Botany, Physics, and Entomology in 1 9 3 6
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HEMISTRY is not included in thes^ reviews, as it has been treated in greater detail than is here possible in an
article which appeared on page 4 of the January 1, 1937, issue of INDUSTRIAL AND ENGINEERING CHEMISTRY.
Advances in Botany F . K. I > e m i y , B o y c e T h o m p s o n I n s t i t u t e f o r P l a n t R e s e a r c h , Yonkers, Ν . Υ. Selenium
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ESULTS showing that the selenium absorbed from the soil by plants was the· cause of a serious livestock disease in the north central plains area were reported in the previous review (10). Continuing in this work, Annie M. HurdKarrer (15), United States Department of Agriculture, after having shown that the absorption of selenium by the plant could be retarded by adding sulfur to a toxic seieniferous solution, and after noting the position of this pair in Group VI in tlu» table of elements, sought for a similar behavior in a corresponding pair in other groups, and found it in the arsenic-phosphorus pair in Group V. The toxic action on wheat plants of 30 p. p. in. of sodium arsenate in a nutrient solution was prevented by the presence of 120 p. p. in. of phosphorus. Preliminary results indicate an antagonism between another pair, rubidium and potassium in Group I. The principle involved here is an inhibition of toxicity by the presence of an excess of a chemically similar non toxic element as a simple' mass action, the plant not being able to differentiate between the two elements of the pair liecause of their chemical similarity. Also, Hurd-Karrer and Poos (16) show that wheat plants, although growing without serious injury in a culture solu tion containing 3 p. p. m. or less of sodium selenate, nevertheless contained in their tissues enough selenium to cause the death of aphids and red spider which fed upon the plants. In soils 10 p. p. m. of selenium showed little retarding effect on the growth of wheat, rye, oats, and barley, but aphid infestation was almost completely inhibited. A. L. Martin (21), Columbia* University, also emphasizes the much greater toxicity of selenium to animals than to plants. Buckwheat plants only slightly dwarfed by a seieniferous soil caused early death of rats which ate the tissue, even after dilution with an equal weight of grain. Martin found that moderate rainfall and cropping had little effect in reducing the selenium content of the soil to which selenium had been added. O. A. Beath and C. S. Gilbert (4), Wyoming Agricultural Experiment Sta tion, referring to the leafy carbonaceous shales with high selenium content, suggest that these toxic areas have resulted from the progressive enrichment of selenium in the soils by cycles of the growth and decay during late Cretaceous time of highly seieniferous native plants, espe cially species of Astragalus. Radiation In growing green algae in light of definite wave-length regions, Florence E. Meier (22) found that green light (5000 to 5000 A.) was distinctly injurious to growth, whereas both the shorter and longer wave-length regions corresponding
lue.,
to blue light (4000 to 5200 A.) and yellow light (5500 to 6200 Â.) increased the growth two- to three-fold. Following up a previous observation by Flint, United States Department of Agriculture, that freshly harvested dormant lettuce seed could be induced to germinate if exposed to red light, and that seeds which would otherwise germinate readily could be prevented from germinating bv exposure to blue light, Flint and E. D . McAlister (11), Smithsonian Institution, find that these two regions, one of which stimulates and the other of which inhibits, are precisely at the regions of maximum absorption of light by chlorophyll, and suggest that the cldorophyll content of the lettuce seed is involved somehow in these effects of light. According to R. C. Thompson (SI), Cornell University, the dormancy and light-sensitivity of lettuce seed depends upon the maturity of the lettuce plants at the time the seed is harvested, immature plants producing seed that is dormant and light-sensitive, mature plants furnishing seed that will germinate at once. Also according to N. C. Thornton (33) an exposure of dormant lettuce seed to light is rendered unnecessary if the seeds are first treated with 5 to 20 per cent carbon dioxide in the presence of 20 per cent oxygen. Under these conditions germination in the dark will occur within 17 hours. When agar gels were exposed to ultraviolet radiation (2537 A.) by I. H. Blank and W. Arnold (6), Harvard University, and then were used for the preparation of culture media, the growth of Bacillus subtilis was prevented because of the formation of toxic substances in the agar by the irradiation. This inhibitory effect was produced by irradiating various carbonvdrates used in rpreparing culture media/ Blank and W . N. Tiffney (7) used this principle to obtain bacteria-free cultures of Saprolegnia, the toxic substances produced by irradiating the medium with ultraviolet light inhibiting the growth of bacteria but interfering not at all with the growth of Saprolegnia. J. G. Baumgartner (3), of Crosse and Black well, London, England, found that the toxic substances produced by irradiating agar or sugar solutions with ultraviolet light were acids, approximately one-half of which was formic acid. Neutralizing this acidity restored the capacity of the culture medium to support the growth of bacteria. The unfavorable effect of x-radiation upon the growth of plants according to F. Skoog (27), California Institute of Technology, is caused by the destruction of auxin (natural growth-promoting substance or hormone) and by inhibiting its formation. The inactivation of auxin is accomplished by peroxides or other strong oxidizing agents formed by x-radiation.
Hormones and Growth-Promoting Substances For a number of years it lias been known that the rapid downward movement of the sensitive plant (Mimosa) leaf, which is produced when the stem is touched with a hot rod, cut, or otherwise stimulated, is caused by a chemical substance found in the tissue at the place of stimulation and moving to the leaf base in the transpiration stream of the plant stem. A. Soltys and K. Umrath (28), University of Graz, Austria, have isolated the effective constituent from the sensitive plant tissue and have purified it to such an extent that even in a dilution of 1 part in 100 million the characteristic movement of the leaf is induced. The chemical is thought to be an oxyaeid with high oxygen content and to have a molecular weight of about 500. When the stamens of flowers are removed so as to prevent pollination, the ovary with most plants does not develop further. F. G. Gustafson (14), University of Michigan, applied solutions of indole-acetic, indole-propionic, iiulole-butyric, and phenyl acetic acids to the style of flowers after removal of stamens, and induced further development of the ovary, with the formation in some cases of completely mature fruits without seeds, as with tomato, petunia, salpiglossus, and pepper, or at least with considerable enlargement of the ovary, as with snapdragon, tobacco, squash, cucumber, etc. K. V. Thimann (30), Harvard University, suggests that it is the indole-acetic acid formed by the nodule bacteria which enters the host root and causes the production of nodules on the roots of leguminous plants. Using a purified preparation of "biotin" —i. e., bios l i b (the fraction adsorbed by charcoal), F. Kogl and A. J. Haagen-Smit (18), University of Utrecht, Holland, obtained 63 per cent greater growth of excised pea embryos by adding 0.00008 mg. of biotin per 10 cc. of a culture solution containing only mineral nutrients and sucrose. This represents a dilution of 1 part in 125 million. Biotin, therefore, has a growth-promoting effect not only upon yeast but also upon higher plants. Furthermore, the biotin of various seeds is formed in a definite organ (the cotyledon) and is transported during germination t o the rapidly growing portion of the embryo, a behavior tending to justify the use of the word "hormone" in this connection. Although 2 species of legume nodule bacteria (Rhizobium) would not grow in the absence of natural humic acid, the addition of 1 to 5 p. p. m. caused rapid multiplication. Synthetic humic acids could not replace those from the soil and the iron content was shown not to be a factor (1). D . W. Thome and It. H. Walker (32), Iowa State College, although maintaining that accessory substances are not necessary for the continued growth of these root-nodule organisms, nevertheless agree that increased growth and respiration are obtained by adding them to the culture medium. Agar and extracts of soil, yeast, and alfalfa increased the respiration and in a characteristic manner reduced the respiratory quotient (CO·.» :ϋ 2 ). This is accompanied by a reduction
The AMERICAN CHEMICAL SOCIETY assumes no responsibility for the statements and opinions advanced by contributors to its publications. Published by the American Chemical Society, Publication Office, 20th & Northampton Sts., Easton, Pa. Entered as second-class matter at the Post· Office at Easton, Pa , under the Act of March 3, 1879. as 48 times a year. Industrial Edition monthly on the first; Analytical Edition monthly on the 15th; News Edition on the 10th and 20th. Acceptance for mailing at special rate of postage provided for in section 1103. Act of October 3, 1917, SUBSCRIPTION to non-members, INDUSTRIAL AND ENGINEERING CHEMISTRY, $7.50 per year. Foreign postage $2.10. except to countries accepting mail at American domestic rates; Canada, 70 cents. Analytical Edition alone, $2.00 per year; foreign postage, 30 cents; Canada. 10 cents. News Edition alone, $1 50 per year (single copies. 10 cents); foreign postage. 60 cents: Canada, 20 cents. Subscriptions, changes of address, and claims for lost copies should be sent to Charles L, Parsons. Secretary, 728 Mills Building. Washington, D. C.
J A N U A R Y 10, 1937 in the value of the oxidation-reduction potential of the medium. They believe that one of the important functions of the accessory substances is to provide readily available hydrogen donators as a source of energy. In experiments by W. J. Robbins, V. B. White, J. E. McClary, and M. Bartley (#5), University of Missouri, excised root tips which have a limited growth in a synthetic culture solution will show a five- or six-fold increase if a small amount of agar, or even a piece of filterpaper, is added to the culture solution. The effect is due not to organic materials but t o elements in the ash, since the crude ash of the agar or filter paper produces the same result. Similarly, in the experiments of R. A. Steinberg (29), United States De partment of Agriculture, the decrease in the growth of Aspergillus nicer by puri fication of the sucrose by alcohol extrac tion is interpreted not to come about because of the progressive removal from the sucrose of a "bios" substance or "coenzyme R," but because of the re moval of zinc and molybdenum. When yeast decoctions or malt extracts are added to the culture medium as a source of or ganic accessory substances for A. niger, his view is that the increased growth may be due to the heavy metals added simul taneously. Molybdenum was found to be essential for the growth and develop ment of this fungus. Germination-Inhibiting Substance Previously A. L. Shuck (26), New York Agricultural Experiment Station, Geneva, had found that successive sowings of lettuce seed upon the same piece of moist cotton results in a progressive decrease in germination owing to the accumulation of a germination-inhibiting substance which diffuses from the seed into the cotton. A further development in this field has been reported by H. Borriss (8), University of Greifswald, Germany. Seeds of Vaccaria pyramidala will not germinate on blotting paper but will do so if sown on soil, charcoal, collodion, or aluminum hydroxide. This is because these media absorb a germination-inhibiting substance from the seeds. Germination occurs on blotting paper if a current of water is allowed to now slowly through the paper and thus carry away the inhibitor. Since a layer of soil is effective in absorbing the inhibitor, even if the soil and seeds are separated by an air space of 3 cm., it is believed that the inhibiting substance is volatile. P l a n t Color Preservation A simple method of preserving speci mens of nowers so that the color will be re tained has been developed by W. D . Pierce (23), office of Biological Abstracts. The flower is pressed down upon plain cardboard and is covered with overlapping strips of Scotch cellulose tape, pressing smoothly and tightly. The plant parts are dried by placing between blotting papers. Entomological specimens may be mounted in the same way, as may also plant patho logical samples in which retention of color is important. Plant parts used in the original tests had held their color for 10 to 11 months at the time of the report. Virus Disease a n d Fluorescence Tobacco leaves infected with certain virus diseases develop lesions which take the form of spots. When such tobacco plants were taken to a dark room and ex amined by ultraviolet light, R. J. Best (6), University of Adelaide, Australia, noted that the spots were surrounded at their edges by bright bluish fluorescent rings or haloes. This fluorescence is caused by a water-soluble organic substance which is
NEWS EDITION
e
resent in small amounts in healthy plants ut t o a much greater extent in virusinfected plants. When a leaf which was spotted with disease-lesions was pressed between sheets of white blotting paper the leaf lost its fluorescence but the blotter, which in daylight looked like a clean, unused piece of blotting paper, when viewed under ultraviolet light showed a bright fluorescent outline of the leaf, and when photographed under this condition gave an excellent photograph of a leaf. Wounding and Respiration Rate
Various previous investigations have shown that an increase in respiration may be expected to follow a treatment whicn causes a wounding of the tissue. L. J. Audue (2), Cambridge University, England, shows how slight this "wounding" needs to be to produce an effect. Rubbing the leaves on both sides by a finger covered with a finger stall, or merely bending the leaf either by hand or by a mechanical arrangement increased the respiration two- to three-fold. The respiration then decreased but the effect held for as much as 60 hours after the "treatment." And H. Godwin (12), also at Cambridge, finds that the handling of leaves, such as is re quired in transferring leaves from one experimental chamber to another, "hold ing the leaves between finger and thumb, singly or together, and bending and rub bing them lightly past one another," results in a large increase in the respiration of the leaves. N i t r o g e n Trichloride a s a Fungicide This gas which is used in the treatment of freshly milled flour has been found to be effective in preventing decay in citrus fruit and is now in use commercially for that urpose. See a report by L. J. Klotz (17), Tniversity of California, regarding co operative tests with A. E . Nelson of the California Fruit Growers Exchange, and J. C. Baker and T. E . Galvin of the Wal lace and Tiernan Products Co. Thus, oranges may be gassed soon after picking, again after packing, and a third time after the fruit is loaded in the car. The gas kills the spores on the surface of the fruit but does not destroy the mycelium after it has once penetrated into the inner portions. It will penetrate the wrappers of a packed box of fruit. Apparatus for the safe pro duction of the gas in dilute concentrations in air, and for its application within stor age rooms and refrigerator cars has been developed. Monomethylchloramine may be substituted for nitrogen trichloride but at greater cost.
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Vernalization or Iarovization By this method, proposed in 1932 in Russia by Lysenko, seeds are brought to an early stage in germination and then stored at low temperatures, within the range 0° t o 5° C , for the proper period, approximately 35 to 45 days, suitable tem perature and storage periods varying with different plants. The treatment shortens the time reauired for passing from the vege tative to the reproductive phase. Thus, winter wheat need not be planted in the fall and be subjected to the danger of winter killing in a severe climate. It may be ' 'iaro vized and planted in the spring, producing a crop in early summer ana thus behaving as though a winter wheat had been con verted into a spring wheat. R. McKee (20) reports results of vernalization tests with various seeds, such as white lupine, crimson clover, hairy vetch, and Austrian winter field pea. The vernalization treat ment induced flowering and fruiting of these plants, whereas the seeds not treated either produced plants which remained en tirely in the vegetative stage or bloomed at
3 a later date. At one time it was suggested that the effect of this treatment was upon the enzyme system in the food reserves stored external t o the embryo, but F. G. Gregory and Ο. Ν. Purvis (18), Imperial College of Science and Technology, London, England, obtained the effect when the ex cised embryos were separated from the seeds and vernalized apart from contact with the endosperm. A quite different re sult was obtained, however, with tomatoes and cucumbers by S. Burr and D. M. Turner (9), University of Leeds, England. Vernalization of these seeds definitely re tarded fruit setting and ripening. Wasting D i s e a s e of Eel-Grass The epidemic disease which has almost entirely destroyed extensive areas of aquatic plants on the Atlantic coast of both Europe and North America by killing the eel-grass, which is an important food plant for migratory game birds and which re tards the erosion of bottoms of bays and estuaries, appears to be due to parasitism by a species of Labyrinihula, "an amoeba like organism with mycetozoan affinities," according to extensive observations and accurate experimentation by C. E. Renn (24), Woods Hole Océanographie Institution and New Jersey Agricultural Experiment Station. Filterable O r g a n i s m s A new group of organisms obtained from sewage, passing through porous filters with a pore diameter larger than 0.25 μ and which can be cultured in artificial media indefinitely, has been discovered by P. P. Laidlaw and W. J. Elford (Î9), National Institute of Medical Research, Hampstead, England. These organisms are thought possibly to be a connecting link between bacteria and the viruses. Literature Cited (1) Allison, F . E . , a n d Hoover, S. R., Soil Sci., 4 1 , 3 3 3 (1936). (2) A u d u s , L. J . . New Phytologist, 34, 386 (1936). (3) B a u m g a r t n e r , J. G., J. Bad., 32, 7 6 (1936). (4) B e a t h , Ο. Α., a n d G i l b e r t , C. S. t Science, 8 4 , 484 (1936). (5) Beet, R. J., Australian J. Expt. Biol. Med. Sci.. 14, 199 (1936). (6) B l a n k , I. H . , and Arnold, W . , J. Bad., 30, 507 (1935). (7) B l a n k , I . H . , a n d Tiffney, W . N . , Mycologia, 2 8 , 324 (1936). (8) Borriss, H., Ber. dent. bot. Gesell., 54» 472 (1936). (9) B u r r , S.. a n d T u r n e r , D . M . , Gard. Chron., 9 8 , 288 (1935). (10)
(11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23)
Denny, F. E.,
I N D . E N G . CHEM., N E W S
E D . , 13, 4 7 4 ( D e c . 2 0 , 1935). Flint, L. H . , a n d McAlister, E . D.„ Science Suppl, 8 4 . N o . 2171, 8 (1936). G o d w i n , H . , New Phytologist, 34. 4 0 3 (1936). Gregory, F . G., and Purvie, Ο. Ν . . Nature, 138, 2 4 9 (1936). Guetafson, F . G., Proc. Nat. Acad. Sci., U. S., 22, 628 (1936). H u r d - K a r r e r , A. M., J. Wash. Acad. Set., 26, 180 (1936). H u r d - K a r r e r , A. M . , a n d Poos, F . W . , Science, 8 4 , 252 (1936). K l o t z , L. J., HUgardia, 10, 27 (1936). Kôgl, F . , a n d H a a g e n - S m i t , A. J., Z. physiol. Chem., 243. 209 (1936). Laidlaw, P . P.. a n d Elford, W . J., Proc. Roy. Soc. (London), B120, 292 (1936). McKee, R., U. S. Dept. Agr. Circ. 377 (1935). M a r t i n , A. L . , Am. J. Botany, 23, 471 (1936). Meier, F. E . , Smithsonian Inst. Misc. Collections, 94, 1 (1936). Pierce, W . D . , Science, 84, 2 5 3 (1936).
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INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
(24) Renn, C . E.. Biol. Bull, 70. 148 (1936). (2δ) Bobbins. W. J., White, V. B., McClary, J. E . , and Bartley, M-, Proc. Nat. Acad. Set.. U. S.t 22, 636 (1936). (26) Shuck, A . L. f Proc. Intern. Seed Test Assoc., 7, 9 (1935). (27) Skoog, F., J. Cellular Camp. Physiol., 7, 227 (1936). (28) Soltys, Α., and Umrath, K.. Biochem. Z., 284, 247 (1936).
(29) Steinberg, R. Α., / . Agr. Res., 5 2 , 4 3 9 (1936). (30) Thimann, K. V.. Proc. Nat. Acad. Set., U. £ . , 22, 511 (1936). (31) Thompson, R. C , Proc. Am. Soc. Hort. Set., 33, 610 (1935). (32) Thorne, D. W., and Walker. R. H . , Sou Set., 42, 301 (1936). (33) Thornton, N . C , Boyce Thompson Inst. Contrib. 8, 25 (1936).
Some Developments in Economic Entomology
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OLLOWING along in the work with surgical maggot secretions including allantoin as stimulants to the healing of wounds, William Robinson in coopera tion with many physicians found that 2 per cent aqueous solutions of urea would stimulate healing in chronic purulent wounds. The effects obtained are a cleansing of the wound by removal of necrotic material and pyogenic bacteria present and a promotion of the growth of granulation tissue. Urea, like allantoin, occurs in surgical maggot secretions and its presence serves as a further elucidation of the remarkable efficiency of surgical maggots in healing chronic suppurating wounds. In use, the 2 per cent urea solution is applied directly to the wound on saturated gauze dressings. The heal ing action of urea probably accounts in part for the custom prevalent for cen turies in Europe, Asia, and Africa and also practiced in America of using urine to promote cleansing and healing of wounds. Pyrethrum-—Derris a n d C u b e The toxic action of pyrethrum powder on cockroaches is one mainly of absorp tion of this insect poison through the outside body covering (integument). Hockenyos concludes that there is httle effect of penetration of the poison through the breathing system (spiracles) or by ingestion through the mouth. LePelley and Sullivan have shown that alcoholic solutions of rotenone are 5 to 6 times as effective against houseflies as solutions of the pyrethrins. These two potent insect poisons work well together but there was no striking synergistic effect noted. The physical condition of the pyrethrins at the time of application on the insects is a determining factor according to Hartzeil and Wilcoxon in the relative toxicity of pyrethrins I and II. Acetone extracts nieh in pyrethrin I content were consider ably more toxic in aqueous sprays on aphids than extracts high in pyrethrin II content. Using a miscible oil as a solvent, however, these differences tended to dis appear. The effectiveness of kerosene solutions high in pyrethrin I or pyrethrin II content were not significantly different in tests on flies. Acree, Schaffer, and Haller show that pyrethrins I and II are present as such in fresh pyrethrum flowers and that the method of drying the flowers produced little variation in the pyrethrin content. Allen has shown that mist sprays of kerosene steepates of pyrethrins were promising for potato leafhopper control. A hood is used in confining trie spray to the plant. Kerosene steepates of derris showed promise on the potato flea beetle. Derris and cube dusts at equal rotenone content were shown by Chamberlain to be about equal in toxicity to the tobacco flea beetle. Dudley, Bronson, and Car roll showed that a derris powder spray (0.0044 per cent rotenone) was effective for pea aphid control. A residual toxic action against the aphids was noted to be present over a period of 1 to 2 weeks or more after spraying. Derris powder sprays were found by Heal to be effective in control of the red mite on apple trees.
Jones and Smith conclude that an ap proximate chemical value of the potency of derris and cube roots t o house&es can be calculated from the rotenone and total extractive contents. For derris roots the figure is rotenone content plus 0.5 (total extractive content minus rotenone). This applies to benzene and carbon tetra chloride extracts. For acetone extract a 0.4 factor in place of 0.5 is used. For cube root the toxic value is similar but the factor 0.4 is used for extractives of all 3 solvents. Ovicides A 1 to 2 per cent oil emulsion containing 1 t o 2 per cent dinitro-o-cyclohexyl phenol in the oil base has been shown b y J. F. Kagy and C. H. Richardson t o have very decided egg-killing properties in tests against the San Jose scale and the eggs of a plant bug Lygus. The indications were romising for the use of dinitro-o-cycloexyl phenol (DNOCHP) in dormant sprays. Dutton also showed the high toxicity of DNOCHP in petroleum oil emulsions as dormant sprays against the eggs of the rosy apple aphid and black cherry aphid. Promising results for citrus mite control were obtained with D N O C H P sprays by Boyce and Frendergast. Breakey and Miller showed that emulsions of oil solutions of chlorinated naphthalene possessed considerable ovicidal action on codling moth and oriental fruit moth eggs. Vegetable oils, such as cottonseed, corn, and soybean oils, were found by Hough and Jefferson to have a n ovicidal action comparable to petroleum oils on codling moth eggs.
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Fumigants In fundamental studies on fumigating action, William Moore concludes that the concentration of hydrocyanic acid gas is of double the value of the length of ex posure in effecting a kill against the re sistant6 red scale of California. Κ = C(T)· . In other words, a short exposure with a high concentration was more effec tive than a long exposure at low concen tration. On the other hand, the concen tration of fumigant t o which the nonresistant red scale is exposed is approxi mately of equal value8 t o the length of exposure Κ = C(T)· . Increasing the temperature slightly increases the kill of non-resistant red scale but, surprisingly, lowers the kill of the resistant red scale. Liquid hydrocyanic acid was found to be the most effective of various cyanides by Cotton, Young, and Wagner for use in flour mills. By piping the fumigant directly to the milling machinery and spraying it under pressure, fumigation can be carried out more efficiently and at a lower cost. Coleman states that tetrahydronaphthalene was more effective against the webbing clothes moth than ethylene dichloride. Relation o f Optical A c t i v i t y of O r g a n i c C o m p o u n d s o n Toxicity Starr and C. H. Richardson found that levo-a-p-tolylpyrrolidine was much more toxic to aphids than the dextro form,
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though at the median lethal point the two are close together. Craig and Rich ardson have shown that a cW-nicotine is only one-half as toxic as 2-nicotine t o aphids. Fink and Haller in tests on mosquito larvae found optically active dihydrodegnelin and isorotenone more toxic than the corresponding optically inactive forms. W e t t i n g a n d Spreading A g e n t s Certain sulfonated and other com pounds continue to show promise as sub stitutes for soap in insecticidal sprays. Heal, Schmitt, and Ginsburg found the sodium salts of sulfonated diphenyl com pounds to be promising for use with sulfur, petroleum oil emulsions, and derris powder. Because of their compatibility with hard water and tolerance by plant foliage they show promise in replacing soap. Blood albumen is another spreader which has come into use in recent years, especially in combination with petroleum oil emulsions. R. H. Smith and J. P. LaDue report on further studies with it.
Progress in Physics in 1936 Henry A. B a r t o n , Director, A m e r i c a n I n s t i t u t e of P h y s i c s , 175 F i f t h Ave., New York, Ν . Υ. HE year 1936 in physics has been one of good average vigorous progress in fundamental xesearch. Excellent though this is, we have become in recent years so spoiled by brilliant advances and epochmaking discoveries that it is easy to forget we are still in the midst of what Dr. Darrow describes as the "Renaissance of Physics." The discovery of neutrons, deuterons, and positrons has opened up fields amounting in magnitude to whole branches of science. The influence of these discoveries has gone far beyond the borders of physics through the allied fields of chemistry and biology and into medi cine. It cannot yet be said that these three elemental particles have achieved appreciable industrial importance but very likely that will come.
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N u c l e a r Research Physicists investigating the neutron have found its lack of electric charge both a help and a hindrance. It is a help that the neutral neutron can readily slip through the repulsive electric fields guard ing atomic nuclei and, once inside the wall, cause all kinds of alchemical and radio active fireworks which are most revealing about both missile and target. It is a hindrance that man-made electric fields are unable to influence the neutrons in their flight, because it is with the use of such fields that the speeds, masses, and other properties of charged particles are determined and controlled in the labora tory. Physicists have found that the neutrons can be slowed down by collisions with other small atoms so as almost to reach thermal equilibrium at ordinary temperatures. Such slow neutrons are readily intercepted and absorbed by atomic nuclei. Ordinary hydrogen atoms are converted to deuterium atoms by this process. A beginning has been made in the measurement of neutron absorption coefficients of various materials. These vary widely from one element to another and as a function of neutron velocity. There seem to exist "resonance" effects or critical speeds which are just right for absorption. As for what happens to nuclei when they absorb neutrons, or when they are struck (Continued on page 15)
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J A N U A R Y 10, 1937 of each in turn be made available to all the rest. At the conference the following phases of laboratory operation were discussed: laboratory procedure and forms; supplies and equipment; laboratory funds; meth ods of analysis; exchange of samples be tween laboratories; methods of sampling; and other equally pertinent problems. In the course of their conference in Washington the chief chemists visited the headquarters laboratory of the Bureau of Internal Revenue, the National Bureau of Standards, and the laboratories of the Department of Agriculture. After their Washington conference, they visited the Philadelphia laboratory of the Bureau of Customs, which is the most recently reno vated laboratory in the Customs Service. This was followed by an inspection of the New York laboratory. P h y s i c s a n d C h e m i s t r y of M e t a l s to Be Discussed at Μ . Ι. Τ. HE rewards of cooperation in research in t h e field of metals through joint invesT gation of fundamental problems by physi cists, metallurgists, and chemists will be discussed by leaders in these fields a t a meeting t o be held a t the Massachusetts Institute of Technology on January 28 a n d 29 under the auspices of the institute a n d the American Institute of Physics. T h e meeting emphasizes the promising trend toward a most productive type of research in which technical workers bring to prob lems of fundamental interest the special ized knowledge and methods of their several fields. T h e purpose of the meeting is to discuss thoroughly recent developments in t h e physics and chemistry of metals, as well as the opportunities for still greater advances through the combined cooperative efifort of all workers whose knowledge may in some way contribute to problems of m u tual interest. From a half to one hour each will be allowed for presentation of t h e important papers and ample time will be given for discussion. Some of the more general papers to be presented are: "Research Problems in t h e Steel Industry," by E. C. Bain, United States Steel Corp.; "Inclusions in Ferrous Alloys," b y A. B. Kinzel, Union Carbide and Carbon Co.; "Flow Phenomena in Heavily Stressed Metals," by P. W. Bridgman, of Harvard; "Electronic Structures in Metals and Alloys," by J. C. Slater, head of the Department of Physics at M. I. T . : "Corrosion," by J. R. Bums, of the Bell Laboratories; "Elastic Properties of Ferrous Alloys," by A. V. de Forest, of M. I. T . ; and "Chromium-Nickel-Iron Alloys," discussed by V. N. Krivobok, of the Allegheny Steel Co. In another group of papers various tech nics and their applicability are to be pre sented, while in the third group some especially complex scientific problems met with in ferrous alloys will be discussed. Arrangements for the meeting are in charge of John Wulff, of the Massachusetts Institute of Technology, Cambridge, Mass., who will act as secretary, and Henry A. Barton, director of the American Insti tute of Physics.
Broadcasts of Northeastern Section HE Northeastern Section announces T the following broadcasts by members of the section: January 8
M. J. Ahern, Weston College, "Chemistry of 1936. I." January 15 M. J. Ahern, "Chemistry of 1936. I I . " January 22 Ernest H. Huntress, Massa chusetts Institute of Tech nology, "Nature's Paint Box—the Coloring Matters of Fruits and Flowers." January 29 John A. Seaverns, Chairman, Broadcast Committee, "The Chemistry of the Automo bile—Tires and Ignition." Copies of the talks may be obtained a t 7 cents each from John A. Seaverns, 99 Broad St., Boston, Mass.
Progress in Physics (Continued from page 4) by fast atomic particles, physicists have learned a great deal. Each target element investigated presents its own character istic behavior as to (1) the kinds of trans mutations it may undergo, (2) the rela tive likelihood of each as a function of the energy of the striking particle. The products formed have their own charac teristics, such as stability or instability and, if the latter, average time of life and character of radiations emitted. The number of known alchemical reactions has already gone into the hundreds. Nuclei are found to have "excited states" and to emit "line" spectra. These states or energy levels are measured in hundreds and even thousands of kilovolts and the radiations are in t h e gamma-ray region or beyond. The energy of constitution or excitation of nuclear particles contributes, according to the Einstein law, to their mass. This law has been verified experimentally and great progress has been made in deter mining atomic weights more accurately t h a n ever before. These weights have been deduced from observed energetics of nuclear reactions a n d then confirmed in general by improved mass-spectrum meas urements b y Aston, Bainbridge, and Dempster. An extremely important outcome of nuclear research is tne fact that unstable or radioactive isotopes have been pro duced in the case of many common ele ments—e. g., sodium and phosphorus. These may be enormously useful to chem ists and biologists as "tracers," whereby the atoms of these elements may be fol lowed through complicated reactions and biological processes. I t is t h e old method of tagging fish and birds applied to funda mental chemistry. These materials are being produced mainly by the use of cyclo trons, a number of which have been p u t into operation in various parts of the country. Other devices, directly em ploying high voltages, are also available. Physicists, concerning themselves with the fundamental properties of the ultimate elements of matter, are greatly interested in the law of force between such particles as protons, neutrons, and electrons. Tuve and others have successfully studied the scattering of protons by protons and several experimenters are studying the similar interaction between protons and neutrons. The forces thus studied are those which account for the stable con stitution of matter. Present results indi
15 cate that protons and neutrons all have the same, close range, attractive forcefields. Superposed on these are t h e repul sive Coulomb fields d u e to t h e electric charge in the case of protons. There are also fields due to t h e spin of t h e particles. I t is now clear t h a t cosmic rays should be classified under nuclear research, not t h a t we have knowledge of their origin b u t rather because cloud-chamber and counter experiments show t h a t they interact freely and violently with atomic nuclei. It was in the course of such experiments that Carl D . Anderson m a d e the discovery of the positron in 1932, for which he was this year awarded t h e Nobel Prize. Sharing the prize with him is Victor Hess, original discoverer of the cosmic rays themselves. Partly by the nature of nuclear reactions produced by cosmic rays, but more b y studies of how the rays vary in intensity over the face of the e a r t h because the earth's magnetic field affects moving charged particles, Compton and others conclude that practically all primary rays are such particles. Most observers agree with him, but Millikan a n d his colleagues still hold that a t least a large part of t h e rays are photons. All will agree t h a t they may have enormous energies per "ray, running up to billions of electron volts. Secondary rays, which are the positrons, electrons, photons, and probably others coming from primary-ray-tœ.-nucleus encounters, are being intensively studied. They may appear singly, in pairs, in showers, or even in bursts of many rays. These phenomena, once interpreted, will obviously tell much a b o u t both the primary rays and the nuclei. X-Rays I n the field of x-rays, measurements have been carried to greater extremes of accuracy, resolution, a n d wave length. Measurements of absorption coefficients of the elements have been made in t h e wave-length region between ordinary x-rays and gamma-rays. X-rays have been extensively used t o study the state of electrons in metals a n d to throw light on the behavior of a t o m s in solids as a function of temperature and chemical association. For several years physicists have been puzzled by a discrepancy between the value of tne electronic charge, e, derived from x-ray and density measurements of crystals on the one hand and the famous Millikan oil-drop experiment on the other. The discrepancy, it seemed, was larger than the possible error of either method. This year the difficulty h a s been traced to the figure used by Millikan for the viscosity of air in the relationship deriving drop sizes from rates of fall. The latest value of e is 4.799 * 0.007 X 10" 1 0 e. s. u. Low-Temperature Research Mention should be m a d e of advances in low-temperature research. Interest centers once more on t h e phenomenon of super-conductivity. A combined experimental and theoretical attack on this mystery is undoubtedly making headway but it is too early to forecast conclusions. Professional A d v a n c e s In this review of fundamental research progress, no mention could be made of professional advances. Physicists are trying to introduce their services and those of their science to industries and t h e general public. Announcement has recently been made t h a t a new monthly Journal of Applied Physics will make its first appearance in J a n u a r y , 1937.
