CHEMICAL-ACHIEVEMENTS OF THE U. S. DEPARTMENT OF AGRICULTURE The Use of Ethylene in Hastening the Coloration of Citrns Frnit Oranges and lemons which are ripe enough for the market are not always yellow all over. Citrns fruits may be commercially mature and still have a green surface color. Therefore the yellow color, if immediately desired, must be brought out by some special treatment. Storing the fruit in boxes under suitable conditions produces the yellow color in a month or two. Many years ago it was found that this period could he cut down to a week or so by placing a kerosene stove in the room containing the fruit and properly adjusting the flame. Sievers and True showed that the increased rate of change was caused by the gaseous combustion products, the identity of the gas mainly responsible being at that time unknown. The kerosene-stove method was unsatisfactory in so many respects that the Bureau of Chemistry undertook a series of experiments to determine the nature of the effective gaseous constituent. The results indicated that the coloration was caused by traces of ethylene in the air of the storage room. The availability of pure ethylene in commercial quantities as a compressed gas in cylinders permitted a practical application of the results of this investigation. A mere trace of ethylene is sufficient to turn fruits from green to yellow. As a result of the Bureau's investigation, the ethylene method is rapidly replacing the kerosene-stove method, over which it has the following advantages: Greater convenience; reduction of fire risk; no need for constant supervision; no exposure of workmen to the foul-smelling, tear-compelling atmosphere generated by stoves; no sooting or absorption of odors by the fruit; no wilting and shrinking of the fruit during the warm season; rigid standardization of temperatures, humidities, and gas concentrations, which insure uniform results.-U. S. Bureau of Chemistry, Washington, D. C. The Catalytic Air Oxidation of Vapor Phase Naphthalene to Phthalic Anhydride The shortage af phthalic anhydride and its derivatives during the World War led Gihbs and Conover, then of the Color Laboratory staff, into an
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investigation of the then prevailing method of oxidizing naphthalene by the use of sulfuric acid in the presence of a mercury salt. The results obtained were very disappointing and led these investigators to take up the catalytic air oxidation process, using various oxides as catalysts, which Gibbs had previously used in oxidizing toluene in the vapor phase to benzaldehyde and benzoic acid. The results obtained from mixing naphthalene in the vapor state with air and passing this mixture over either vanadium oxide or molybdenum oxide heated to approximately 500°C. soon indicated the presence of an appreciable amount of phthalic anhydride in the reaction products. Out of a large number of oxides later tested out as catalysts the two mentioned above proved to be superior to the others tried, the advantage resting with vanadium pentoxide. The demand for this highly important intermediate, which has already been used in the preparation of about two hundred compounds, has been continually on the increase, last year's production in the United States being approximately four million pounds. Owing partially to war-time conditions and partially to difficulty of manufacture under the old process, phthalic anhydride sold in 1916 in small lots for as much as fourteen dollars per pound, while today it sells for about twenty cents per pound.-U. S. Bureau of Chemistry, Washington, D. C. Invertase The principal advantages of inversion of sucrose in commercial practice are as follows: (1) Increase in solubility of total sugars, thus making i t possible to prepare a non-c~stallizingsirup of increased density; (2) retarded drying of such products as fondant confections and icing due to presence of lewlose; (3) formation of small& crystals, thereby improving the consistency of fondant confections, icings, etc.; (4) modification of flavor. The enzyme invertase is more suitable than acids for the inversion of products such as sugar cane, maple, and sorghum sirups, "la mite" and sirups prepared from raw or other low grade sugars which exert considerable buffer action toward acids and which require such amounts of acids as to unfavorably affect flavor-also for manufacturing golden simp by direct inversion of an intermediate refinery sirup. The latter is a more direct process than that customarily used which consists in inverting granulated sugar sirup with acid and mixing same with refiners' sirup. The use of invertase in maple cream (a fondant prepared from maple sugar or sirup) makes possible the production of a smoother fondant (smaller sucrose crystals) of more homogeneous consistency.-. U. S. Bureau of Chemistry, Washiigton, D. C.
Fumigation of Grain against Weevils Weevils destroy many million dollars worth of wheat and other grains annually. Carbon disulfide is extensively used as a fumigant against these insects but on account of its ready inilammabiiity and the explosibility of a mixture of its vapor with air, f i e insurance companies refuse to carry the fire risk on elevators or buildings during the time carbon disulfide is being used to treat the grain contained in them. Owing to this fact, and also because no effective substitute for carbon disulfide for fumigating purposes was known, the General Managers' Association of Chicago, representing the leading railway systems of the United States, requested the Uaited States Department of Agriculture to undertake an investigation having as its object the development of a substance which could be used for destroying weevils in grain with safety from fire hazard. In compliance with this request, the Bureau of Chemistty, in cooperation with the Bureau of Entomology, tested the action of more than 100 organic compounds on the rice weevil, the granary weevil, the flour weevil and the Indian meal moth under conditions permitting a control of the factors of concentration, time, and humidity, and with observations of the temperature. While about 30 compounds were found to be more toxic than carbon disulfide to the rice weevil, under laboratory conditions, fumigation tests against this weevil when present in wheat in boxes, barrels, and railway box cars eliminated all economical fumigants except ethyl acetate. In order to reduce the fie hazard which would result from the use of ethyl acetate alone, it is mixed with carbon tetrachloride in the ratio of 35 to 40 volumes of ethyl acetate to 65 to 60 of carbon tetrachloride. This mixture has been carefully tested under practical fumigating conditions in box cars and grain elevators, and when used a t the rate of 40 to 45 pounds per 1000 cubic feet of enclosed space is effective in killing all weevils. It is non-inflammable and the vapor of the fumigant in mixture with air is not explosive a t temperatures up to 120°F. This fumigant has a pleasant odor and is not injurious to those handling it. I t does not lower the germinating quality of seeds and the quality of flour and bread from wheat which has been treated with this fumigant is not injured. The fumigant, ready mixed, is now obtainable a t a price which figures to less than 1 cent per bushel of fumigated wheat when applied in an elevator. The method of applying the fumigant is identical with that used with carbon disulfide. Great benefit will result to those producing and handling wheat and other cereals from this development of a fumigant which can be used without voiding the fire insurance on the buildings used to contain the grain. The results to this investigation in detail are given in U. S. D. A. Bulletin No. 1313, January 26, 1925.-U. S. Bureau of Chemistry, Washington, D. C.
Products from Plants The products exhibited by the Phytochemical Laboratory were selected with a view to representing some of its more notable achievements. The purpose of the respective investigations and the results obtained are very briefly noted. Caffeine.-During the World War the material which had hitherto been available for the production of caffeine became very much diminished in quantity and new sources for this important organic compound were therefore sought. It had previously been observed that caffeine is contained in one of our native species of Holly (Ilex vomituria) and a more extended investigation of the subject has shown that it would be possible to utilize the leaves of this plant for its production. Another soure of caffeine that had not previously been considered is the pulp of the coffee berry. Although this material is accumulated on the coffee plantations in very large quantities, it has always been regarded as a waste product and suitable only for fertilizing purposes. In connection with this investigation a method was devised for the accurate quantitative determination of caffeine in holly leaves as well as in tea, coffee, and other plant products containing it. The Odorous Constituents of Fruits.-It is only within recent years that anything has been known regarding the nature of the substances which impart to certain fruits their characteristic odors. An investigation of the apple has shown that its fragrant odor, and to a certain extent the flavor, is due to a complex mixture of substances, consisting chiefly of amyl esters and acetaldehyde together with a small proportion of geraniol or its esters. As a result of this investigation it was found possible to produce a synthetic apple oil which is well adapted for imparting to beverages, ice cream, etc., the characteristic apple flavor. The odorous constituents of peaches have likewise been examined, and these have been found to consist chiefly of esters of linalool, together with a considerable proportion of acetaldehyde. An examination of a large number of authentic grape juices has established the fact that the odor of certain varieties of this fruit is due in part to the presence of methyl anthranilate and a method was devised for its detection. The Odorous Constituents of the Cotton Plant.-The investigation of this subject was undertaken in order to ascertain the nature of the substance which is presumed to attract the boll weevil. In the course of this work, which extended over a period of nearly two years, a large number of definite chemical compounds were isolated from a distillate of the plant. Some of these substances had a very pleasant odor, but it was found that the distillate also contained appreciable amounts of ammonia and trimethylamine. It was furthermore ascertained that these two basic substances are constant exhalations of the plant. The results of this investiga-
tion Will, therefore, form a basis for more extended entomological experiments in the control of the boll weevil.-Phytochemical Laboratory, U. S. Bureau of Chemistry, Washington, D. C .
Furfural Research by chemists of the Bureau of Chemistry, U. S. Department of Agriculture, on the production of furfural has resulted in the development of a cheap and simple process for its manufacture from corncobs. In brief the process consists in digesting the cobs with steam a t about 135 lbs. pressure for approximately 2 hours, while distilling off slowly the furfural formed, and collecting i t as a dilute aqueous solution. The latter is put through a column still provided with continuous decantation in order to separate the furfural in the form of a 95 per cent solution. Just enough sulfuric acid (about 0.75 per cent of the weight of cobs) is added with the charge to neutralize the bases present, and water is added in such quantity that with condensed steam the water-cob ratio 30 minutes after digestion begins will be about 4:l. At the end of the digestion the digestor contents are discharged, drained, washed, and pressed to separate the cellulosic residue and liquor. The liquor contains some furfural which is recovered as a dilute solution to be used in subsequent digestor charges. (For further discussion see Fuifnral, p. 1175.)-U. S. Bureau of Chemistry, Washington, D. C. Manufacture of Phosphoric Acid by the Volatilization Process The investigations of the Bureau of Soils on the pyrolytic treatment of phosphate rock date back to 1912. This work was undertaken as one phase of the problem concerned with the development and utilization of existing and new sources of fertilizer materials. The volatilization method of treating phosphate rock appeared to offer possibilities as a means, first, of conserving our phosphate deposits through the utilization of low-grade and run-of-mine rock, and, second, of producing phosphoric acid as such in a form best adapted for making concentrated fertilizer. Volatilized phosphoric acid offers advantages over that prepared by the sulfuric acid method in that i t is initially of higher purity and concentration; i t can be more easily refined; transportation costs are lower; it can be used directly without concentration in the preparation of concentrated salts; and by crystallization it can be made to yield directly a higher grade product than can be produced by any other method. Recent laboratory investigations have shown that phosphoric acid can be almost completely volatilized from mixtures of phosphate rock and coke, with or without the addition of sand, a t temperatures of 1200° to 13OO0C. with the production of an unfused residue. Investigations bearing on the
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commercial possibilities of this low-temperature process are now in progress.-U. S. Bureau of Soils, Washington, D. C. Improved Catalyst for Ammonia Synthesis
'
The catalyst may well be called the "heart" of the synthetic ammonia process. The development of the first technically suitable catalyst material, by the Badische Anilin und Soda Fabrik in 1910, established the foundation for the ammonia industry and at the present time the properties of the catalyst are dominant factors in the determination of ammonia production. Experiments made so far show that no one metal possesses all the properties desirable in a practical catalyst. Distinct improvements have been effected, however, (1) by mixing certain active metals, and (2) by adding small quantities of apparently inert substances to catalytically active metals. During the war extensive investigations of the first method were made in English, French, and American laboratories. In these experiments the best results were obtained with a mixture made up of equal parts of iron and molybdenum. Since cheaper and better catalysts can be prepared by the second method of activation, this iron-molybdenum combmation has never been employed in the commercial production of ammonia. The results of experiments disclosed the fact that no single substance effected an improvement in the catalytic properties of iron even remotely comparable to that produced by a combination of two or more properly selected substances. The superiority of a properly selected multicomponent or composite promoter is evident from the following tests on three iron catalysts-one containing potassium oxide; a second, aluminum oxide; and a third a combination of both oxides. These tests were all made under strictly comparable conditions at 100 atmospheres, 450° and 5000 space velocity, that is, 5000 volumes of gas (N. T. P.) per hour per unit volume of catalyst. In these tests the iron catalyst containing only aluminum oxide gave 9 per cent of ammonia by volume in the effluentgas, while the one containing potassium oxide gave 4 per cent. When ~otassiumoxide and aluminum oxide in the form of potassium aluminate were added to the iron, the resulting combination produced a catalyst giving 14 per cent. Composite prcmoter combinations of other basic and acidic oxides were found to give desirable results. I t will not be possible to discuss the various forms of iron oxides which might be employed and their methods of preparation. I t is sufficient at this time to state that an artificial magnetite has been found to give the most satisfactory results. The problem of preparing an oxide is, therefore, one of iusing iron oxide and the promoter under such conditions that the chemical composition of the oxide mixture may be rigidly controlled. On
account of the great chemical reactivity of fused iron oxide it cannot be melted in any crucible so far developed. Many refractory materials have been investigated for this purpose, but all have been found to contaminate the molten oxide. The method finally adopted consists in fusing the oxide in a protecting bed of the same material. The electrical conductivity of the oxide is sufficiently great so that the material may be melted between water-cooled iron electrodes. Promoters are readily added to the iron oxide in this method of fusion, and all those substances which are known to react unfavorably can be carefully excluded.-Pixed Nitrogen Research Laboratory, Washington, D. C.
ERRATA Val. 2. No. 9. n. 733, first .~ a r. a n a ~ h . - T h efifth sentence should read as follows: "Of what use is our research, our study of technical trivialities, while souls are scorching. athirst for the sustenance which real knowledge can give?' p. 735, next t o last paragraph.-"It is useless to insist. t o be useless.
. . ."
. . ." should be, "It seems
No. 11, p. 1066.-TheLatin quotation should read: Usus DecimlJium numeforum. Mensurw & fiondcra diuidantur i n 10, perks ocguaks, b sing& decimae rursum in d i a s aequeles 10, quae i5n efunt ce?&simae lolizrs: A&ue herum singuhe ierum i n 10, quae firoinde iam erunt nillesimae totius.
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