CENTRIFUGE, LOOKIKG RASP,IN A MODERNS WEET P O TATO STARCH FACTORY TOWARD THE
Manufacture of White Potato Starch in the United States C. A. BRAUTLECHT University of Maine, Orono. Maine and in improving, standardizing, and stabilizing quality. From the potato-growing viewpoint, much can and probably will be done to increase the supply of white potatoes available to industry during the next decade.
Much has been done during the past few years to improve production of domestic white potato starch to a state where some factories now make a product equal to the best white potato starch imported, an aid to both American industry and agriculture. Judged from the relation of the white and sweet potato starch industries in Japan, and differences between the characteristics of white and sweet potato starches, there will probably be little harmful competition with sweet potato starch produced in the two factories in the South, if these two starches sell for approximately the same price and there is no marked difference in subsidies paid from public t a x funds. W i t h the improvement in the quality of white potato starch made in three niodern continuous process factories during the past year, more can be expected in reducing production costs of high-quality starch,
E
FFORTS on the part of some potato starch manufacturers during the past few years have led to the production of domestic potato starch that is equal to the best imported from Europe. Present trends indicate that with a specified quality of domestic white potato starch assured, the interest of users under normal economic condition will continue. Although the general potato starch situation in the United States is briefly referred to, the emphasis of this article is placed on a description of the three new continuous process factories built in Maine during the past two years. These plants, replacing batch process factories, together with improvements in some of the other white potato starch factories, have caused renewed interest in white potato starch production. 893
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Production of Potato Starch starch factories in Maine in 1934. From 1936 to 1939, inclusive, potato production in Maine was relatively low; alWhite potato starch was first made in Antrim, K. H., though there has never been a potato crop failure in Maine, in 1831 (11). Its production rapidly increased and spread. weather conditions were adverse for good crops, especially The U. S. Census Reports listed about 152 potato starch in 1938 and 1939. factories in 1860, only 3 of which were in Maine. Changes in the industry by 1900 led to a listing of 63 factories, 45 of Although sweet potato starch has been made for a long time in Japan, its domestic production in the United States which were in Maine. I n 1920 there were about 20 factories began in 1934, when about 140,000 pounds were produced a t in Maine, with a daily production capacity of less than 75 Laurel, Miss,, in a factory developed by members of the staff tons of starch (all in Aroostook County), with one active of the United States Department of Agriculture. Production factory in Minnesota. In 1940 there are 27 starch factories increased annually during the following years; it was about in Aroostook County with a daily production capacity of over 500,000 pounds in 1937 (IS) and 2,700,000 pounds in 1939. 150 tons of starch. The two new factories a t Houlton and the A second sweet potato starch factory was built in St. Francisnew wet-starch plant a t Mars Hill are the best equipped, emville, La., in 1939 (17). ploy continuous processes, and can make the best quality of starch, equal to the best imported potato starch. One factory White potato starch production has survived in Maine behas also made fine-quality white potato dextrin. There is one cause of the high yield of potatoes per acre and a high conactive factory in Minnesota, and there are two factories in Yew centration of acreage. With a normal production of about Brunswick near Aroostook County. A few new white potato 47 million bushels in Maine and with proper grading, 5 to 15 starch factories are contemplated in Canada and the United million bushels of cull or scrplus potatoes should be available States. for starch factories. The time has now also come, during a Domestic white potato starch is now produced only in period of high prices for culls and the growing of low-starch Maine and Minnesota. White potatoes can be grown in varieties of potatoes which are also less suitable as food, to every state, but Aroostook County has the highest yields per inaugurate the payment for all potatoes going into starch acre (150 to 600 bushels) and a total of about 35,000,000 to factories on the basis of weight, starch content, and a price 45,000,000 bushels. The state of starch‘production in Maine factor, instead of a variable barrel measurement with estiin 1933 was briefly stated by the writer (2). mated discounts, etc. White Dotato starch Droduction in Canada is being incieased (6). One Canadian factory has beenincreasingitsProductionsteadilY. Another is TABLE I. PERCENTAGE COMPOSITION (1) OF MAINEPOTATOES, 1938 CROP to bemodernized and production greatly increased. Starch Basis A report on starch in 1938 (15) recorded that A? D.ry X’ariety Ash N P S K Mg Ca received weight the potato starch industry in the United States Chippewa 6.00 1.80 0.19 0.22 2.60 0.13 0 . 1 1 10.6 57 was “confined almost entirely to the County of cobbier 5 08 1 . 7 0 0 . 2 4 0 . 2 4 2 . 2 0 0 . 1 2 0 . 1 1 13.5 59 Aroostook in M ~ ~ ~that ~ ,156 I to ; 501 million Green M o u n t a h a 4.70 1.50 0.22 0.09 2.20 0.12 0.11 15.4 68 Rural (smooth) 5 . 0 3 1.40 0 . 1 5 0.14 2.40 0 . 1 2 0.11 14.5 60 12.0 .... .... .. .. .... ..., ..., .... 60 pounds of white potato starch were produced in 14.8 64 the per year between 1929-30 and a T h e growing of Green Mountain potatoes, produced in Maine t o the extent of about 1933-34, of which 8 to 13 million pounds Were 70-75 per cent of the total potato crop in 1939, has shown a decrease. Present evidence, however. indicates t h a t it will be increased again in a few years. exported to the United States. F~~~71 to 137 million pounds of white potato starch were produced annually in Japan between 1930 and Potato flour, obtained by steaming potatoes under pres1934. Japan also produced 38 to 63 million pounds of sweet sure, is produced to a considerable extent in Idaho, and in one potato starch per year during 1930 to 1934. Production of factory each in California and Michigan (14). white potato starch in Germany, within the geographical limits as of 1930, was about 250 million pounds per year. Domestic potato starch production during the past six or The White Potato seven years has been about 10 to 25 million pounds. During Production of white potato starch of high quality requires the past few decades, annual imports of white potato starch a consideration of potato composition. The white potato have often exceeded domestic production. (Solanum tuberosum) is an underground stem tuber. The In discussing the modernization of the Maine potato starch sweet potato is a true root. For this reason, white potato industry, the writer stated (4) that there were 21 potato starch has slightly different characteristics which make it possible to obtain the purest form of commercial starch (almost 100 per cent pure). The tuber consists of anouter (corklike) and an inner skin, a cortical or fibrovascular layer, and flesh or pulp in form of outer and inner medullary layers of cells containing the starch granules. White potatoes have a percentage composition approximately as follows: water 70-80, protein 2, fat 0.1, ash 1.0, starch 10-30, cellulose 0.5, sugar 0.4. Weather conditions during the growing period, soil, quantity and kind of fertilizer, variety, etc., influence the composition greatly. Maine potatoes, where about one ton of fertilizer per acre is used, have a percentage composition on a dry-weight or moisture-free basis at harvest (1938 crop, wet season) as shown in Table I. STARCH TABLES
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INDUSTRIAL AND ENGINEERING CHEMISTRY
895
With present government acreage curtailment for food p o t a t o e s , farmers should endeavor to grow some potatoes directly for industry, on idle acres on which they must pay taxes, outside of River Water their seed and food acreage quota. I n this way they may also use e x i s t i n g equipment and facilities to obtain the - 3 h f t k i 4 Steve lowest unit potato production costs. Congressman Brewster recently indicated that the vast subsidies to special crops must Yaste Pulp Sua cease ( 5 ) . It is obvious that they cannot continue ind e f i n i t e l y , either through direct crop subsidy or through indirect subsidy by means of land reclamation or irrigation procedures developed with federal tax funds. The supply of cull or surplus potatoes which went into starch factories durS e t t l i n g Table ing the period 1924 to 1938 ranged from I --Agitator Table Taili6ge Waste 609,000 to 5,319,000 bushels, with an average of 2,200,000 bushels (10). I n 1934-35 a b o u t 3,884,000 bushels of StoraFe Pump Vaoum Dryer Starob white potatoes were Tank Filter Storage F l a w Sheet dumped, and there was a shrinkage of 3,329,000 bushels in FLOW SHEETOF A MODERN WHITEPOTATO STARCH FACTORY Maine (18). There has been no dumpIn addition, there are organic acids such as succinic, taring since that time. Dumping under present political and taric, citric, and ascorbic. Ascorbic acid (vitamin C) is the economic conditions must be strenuously prevented or avoided. principal vitamin in the potato. Amino acids, polypeptides, asparagine, sugars, pectin, and many other substances are Uses present. Tyrosine, an amino acid, is a source of much trouble in a starch factory because it forms insoluble precipiWhite potato starch, although produced and utilized on a much larger scale in Europe, finds extensive use in America tates with any iron compounds present in the water (9). in the following fields: as a size for cotton and woolen warp For this and similar reasons, the quality of water used in starch making is important; iron-free water especially is required threads, especially for fine counts, and as a thin finishing material with fine appearance in the textile industry; as a for a good-quality starch. Formation of precipitates on fine laundry starch; in making fine dextrins and adhesives fine brass, bronze, or silk sieves reduces production and increases cost. Compounds such as solanine are present durfor many purposes; in making glucose; as a bonding mateing sprouting. Freezing of potatoes causes a change of some rial in plywood manufacture; as a fine wall paper paste; as starch to sugar, which is lost in processing. Therefore, freeza size for fine papers; in making nitrostarch explosives which ing must be avoided, both in general and in factory potato have properties intermediate between nitrocellulose and nitrostorage. glycerin; in textile-printing pastes; in making soluble and
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INDUSTRIAL ZND EWGINEERING CHEMISTRY
VOL. 31. NO. 7
70 per cent of the starch present in the potatoes. With growing conditions during the crop years of 1938 and 1939 below normal and with the growing of more low-starch potatoes, recent relative yields havc been decressing. I n the factories using rotary or belt dryers, moisture content can be controlled, and starch is bagged with 14 to 20 per cent moisture, within limits specified by the consumer. It is now possible for all white potato starch makers to havc their products thoroughly examined, to have their potatoes tested for starch and adhering dirt, and to have the starch extracted and examined in an experimental unit to determine quality and quantity obtainable. In the new factories, using saw-tooth rasps, brush and jig sieves, protein-water separators, and fme regrind mills, yields have been greatly increased. Uhland engineers have been able to obtain over 95 per cent ol the starch present, in commercial units
(le).
Houlton Factories modificd starches, vegetable and cold-water glues; in making malt sugar used in brewing; as a cosmetic; in colloidal and perfume prcparatioas; as a binder in coal-dust briquets (poorquality starch); etc. In the food industry it is employed in bakeries for making special breads and cakes, etc.; in eonfectionery, as a thickener in soups and canned foods, in salad dressings, etc. Large granule size, relatise proportion of amylose and amylopectin, and phosphoric acid content impart to whitc potato tuber starch some desirable characteristics and a dcgrce of punty not possessed by other commercial graik, root, or pith starches. NEWYORKPRICES.Imported potato dextrin was quoted in Fcbruary a t 7.75 cents, nominal (1s). Although some domestic potato dextrin is made in Boston, no price is published. Domestic potato starch was quoted a.t 6.25 cents, nominal, and imported a t 6.5 cents, nominal. Sweet potato starch was quoted at 5.5 to 6 cents. The relatively high present prices are due to reduction of imports as a result of the European war. Corn and tapioca starch prices are usually about 2.5 to 3.5 cents per pound. Domestic white potato starch of good quality sold a t about 4.5 to 6 ccnts in 1935 and 1936, with the imported usually quoted at about 1 cent per pound higher. The starch imported from the Netherlands has had a preferential duty of 1.75 ccnts per pound, and the regular Lmport duty rate has been 2.5 cents per pound. The price of imported potato dextrin has changed little during the past six years. It has heen subject to a duty of 3 cents a pound, with a preferential duty to the Netherlands of 2.25 cents.
Factory Control In the old factory process there is no control of yield otbcr than an estimate of the numbcr of 11- or 12-peck barrels of potatoes ground or paid for and the number of pounds of starch obtained. Discounts are imposed for short barrels, very dirty or badly rotted potatoes, etc. From thcse two factors, yield in pounds of starch per barrel of potatoes is computed. This procedure involves relatively large errors, for in some cases the same volume of putatoes from one grower would have a t least 20 per cent more starch than that from anothcr grower, and moisture content of fmished starch in one lot would be about 10 and in aaothcr case about 20 per cent. Yields by the old process are usually between 50 and
Two new modern factories were built in Houlton, Aroustook County, in 1938. One of them bas a capacity of about 16 tons of starch per day on a continuous operation basis, using potatoes with about 16 per cent starch; the production capacity of the other is about 10 tons of thc highest quality starch, on the same basis. The details of process and equipment differ somewhat, but a description of one of the plants will sbow the use of modern methods in this field. The procedure in the second factory is briefly outlined. Electric motors of 220 volts supply all power, which is furnished by the looal public service company. A locomotive type boiler of about 150 horsepower is used to supply steam for the drycr and unit building heaters a t about 150 pounds pressure. Auxiliary equipment and condenser arc near by. A stoker, with steel hopper, supplies coal to the boiler to maintain a uniform steam pressure. Water is obtained from Pierce Brook through two 5-inch lines connected with direct-connected centrifugal pumps, one with a 10-horsepower motor, the other with a 7.5-horsepower motor. Public utility water supply is also available and is used on some orders. PROCESS AND S n m x i EBWIPMEHT. Potatoes are received from trucks onto runways over the partitions of five potato hoppers and are dumped. From the hoppers or storage bins the potatoes move by gravity tbrough gates to a plank sluice trough, attached to the wall and fitted with five &inch pipe stone traps, and tbcn by gravity to the first of two washers. The first washer has a barrel-drum section a t the entrance end, attached to the heavy shaft to which hardwood paddles are also attached. The paddles force tbe potatoes countercurrent to a stream of water to the exit end of the first waber, from which they are removed by a conveyor to a necond washer of similar construction but with no barrel section. The barrcl-drum section has a cleaning action due to some centrifugal motion of the potatoes against the inner wall. The washed potatoes are moved from the clean or discharge end of the second washer by a short inclined bucket elevator to the small rasp hopper, with an overflow return to the second washer. A small screw-conveyor removes potatecs from the hopper to the Jahn saw-tooth rasp with one bearingblock. Below the drum is a perforated steel plete through which the starch suspension and pulp passes. The rasped potato pulp and suspended starch, with its complex mixture of prot,eins, amino acids, polycarboxyl organic acids, and
JULY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
other compounds in solution (potato skins of corkliie nature, cellulose fiber from cell walls, etc.) is passed through a rotating coarsemesh wire sieve, to remove coarse particles which would interfere with a protein-water separator set ahead of the first sieves. The pulp then flows to a sump where it is treated with about 0.5 pound of sulfur dioxide per ton of starch, the gas flow being measured by a rotameter. The gratings mixture is pumped by a centrifugal pump, to a No. 1 Uhland protein-water separator (a continuous horizontal centrifuge with imperforate conical bowl and continuous spiral-ribbon starch remover). Here the starch, cellulose, and skins are separated, cut loose, and resuspended in a small stream of thin starch milk or fresh water. To economize on water, thin recovered starch milk which does not contain too much impurity is used wherever possible. The interior parts of a protein-water separator are constructed of bronze and copper, and must be kept cleau, have proper clearauces, ete. A direct-connected %horsepower motor furnishes power. The waste protein-water is run into a concrete floor channel covered with perforated steel grids, then to a public sewer. The suspension of solid material, with the starch, is then pumped by a centrifugal pump of about 2 horsepower to a starch-extraction sieve set. The pulp from this set is reground in an abreaive stone mill and is then pumped by a 2horsepower centrifugal pump to two jig (shaker) sieves fitted with frames having 100-mesh wire (7). The reground and extracted pulp from the second extraction sieves is wasted to the sewer. The thin, crude starch milk is pumped by a 1-horsepower centrifugal pump to the shaker sieve in tho first extraction unit for dilution purposes. All starch milk, with some fine fiber, then flows by gravity to the second No. 1 Uhland protein-water separator. The protein and wash water are wasted. The starch is resuspended in fresh water and thin, clean starch milk, and is then pumped by a centrifugal pump through a 2.5-inch pipe line to the adjustable-pitch wood-plank tables on the second Aoor. Here it is divided in head boxes to four sets of table units in small streams; the heavy starch settles out, and the very fine starch flows hy gravity from the tables to two shaker sieves on the first Aoor. These tailing sieves are fitted with section gutters and 200-mesh silk bolting cloth. The starch is thinned over the bolting cloth, with water to remove fiber and slime, which pass off the sieve to waste. The starch milk which pass
897
through the sieves is pumped to and divided hetween the two protein-water separators. The tables are flushed with a heavy stream of water from 6inch pipe fines into a pair of concrete starch-storage vats, to yield a density of 5-7' BB. (1.03-1.05 specific gravity) as determined by gravity spindles. From these vats the starch ia pumped to and passed through a relining shsker sieve with a 200-mesh bolting silk, and is then pumped to a 40-inch centrifuge, where the starch is dewatered to about 40 per cent moisture content. Starch milk is circulated to the centrifuge by by-passing some starch milk back to the clean starch storage. The filtrate and decautate flow to a sump and are pumped to the first protein-water separator. ~~
TARLE 11.
~~
POWER
~
~~
REQUIREMENTS
Potato washem. olemtor. oonveyoi. map. and coarse material separator First protein-water separator Primary brush and shakei sieves Pulp rognnder Second prote~n-wstcraephrator Refining sieves Pumw for brook wiater fox washins equipmmt, fur boilcr water. washer. et$. Centiifuee, perforate basket Starch elevator, vet. long Starch cievstor, dry, sbort
vat sgiteturs
Stmch hsmrner mill Starch aiitcr Centrifussi pampa for starch s u ~ p e o ~ i u r ~ s
a5 h. p 15 3 10 13 3
I9 IS 3 2
5 10
3
nrrrnr
Tothi
162 (12 kv.)
The four outlets for process wastes are the two proteinwater separators, the table-tailings refining sieve set, and the reground pulp extraction sieve set. These possible sources of starch loss are frequently tested by examination of centrifugal sediment, which is obtained in a laboratory centrifuge. The starch cake in the dewatering centrifuge is plowed off into a trough below. It is then conveyed by a spiral conveyor to a vertical bucket elevator which raises it to a hopper above the dryer on the second floor. On leaving the lower exit end of the starch dryer, the starch is raised by a bucket elevator to a h a m e r mill. After p w i n g through themill, it is passed through a sieve, then to a bag hopper, and is filled into 200-pound kraft-lined burlap bags for storage. The control carried on a t the factory is for density of starch suspensions, for materials flowing to the protein-water separator, for tabling concentrations, etc. Starch is tested for moisture content, whiteness (reflectanw), specks, pH, viecosity, etc. Some of the chemical testing of the water used (which is important) and of potatoes and starch is carried on in chemical lahoratories elsewhere. At such laboratories the finished starch is again tested for water, ash, solubles, viscosity, pH, reflectance (8). specks, granule size, starch by hydrolysis, p a t e quality, bacteria, etc. The approxlmate power requirements of the various units, using about 11,000 pounds of potatoes equivalent to about 1540 pounds starch with 17.5 per cent moisture per hour is indicated in Table 11. The total metered power consumption, for processing, averages about 162 horsepower for about 5.5 tons potatoes (11,000 pounds or 170 bushels or 62 barrels) with 12 to 16 per cent starch. This corresponds to ahout 0.70 kw.-hr. per bushel of potatoes processed or for 7 pounds of starch, or 0.105 kw.-hr. per pound of starch with 17.5 per cent ROTARY V.&CWMF I L T EUSED ~ rx A NEW POTATO STARCH fan on^ moisture.
INDUSTRIAL AND ENG;INEERING CHEMISTRY
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The public utility industrial-electricity power rate in Houlton is about 1.7 cents per kw.-hr. Power cost is therefore about 0.18 cent per pound. Some reduction is effected by a lower rate for off-peak load current at night. Lighting cost is about 0.02 cent per pound. Direct labor is approximately 0.07 cent per pound. The other new starch factory in Houlton differs in having a different water, heat, and power supply setup, large potato cellar instead of hoppers, with a water-conveying trough with stone traps, conveyor to raise the wet and partly washed potatoes to the washer, concrete washer with steel grid washwater outflow and with drip sections, washed-potato bucket elevator discharging into a half-ton steel hopper, spiral feed screw to move potatoes to the rasp at a controlled rate, and a small high-speed rasp (1500 r. p. m.). The raspings, after chemical treatment, are pumped to the extraction sieve set, with a fine stone mill to regrind partly extracted pulp, then to a continuous horizontal protein water and starch separator, treating vat, refining sieve, concentration control vat, and to polished concrete tables with wood separators, more wash vats, vacuum filter, bronze-wire belt dryer, bolter, and bag filler. The pumps in the wet-starch room are of the adjustable plunger type. This factory is equipped to make separation of starch on the basis of granule size, when desired. Wet-Starch Factory The factory at Mars Hill is the first wet-starch factory in the United States. Potatoes are received at two intake doors onto an interior platform, dumped from barrels onto one of two elevating conveyors, which raises them over the near side of a concrete hopper wall and drops them onto a distributing conveyor or into one of two concrete hoppers with sloping bottoms. On the far side of the hopper wall is the wet-starch room. This wall is essentially a concrete partition with boarding above to the roof, to prevent dust from the potato hoppers from entering the wet-starch room.
VOL. 32, NO. 7
sieves is wasted into the near-by stream; starch milk is pumped to one of two covered starch-milk tanks with agitators; the density of suspension is adjusted, and then the starch milk is pumped to a dewatering overhead-suspension centrifuge. The impure starch cake is plowed off into steel boxes under the centrifuge, which are raised up an incline to a truck-loading platform and trucked to Houlton for purification and drying. The capacity of this plant is equivalent to about 6 tons of starch with 40 per cent moisture per 8-hour shift. A proteinwater separator will probably be installed to carry out partial purification. Power and water requirements and auxiliary equipment are similar to those in the Houlton factory. White Potato Starch Production Costs In a modern white potato starch factory there are direct labor, power, and drying costs, the potato cost which varies (about 65 cents per barrel in 1939-40), packaging expense (about $1.80 to $2.50 per ton), and the usual overhead costs, including several kinds of taxes, rents, fire and liability insurance, interest on investment, lighting at about 35 cents per ton of starch, communications charges, administration, indirect labor, office expense, potato buying cost, depreciation, repairs, oil or coal for fuel, lubricating oil, building and equipment maintenance and replacements, metered and purchased water and electricity, sales and collection expense, bad debt charge, transportation, advertising, factory s u p plies, etc. Consideration of these economic factors of modern white potato starch production were outlined by the writer in 1934 and 1936 (3). The lowest approximate general cost of highest quality white potato starch per pound on the New York market is shown in Table 111. Wide variations in the starch content of potatoes and consequently in yield of starch will cause considerable variation. Supply of potatoes and rate of continuous operation also influence cost to a great extent. Lit erature Cited
TABLE111. APPROXIMATECOSTOF ONEPOUND OF WHITE POTATO STARCH (IN CENTS) Potatoes, including buying cost Process power Drying Direct labor 1,iaht
T Z e s , rent, insurance
Interest on fixed and working capital investment Indirect labor Packaging Depreciation and contingent expense Building a n d equipment maintenance ~. Re airsLugricating oils, chemicals, factory supplies Sales cost and advertising Transportation of eome potatoes Transportation of starch Research, control, development Amortization of fixed cauital Water purchased Faoto; hygiene and safety Office expenses. accounting, office supplies, contingencies, communication, travel, etc. ~
1.90 0.16 0.50 0.07
a a2 0.03
0 15 0.01 0.012 0.09 0.01 0.01 0.01 0.30 0.05 0.50 0.01s 0.03 0.01 0.01
0.30 4.190
Estimated gross profit a t 15 per cent Approximate lowest cost of high-quality domestic white potato starch in New York
0.629 4.819
The potatoes are admitted from the hopper through ports, one a t the lowest part of each concrete hopper, to a waterconveying trough with stone traps. Water conveys the potatoes to the first of two concrete washers, then to the second washer, and finally by bucket elevator to a rasp hopper. The gratings are diluted with water, treated with sulfur dioxide, and pumped to a pair of shaking extraction sieves. Pulp not passing these sieves is reground and pumped to the second extraction sieve set. Pulp not passing the second set of
(1) Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 5th ed., 1935. (2) Brautlecht, C. A., mimeographed letter to potato growers and starch manufacturers, Sept., 1933. (3) Brautlecht, C. A., Ibid., 1934; Chsm. Industries, 38, 465 (1936). (4) Brautlecht, C. A., Rept. New England AESOC. Chem. Teachers, 41, 59 (Dec., 1939). (5) Brewster, R . O., Bangor Daily News, Aug. 5 , p. 10 (1939). (6) Canadian Census, Ann. Bull., Manufactures, Pt. 11. (7) Jahn & Co., personal communications, April 17, 1935; Jan. 18, March 2, April 24, 1937; May 9, June 3, 1938. (8) Keane, J. C., and Brice, B. A,, IND. ENQ.CHEM.,Anal. Ed., 9, 258 (1937). (9) KrBner, W., 2. S p i r i t u s i d . , 60, 39 (1937). (10) Maine Crop and Livestock Rev., 1938, 14. (11) New England Farmer and Horticulturist J . , 10, 141 (1831). (12) Oil,Paint Drug Reptr., Feb. 5,1940. (13) Paine, H. S., Thurber, F. H., Balch, R. T., and Richee, W. R., IND. ENG.CHEM.,30,1331 (1938). (14) Roger Bros. and Falk Products Co., personal communications, 1934 and 1938. (15) Spicer, R., U. S. Bur. Foreign and Domestic Commerce, Report, June, 1938. (16) Uhland, W., personal communications, May 22, Aug. 20, 1935; Dec. 29, 1936; Feb. 9, June 17, Aug. 10, 1937; May 5, June 15, 1938; April 27, Oct. 13, 1939. (17) Warriner, J., personal communication, June 28, 1939. (18) White, C., personal communication, Jan. 20, 1936.
