of mixt'ure, with Figure 2 . \There mols of sulfur dioxide in 100 mols of mixture are used) shows the difference in the slope of the curves.
The normal hydrocarbons butane, hexane, octane, decane, and dotriacontane were all synthesized in this laboratory. The first four were prepared from the necessary alcohols which had been obtained in as pure a form as possible. These alcohols were converted into the iodides, which \yere in turn treated with sodium. After several distillations their physical properties were measured, and found to agree reasonably well with the constants given in the Critical Tables. S o difficulty was experienced in preparing the dotriacontane by the method of Kraft ( 4 ) from Eastman's c. P. cetyl alcohol. It had quite a sharp melting point a t 70" C. The decane had been prepared several years previously by A. F. Gallaugher from exceptionally pure amyl alcohol obtained from Kahlbaum. Dodecane and tetradecane were purchased from the Eastman Kodak Company and beyond a distillation over sodium to remove water were not further purified. The sulfur dioxide used was the c. P. material put up by Baker in small iron tanks. It was passed through several wash bottles of sulfuric acid and then over phosphorus pentoxide to remove any moisture before being condensed.
Procedure
Determination of Miscible Points
The esperiniental method used was the plethostatic first devised by Alesejew ( 2 ) . By keeping the temperature of the bulbs at the freezing point of the sulfur dioxide before and uliile condensation was taking place, the amount of hydrocarbon lost when the air in the t'ubes was displaced was negligible. A special apparatus was required for filling the tubes with butane and sulfur dioxide. Two 5-liter flasks, d and B in Figure 1, served as reservoirs for the two gases. By means of the tube C they could be connected a t will to a manometer. The tubes to be filled with gases were connected to D. The whole system was evacuated as much as
The miscible points were determined in the usual way. Below 0" C. a bath of acetone was used, from 0" to 80" C., water, and above that, petrolatum. Considerable difficulty was encountered in getting the miscible points when small amounts of hydrocarbon were present, and the temperature difference from the points a t which the two phases disappeared when the temperature of the bath was rising to the point of their reappearance when the temperature of the bath was falling was seldom less than 1" C. I n the neighborhood of the critical temperatures an accuracy of 0.2" C. was attainable. I n no case, however, was the bluish opalescence observed that is so common in the region of the C. S. T. This
I
Received Rovembar 29, 1930.
ofLsulfur d i o x i d e could be introduced, as the volume of the system was known. I n a similar manner the desired amounts of butane could be condensed in each tube. Immediately after the introduction of the butane the tubes were sealed off a t the constrictions. Materials
