I / '
Production of Clean Gum Rosin W. C. SMITH Bureau ofChemistry and Soils. Washington.
UM rosin is a vitreous transparent. solid having a color ranging from pale yellorr to reddish brown when viewed through sniall lumps. It consists of about nine parts isomeric rosin acids having the formula CdLOOsand about one part of neutral or unsapotiifiablematter, together with a very S N quantiry ~ of impurities. If a sniall lump of gum rosin is carefully examined with the unaided eye or through a low-power lens, srnall pirtieles of matter \rill he seen uniformly scattered throiighout tlre ma These small particles of visible extraneous matter are cornntonly referred to as "dirt." All gum rosin as now coniniercially produced contains some dirt. Usually the quantity present. is small (less t,han 0.1 per cent) and is not not~iceiriile except on close examination. Rpsins containing such small quantit,ies of dirt are rcferrcd to in the Wade as "clean." Yigure 1A shows a phot.omicrograpli ai a lager of so-called clean rosin 0.125 inch (0.32 cm.) tliick. The sire of particlcs of dirt can he determined from the superimposed scale (t,lie smallest divisions represent 0.1 nim. or about 0.004 inch). IIowever, for the purposes of this discussion only rosin \yhicli is pract,ically free from dirt will be ternred clean. 408
D. C.
Under the presmt nietbod of manufacture it is not possible to produce a clean rosiri and sometimes, owing to carelessness on the part of the operator, the rosin may contain suflicient dirt to cause it. to be unsuited for certain uses and thereforr he rejected by the purcliaser (shown hg the size of part.icles of dirt in Figure 111). The dirt in rosin also reduees its briglitness and transparency and thus tends to lower its grade. Since the recent appearance on tile markets of the higher grades of wood rosin, which may properly be called clea,n, the consumers of gum rosin are slrorving a tendency to give preference to better strained gum rosin. Replies t,o a recent questionnaire sent out by the Rureau of Chemistry and Soils to a nuinber u i the larger users of rosin indicated in almost, every instance the desire for a rosin cont,nining a ininimuiii of dirt. Aii insight into the source and nature of this dirt may b e gained by considering tlre method by wlrich gum rosin ismade. The oleoresin af the pine, which constitutes the raw material of rosin, is obtained by wounding or chipping the tree and collecting the oleoresinous emdale or gum in an open reccptacle or cup hung on the tree below the wound. Tlie contents of the cup arc usually removed once a month. Along with
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microscopically. The smallest diameter of particle measured the gum certain foreign matter is collected in the cup-chips was 0.003 mm. (0.00012inch) and the largest 0.125mm. (0.005 falling in when the wound is renewed, bark and needles falling inch). A microscopical examination of another sample of dirt from the tree, rain water running down the tree into the cup gave almost the same results, the minimum and maximum and carrying with it dust and water extractives from the bark, diameters of the particles being 0.03 mm. (0.0012 inch) and dust blown in by the wind, insects, etc. When the cups are 0.114 mm. (0.0045 inch), respectively. As will be described emptied or dipped, part of the water is removed by decantalater, the unidentified brown matter was found to be obtained tion or pouring off, but it is not possible to remove the other from the water-soluble substance present in the water in the foreign matter or ''trash" a t this time. The gum containing gum or extracted from the trash during distillation. the trash and water is then subjected to steam distillation in The microscopical examinations were made by G. L. order to remove the spirits of turpentine. A t an early stage Keenan, of the Food and Drug Administration. the distillation is interrupted at some plants, the still is opened, and the larger particles of chips, bark, needles, and other foreign matter which may be floating, are removed by Making Clean Rosin skimming. During the greater part of the distillation the In order to produce a clean rosin, three methods may be bark, chips, and other trash in the still are being extracted followed: and partly broken up by the water and steam used in distilling. It is not until toward the end of the distillation that the pieces 1. Removal of the dirt from the rosin. of bark and chips become so coated or saturated with rosin 2. Production of a gum initially free from all foreign matter, that water cannot penetrate and remove soluble matter from including water. 3. Removal of all dirt, including chips, bark, needles, and them. When all the turpentine and water have been removed, water, from the gum before distillation. the distillation residue or rosin which is in a fluid state and the trash and dirt which were not removed by skimming are Dirt can be removed from rosin only by filtration or strainlet out of the still through a large gate valve onto a set of ing since it will not settle out completely even on prolonged nested strainers resting over a large vat. The top strainer standing. The success of filtration or straining depends on is a coarse-mesh wire sieve and retains the larger particles of the viscosity of the rosin and the nature of the filtering trash. The second strainer is of 40-mesh wire (apertures medium. To reduce the viscosity to a suitable extent, it approximately 0.5 mm. or 0.02 inch square), and retains much is necessary either to subject the rosin (31) to relatively high trash that Dasses through the top strainer. The bottom temperatures or to dissolve it in a strainer is bf 0.25-inch- (0.64-em:) suitable solvent. Cotton batting will mesh wire and is covered with one not completely remove dirt from or two layers of c o t t o n b a t t i n g . All gum rosin now prorosin, which is usually filtered or The hot liquid rosin passes through strained a t an initial temperature of duced c o n t a i n s a small the batting; therefore, the quantity about 155OC. (311OF.). The filtraand maximum particle size of the dirt q u a n t i t y of dirt. The tion through batting must be rapid remaining in the finished rosin are methods by which a clean because below 150" C. (302" F.) the dependent on the porosity of the rosin may be produced are viscosity rises rapidly, and the rosin batting as well as on the quantity of (1) removal of the dirt will not go through the batting or fine dirt in the unfiltered rosin. Howfilter. The use of paper or other from the rosin, (2) producever, the batting may become rupmaterial which will retain all the dirt tured and in this case the maximum tion of raw material (gum) materially decreases the rate of filtrasize of the particles of dirt is limited initially free from foreign tion and necessitates an increase in by the mesh size of t h e m i d d l e matter and water, and (3) the temperature a t which the filtrastrainer. removal of foreign matter, tion must be carried out. Suitable The dirt in rosin is not soluble in means of keeping the liquid rosin a t including water, from comtoluene and may be easily removed by that temperature must also be prod filtering a toluene solution of the mercial gum before distilvided. Laboratory experiments show rosin through paper, asbestos mat, l a t i o n . A t present t h e that, when the temperature is raised or other suitable medium. When third of these methods apas high as 190" C. (374" F.), the rate the toluene is removed from the filpears to be the most pracof filtration is still too slow and in adtered solution by distillation, the redition the r o s i n becomes darker ticable. None of the many covered rosin is clear and free from colored if exposed to the air. KO visible particles of dirt. p r o c e s s e s patented since references to the use of this procedure The general nature of this dirt is 1835 is found to produce a have been found. There is room for indicated by a microscopical and gum from which a truly further investigation along this line, chemical e x a m i n a t i o n of the dirt clean rosin can be made. such as filtration of the rosin a t high taken from a sample of rosin contemperatures under p r e s s u r e and Laboratory tests show that t a i n i n g a n e x c e s s i v e quantity. through arbestos fiber mat or similar The chemical examination showed it is necessary to remove material. the following materials (in per cent from the gum not only all Rosin is readily soluble in several by weight) : the solid extraneous matcommon o r g a n i c solvents. The Combustible (organic) 75 ter, but also all the water, cheapest of these, from the standSoluble i n aqua regia (metallic oxides) 10 Other inorganic, principally sand and point of first cost, are the mineral which contains certain clay 15 oil distillates. For a long time the solids i n s o l u t i o n . This rosin from batting dross has been The dirt consists of mold filaments aqueous solution must be and spores, pollen grains, insect derecovered by adding light mineral oil, removed before filtration bris, stone cells from tree bark, frageffecting solution of the rosin by of the gum or immediately heat, filtering the solution from the ments of silica and irregular brown thereafter. masses which could not be identified cotton and dirt, and removing the
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of which originated in France. The majority of these methods (56) consisted in collecting the gum in pots fitted with covers to prevent contamination with rain water and falling particles, and also to cut down the evaporation of spirits. Apparently they have not been found commercially feasible. From the standpoint of purity of the gum the method of the American, Gilmer (18), developed in 1910, and that of the Italian, Bellini (SS), developed in 1928, may have some promise. Both methods give a gum which is almost free from trash and water and which yields a greater percentage of turpentine and a higher grade of rosin than is possible from gum collected in a n open cup. On account of higher costs and lower yields of gum per tree, neither of these methods has replaced the open cup method.
Cleaning Commercial Gum
FIGURE 2.
DENSITY OF GUMS
mineral oil by distillation. The dirt may be removed from rosin in a similar manner. Usually the cleaned rosin will be more-highly colored than the original. However, if the color ,of the dirty rosin is due chiefly to iron, and alcohol is used as the solvent, there may be an improvement in the color of the cleaned rosin The use of alcohol as solvent has been advocated (30). The solvent method is expensive, and it has not been determined that the improvement in the rosin would justify the additional cost. In 1917 Donk (lo), of the Bureau of Chemistry, was granted a public service patent on a process of producing high-grade rosin from low-grade rosin by distillation under relatively high vacuum (pressure, 20 mm. mercury). This process, which gives as a distillate a product that is light colored and clean, has not been utilized by the gum industry; however, it is understood that a process utilizing the same principlei. e., the distillation or rosin under reduced pressure-has been used successfully by the wood rosin industry. The distillation of rosin under reduced pressure is employed in processes covered by recent United States patents (18, $0, 21, 24, 26).
Collecting Clean Gum from the Tree The production of a gum initially free from foreign matter may be considered as the ideal toward which producers should work. However, a t present there seems to be little chance for the general production of perfectly clean gum. A number of methods for producing a clean gum have been t,ried, most
I n view of the difficulties in removing dirt from rosin and the impracticability of obtaining thoroughly clean gum directly from the tree, it seems that the best chance of success in producing clean rosin is offered through the removal of the foreign material from gum collected under conditions insuring minimum quantities of extraneous material. The idea of purifying or cleaning gum is by no means novel. On August 27, 1835, a United States patent was granted to Isaiah Jennings of New York for “a process of and apparatus for the distillation of spirits of turpentine and other analogous articles.’’ His method in part consisted of diluting the gum with turpentine, warming, and allowing the heavy foreign matter, sand, water, etc., to settle to the bottom of the tank. Bark and chips, which float, were removed. The diluted gum was then decanted. Since that date, a large number of patents have been granted in the United States covering processes of and apparatus for cleaning gum. French patents have been equally numerous. It is a common practice in France (5) to purify the gum by a method similar in principle to that of Isaiah Jennings. To the writer’s knowledge no American distiller uses any of the patented processes for cleaning gum. However, gum which has been treated by the recently developed Cline process (8) is now being offered to the industries without a preliminary separation into turpentine and rosin. Cline’s process consists in removing the trash from the gum by straining and then removing the water by distillation, the oily portion of the distillate being returned to the gum. The French work on cleaning gum has already been presented in considerable detail (56), and space does not permit a discussion of the American patents (1, 2, 4-9, 11-16, 19, 22, 23, 25, $7, 28, SW, 59, 40, 41) involving gum cleaning. The processes covered by these numerous patents may be grouped into two general classes: FILTRATION. Gum is usually liquefied by heat and/or addition of solvent and then passed through sieves, metallic cloth, filter cloth, or cotton batting. GRAVITYSEPARATION. This process generally consists in liquefying the gum and reducing its densit below that of water by heat and/or addition of turpentine, andJTallowing it to stand. Water, the density of which may be increased by the addition of common salt or other salts, and other heavy impurities settle to the bottom of the receptacle and are drawn off; the bark and other light impurities float and are removed from the surface; and the purified gum is drawn into another receptacle with or without filtration.
Most of the American methods for gum cleaning are based on filtration. The usual method of effecting the filtration was by gravity-i. e., by allowing the gum to pass through the filters by the pressure of its own weight. In several of the French processes, additional pressure was used to facilitate the operation. This additional pressure was obtained by
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suction or partial vacuum, filter presses or hydraulic pressure, pneumatic or steam pressure, and centrifuging. An interesting development in gum cleaning involves the separation of the solid or crystalline portion of the gum and treating it separately. Autrey (2) removed the liquid portion of gum by decantation and melted the solid portion by heat. The melted gum was treated with fuller's earth and filtered through cotton batting. Rosin made from the gum was also filtered through batting to remove foreign matter. Barraud (3) suggested the addition of spirits of turpentine to the cold gum followed by thorough stirring and rapid filtration, the solid portion being subsequently treated with heat. Palkin and Clark (299) extended this work to include the fractional crystallization of the solid or crystalline portion of the gum. Although their process was not developed primarily for this purpose, the rosins from the various fractions, in addition to showing an improvement in grade, contained much less dirt and were brighter than was the rosin produced from the original gum. The addition of turpentine facilitated the separation of water, and recrystallization aided in dragging down the fine particles in suspension. Filter cloth alone was used as the filter medium. With the use of a less porous substance a truly clean rosin can be made from gum treated in this manner. The express purpose of a large proportion of the patents cited was the removal of chips, bark, etc. There were no specific claims that the processed gum would produce a rosin free from all dirt. It is believed that none of the processes mentioned will produce a gum from which absolutely clean rosin can be made. All samples of commercial gums and gum rosin examined in this laboratory contained suspended matter. Experiments in this laboratory on the gravity separation method have shown that even on prolonged standing, particles of dirt remain in the gum and consequently in the rosin made therefrom. As shown in Figure lC, samples of French rosin made from gum treated by the gravity separation process were found to contain finely divided suspended matter. The majority of the filtration operations mentioned were carried out with wire gauze or metallic cloth alone. However, some also used filter cloth and others cotton batting. It is evident that it would not be possible to use wire gauze of sufficiently fine mesh to retain the smallest particles of dirt. Palkin and Clark found that filter cloth would not retain the finest dirt. Autrey, after adding fuller's earth to the gum and filtering through cotton batting, found it still necessary to use batting for filtering the rosin. The size of particles of dirt that will pass through cotton batting along with the rosin has already been shown. It is well known, however, that as filtration progresses, a mat of the retained particles builds up which acts as a iilter medium and thus the effectiveness of the filtration is increased. A sample of cotton batting through which a charge of rosin had been filtered showed that about 15 per cent of the dirt retained by the batting passed through a 230-mesh sieve which had nominal openings of 0.062 mm. (0.0024inch).
will probably average about 8 per cent and the trash about 3 per cent of the crude gum by weight. There is also a variation in ratio of turpentine to rosin produced from different gums. The Kava1 Stores Station a t Olustee, Fla., found that the weight of the rosin is about three and a half times that of the turpentine. The gum which adheres to the tree and hardens, known as "scrape" or "gum thus," contains less foreign matter and turpentine than does the gum in the cup. The ratio of turpentine to rosin in scrape is only about one-half that of normal gum. If gum is allowed to stand for a long time, the crystals settle by gravity to the bottom of the container. The lighter part of the gum will have a higher percentage of turpentine, sometimes consisting of 35 per cent spirits and 65 per cent rosin. The supernatant liquors containing such high percentages of turpentine are lighter than water; i. e., the density is less. Fortunately the density of freshly produced gum is greater than that of water, otherwise the gum would be floated out of the cup by rain water. Heavy rains often cause a loss of gum either by splashing the gum out of the cup by its impact or by filling the cup with water and causing the fresh gum to float out of the cup before it sinks in the water. If the resin acid crystals in the gum are redissolved, there will be obtained what may be considered a solution of resin in spirits of turpentine. The mixing of turpentine with rosin or with gum does not entail a volume change. The density of a gum a t a specified temperature will therefore depend on the proportions and the densities of its components. The coefficient of cubical expansion of gum from 0" to 100" C. is almost uniform and is greater than that of water. This is the reason why a gum which at 20" C. is a little heavier than water will, when heated to 100" C., be lighter than water. The change of density of longleaf and slash pine gum with temperature and dilution was determined on samples obtained from the U. S. Forest Service. The results of these determinations, together with the density-temperature curve for distilled water, are shown in Figure 2. The change of density of French pine gum (58) with temperature and dilu-
Properties of Commercial G u m For a better understanding of the problems encountered in gum cleaning, it seems advisable to present certain additional facts concerning commercial gum. The gum as it exudes from the tree is a clear, almost colorless and somewhat viscous solution of rosin acids in turpentine. On reaching the cup, owing to loss of turpentine by evaporation or to isomerization of the acids, crystals of the acids begin to appear in the mass. By the time the cup is ready to be emptied, the gum is a pasty mass, made opaque by crystals and containing the foreign matter previously mentioned, which varies considerably. The water content
411
FIGURE 3. ENGLER VISCOSITY OF GUMS
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tion follows closely that found for American gum. The densities of both the turpentine and rosin of the French gum are higher than that of the turpentine and rosin from the slash and longleaf pine gum. The viscosity of gum is dependent largely on temperature and percent4 age of spirits of turpentine or its concentration. The nature and proportions of the components of the turpentine and resin acids also have an influence. The data shown in Figure 3 were obtained from the same samples on which the density determinations were made.
Experiments in Gum Cleaning Preliminary tests on gum cleaning at the still of a naval stores operator in Alabama, and subsequent work on cleaning heated gum (1) by simple filtration using the equipment extensively used in France in which the melted gum was filtered through wire gauze, cotton batting, and cotton cloth, and ( 2 ) by gravity, served to emphasize the difficulties of satisfactorily cleaning American gum which contains more chips and dirt than does French gum. The gum filtered through the wire gauze of the French equipment produced neither a clean rosin nor a rosin of higher grade. The use of cotton batting or cotton cloth did not remove the finer dirt and in addition materially reduced the rate of filtration. In laboratory experiments to develop a feasible process for completely removing the dirt from gum, filter cloth, cotton felt, or canton flannel alone were found to be unsuitable for the purpose. The use of filter aids such as Filter-Cel fuller’s earth, and bentonite, improved the filtration but did not insure the complete removal of the dirt from the gum. To remove the finest solid particles it was necessary to use a substance with a porosity not greater than No. 1 filter paper or a well-made mat of asbestos or cellulose fibers. .It was also found that, when the water which gum usually contained was removed and the water-free gum filtered through filter paper, a clean and bright rosin was made on distillation, but gum filtered in the same manner without the removal of the water made rosin containing considerable fine dirt although the filtered gum contained no visible solid matter or dirt. In order to determine the effect of this water, varying quantities of “water” which had been removed from gum and then filtered through paper were added to portions of filtered anhydrous gum. Rosin was then made from the gum. The quantity of dirt in the rosin was approximately proportional to the quantity of filtered “water” added. Rosin made from the anhydrous gum is shown in Figure 1D. Figure 1E shows rosin made from filtered gum to which 8 per cent of the filtered “water” was added. A microscopical examination of this dirt showed it to be similar to the unidentified brown masses previously referred to as being present in the dirt extracted from rosin. An examination of several samples of filtered “water” from gum showed that they contained 0.3 to 0.5 per cent of soluble solid matter. Tannin was found in all samples. The freshly filtered “water” which apparently contains colloidal matter will, on standing, soon show a sediment or precipitate. When the “water” containing the dissolved solids is evaporated during the distillation, the solids remain in the rosin. Very little of the matter originally soluble in water is soluble in rosin, and after the stilling process, when it has been precipitated in the rosin, the greater part of it is no longer watersoluble. This water-soluble matter is probably obtained chiefly from the bark, since bark is very readily leached by
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water and the extract produced is similar to the water found in gum. The writer has not found tannin in the washings of fresh trash-free gum collected in a manner to prevent contamination with water running down the tree. The ease with which bark is extracted by water even during distillation, and the effect of this extract in the gum on the color of the rosin made therefrom was noted by Schorger (34). The effect on the cleanliness and grade of the rosin made from gum containing “water”is discussed by Vezes and Dupont (37). They state that the “water” in the gum causes the rosin to become turbid and gives it an aspect called poivrd or peppered. They also state that the tannins in the “water” may lower the grade of the rosin. The deleterious effect of trash in gum is generally recognized by producers. No reference has been found as to the quantity of dirt introduced into rosin by bark. I n order to obtain some definite idea 8s to its effect, 3 per cent of pine bark in solid pieces, which had been previously washed free of adhering fragments and dust, were added to anhydrous filtered gum. After distillation of the gum the bark was apparently intact, but the rosin contained excessive fine dirt even after being filtered through two layers of batting. In addition to adding dirt to the rosin, the bark also increased its color and therefore lowered its grade slightly. The quantity of dirt introduced into the rosin by the bark may be estimated from the photomicrograph in Figure 1F. Hall (17) was of the opinion that the water-soluble material in gum exudes from the tree along with the gum and is not extracted from the chips and bark. He agitated crude gum with steam which was allowed to condense in the same vessel. This extract was concentrated by distillation. The distillation residue gave no test for tannin but gave certain tests for carbohydrates. It is probable, however, that the small quantity of tannin usually present had been hydrolyzed during the distillation with a liberation of substances which reduce Fehling’s solution. From the data available it is evident that, to produce a clean rosin from commercial gum, both the solid extraneous matter and the water containing dissolved solids must be removed completely. A simple filtration of the gum will not remove the “water,” and the usual gravity separation, although it may remove all the “water,” does not remove the fine solid matter which remains suspended in the diluted gum.
Laboratory-Scale G u m Cleaning The water must be removed from the gum before filtration or immediately thereafter because some of the solids in solution in the water soon begin to precipitate. The removal of the water before filtration by refluxing it, trapping it, and returning the turpentine to the gum was found to discolor the gum and degrade the rosin. The removal of the water before distillation was successfully accomplished by diluting the gum with sufficient turpentine to bring its content to about 30 per cent, maintaining a t 95’ C. until solution of gum was complete and then drawing off the water or decanting the liquefied gum. The separated gum was then filtered through filter paper. The dilution of the gum with turpentine, in addition to aiding in separating the water, decreases the viscosity and makes the filtration easier. Without dilution it is practically impossible to separate the water by gravity. Usually such filtered gum will contain about 3 to 4 per cent water in suspension. This suspended “water” was removed by washing the gum twice with an equal volume of water a t about 95’ C. While the laboratory experiments were concerned primarily with removing dirt from the gum and the production of a clean rosin, it was noted that usually the cleaned gum produced a somewhat higher grade rosin.
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(17) Hall, J. A., IND. ENG.CHEM.,24, 1247 (1932). Hancock* R* s * t s. Patent 1*9089754 (19) Hart, B., Ibid., 947,662 (1910). ( 2 ~ )Hitch, A, R.,Ibid., 1,904,464 (1933). (21) Hitch, A. R., and Ebaugh, I. A., Ibid., 1,899,389 (1933). (22) Hough. H. L., Ibid., 1,092,051 (1914).
The production of clean gum rosin from commercial gum by first cleaning it in the manner described has been successfully accomplished in the laboratory. Although the principles involved in cleaning gum are apparently fairly well understood from laboratory experiments, it is still necessary to conduct the process on a plant scale in order to determine its commercial feasibility. This work is under way a t the Kava1 Stores Station.
u*
tz:;
(25) (26) (27j (28) (29) (30) (31)
Literature Cited Adams, S. B., U. S. Patent 804,911 (1905). Autrey, A. R., Ibid., 1,559,399 (1925). Barraud, M., B d l . l’inst. p i n , No. 41, 1 (1933). Blount, A. C . , U. S. Patent 12,812 (1855). Brooks, J. M., Zbid., 547,202 (1895). Carter, R. O., Zbid., 526,613 (1894). Cashwell, D., Zbid., 70, 956 (1867). Cline, McG., Zbid., 1,945,421 (1934). Col, G., Ibid., 495,543 (1893). Donk, M. G., Ibid., 1,219,413 (1917). Dunwody, R., Zbid., 1,291,800 (1919). Erikson, C. O., Ibid., 984,364 (1911). Fehrman, D., Zbid., 27,624 (1860). Garner, A., Zbid., 251,865 (1882). Gilmer, J. T., Ibid., 709,315 (1902). Gilmer, J. T., Zbid., 961,953 (1910)
$ ~ ~ ~ h ~ ~ ~:i@$b.8$35). ~ ~ ~ ~.~ ~ . $ , ~ L ~A. ~K.,, Ibid., 138,508 (1878). Lee. H. R.. Zbid.. 1.973.172 (19341. McCreary,’J. A., Zbid., 242,015 (1881). Napier, H., Ibid., 31,991 (1861). Palkin, S., and Clark, C. K., IND. ENG.CHEM.,26, 720 (1934). Perlee, R. N., U. S. Patent 961,254 (1910). Peterson, J. M., and Pragoff, E., IND.ENG. CHEM.,24, 173
(1932). (32) Pissimissis, G., and Rigopoulis, J., U. S. Patent 1,219,998 (1917). (33) Sargos, R., Bull. Z’inst. p i n , No. 19, 149 (1931). (34) Schorger, A. W., Naval Stores Rev.,25, 6 (May 8, 1915). (35) Vezes, M., and Dupont, G., “RBaenes et TQrBbenthines,” p. 98, Paris, Librairie J. B. Ballihre et Fils,1924. (36) Ibid., pp. 162-97. (37) Ibid., pp. 170-1. (38) Ibid., p. 174. (39) Winants, J. E., U. S. Patent 72,254 (1867). (40) Winants, J. E., and Griffen, J. F., Ibid., 65,147 (1867). (41) Ibid., 82,263 (1868).
RECEIVED November 11, 1935.
THE METAL WORKERS
Through the courtesy of the Metropolitan Museum of Art, New York, and more particularly of Miss
Nora E. Scott of the Department of Eg ptian Art of the Museum, we are able to o back to about 1440 B.C. in presenting No. 64 in the BerolzXkimer Series of Alchemical and Historical %eproductions. The original painting is in the tomb of Rekh-mi-RE‘, near Thebes. Rekh-mi-RB‘ was Vizier to Thut-
mose I11 and to his son and successor, Amen-hotep 11, of the XVIII Dynasty and served them from about 1470 to 1445 B.C. As chemists we find much that is familiar to us in this picture of metal working in primitive timesthe blow-pipe, the charcoal forge, forceps, hammer-stones, abrasives, polishing, and engraving. 0
A detailed list of the first sixty reproductions, together with full particulars for obtaining photographic copies of the originals, appeared in our issue for January, 1936, page 129, where also will be found Reproduction N o . 61. Reproduction No. 62 appears on page 241 of our February issue, and No. 63 on page 280 of March.
