Continuously Evacuated Demountable Vacuum Equipment The Use of Special Oil Distillâtes G· H. S* Tupholme, Runcton Cottage, Lower Bourne, Faraham, Surrey, England EGINNING with the discovery by C. R. Burch in the research laboratories of B the Metropolitan-Vickers Electrical Co.
of a series of oil distillates (now known as the "Apiezon" series) having exceptionally low vapor pressures, a vacuum technic has been developed that has led to a remarkably rapid advance in all branches of science and engineering requiring the production and maintenance of very high vacua. The discovery of Apiezon oils has made possible the complete elimination of liquid air and similar cold traps from high-vacuum pumping equipment, thereby removing such equipment from the category of purely laboratory type apparatus and increasing its usefulness to the engineer. Apiezon distillates are now commercially available as a series of low-vapor-pressure products in the form of grease compound and wax, of extreme value for the sealing of vacuum apparatus. Some of the important possibilities opened up by these advances have already been realized by the production of a range of high-vacuum demountable equipment continuously evacuated by means of Apiezon oil condensation pumps, and sealed with the aid of Apiezon products. This equipment has been designed throughout on engineering lines. Glass, rubber, and similar laboratory materials have been practically eliminated and an exceedingly robust construction achieved, utilizing metal and porcelain instead. The feature of demountability is of considerable importance. Until recently, x-ray tubes, wireless transmitting valves, and similar apparatus have, of necessity, been made of glass, and have been further restricted in their development by the fact that they were permanently sealed, so that any failure necessitated complete replacement or very expensive repair. In contrast with this, the new equipment is so designed that, for the purpose of adjustment and repair, or internal alterations required in the course of scientific research, it can easily be taken to pieces and reassembled with ordinary engineering tools, and again placedin operation within the space of a fewhours. The development and manufacture of a 500-kilowatt demountable continuously evacuated transmitting valve for use at the G. P. O. Rugby Wireless Station is some indication of the commercial possibilities arising from the applica-
PRODUCT
APPLICATION
the tube being such as to permit quite straightforward assembly. This is fur ther facilitated by the complete interchangeability of the various anticathodes used for different types of radiation. Power is obtained from a transformer having a peak voltage of 100 kilovolts at 70 milliamperes. This voltage can be regulated in small steps between zero and the maximum by means of a n autotransformer. The filament transformer is con tained in the main transformer tank, the filament emission being controlled by a rheostat in the primary circuit. The power dissipation in the target de pends, of course, on the size of the focal spot, and the focus of the x-ray tube can be easily adjusted to meet special require ments. For powder work, inputs of 1 kilowatt—i. e., 40 milliamperes at 50,000 volts (peak)—can be used with a copper target, and under these conditions sharp, properly exposed photographs of a copper wire can be taken on a 9-cm. camera with an exposure as short a s 5 minutes. Single crystal reflections can be seen on a fluorescent screen, which considerably facilitates the determination of crystallograpbic axes. The cathode ray oscillograph has been developed specially for the recording of ultrarapid transients, such as those set up by lightning, insulator discharges, and switching operations on high-tension trans mission unes. Transients of this nature may occupy periods as short as 0.5 to 1 microsecond, while records of phenomena lasting from 10 to 100 microseconds are commonly required. Such extremely high speeds of recording necessitate a cath ode ray beam with a photo or visual intensity that can be realized only by the use of a high-voltage tube. This should not be confused with the medium-voltage continuously pumped tube, nor with the small permanently sealed glass type. Both of these, while extremely useful for recording periodic phenomena, are of no use for the investigations of the single swift transients encountered in highvoltage engineering. The latest cathode ray oscillograph has the following features : It is a high-voltage tube with a cathode ray beam of such intensity that transients of duration as short as one-fiftieth microsecond can be clearly and accurately recorded.
RANGE OF APIEZON PRODUCTS Now ON THE MARKET VAPOB Passeras SAFB TBMPBRATUBS TO AT ROOM TBMPBRATUBB MAXIMUM WHICH SBALINO ΑΓΓΚΒ EVOLUTION TEMPERATURE MBDIA SHOULD BB * or DISSOLVBD AIR IN Ues RAISED TO APPLY
Condensation pumps Condensation pumps " For oil-lubricated tape and places wbere a moderately viscous oil of low vapor pressure is required For placée wbere an exceedApieson oil Κ ingly viscous oil of very low vapor pressure is required Ground, well-fitting joints. Apieson grease L Temporary work. Glass conical taps For places where a grease of Apieson grease M moderately low vapor pressure is required Apieson sealing Unground joints compound Q Apieson wax W Permanent joints • 1 micron — 10 ·'» mm. mercury. Apieson oil A A pies on oil Β Apieson oil J
tion of the new vacuum technic. The same technic, by providing greatly improved methods of approaching a difficult problem, played a vitally important part in the brilliant experiments by Dr. Cockcroft and Dr. Walton at the Cavendish laboratory, which resulted in the splitting of the atom. Various types of commercial plants have just been placed on the market in which these new old distillates are part of the essential equipment. This includes xray equipment for crystallographic analysis, cathode-ray oscillograph for ultrarapid recording, and a resistance-type vacuum furnace. The x-ray equipment for crystallographic analysis has already been found of great value for the determination of the composition of materials, the arrangement of the constituent elements of various compounds, the phase changes in metallic alloys, and similar investigations. It is an excellent example of the new continuously evacuated apparatus, embodying as it does the features of practically all-metal construction and demountability. The complete equipment comprises two units: (a) the x-ray apparatus, including the tube, evacuating pumps, and H. T. and filament transformers (arranged in one tank), all of which are compactly mounted together on a steel framework occupying afloorspace approximately β Χ 4 feet; (o) the control equipment, which is mounted separately and includes the regulating gear, switches, instruments, protective relays, and indicating lamps. The x-ray tube is of the hot cathode type, entirely demountable and, with the exception of the porcelain insulator, of all-metal construction. The metal head carries two thin aluminum windows, and since the beam is taken from the anticathode at a glancing incidence, two cameras may be used at the same time. The tube is very stable in operation be cause of the pumping arrangements which deal effectively with any evolution of gas, evacuation being by means of an oil con densation pump in series with a rotary backing pump. All the ground jointe are sealed with Apiezon low-vapor-pressure products. The feature of demountability makes the renewal of the filament or the changing of the target a simple matter, the design of
PACKING
0.01 micron0 at room ternperature 0.0001 micron at room ternperature 1 micron at 250° C.
.... .... ....
1 micron at 300° C, immeasurably low at room temperature 1 micron at 300° C, immeasurably low at room temperature 1 micron at 200° C.
.... 30° C.
Room temperature
Jar of approx. 1 us.
30° C.
Room temperature
Jar of approx. 4 os.
1 micron at room tempera· ture 1 micron at 180° C
30° C 80° C.
Room temperature 100° C
Tin of approx. 1.5 lb.
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Bottle of approx. 16 oe. Bottle of appro*. 16 os. of approx. 4 oe. { Bottle Bottle of approx. 16 os. Jar of approx. 1 os.
In Mb. sticks
FEBRUARY 20,1937 It is completely demountable for purposes of internal alteration or adjustment. The use of Apieson oil distillates in the pumping equipment and for sealing purposes has, among other advantages, that of eliminating the eventual deterioration of brass parts which occurs when mercury pumps are used without special cooling agents. The construction is such that the photographic film is placed inside the vacuum where it is directly impinged on by the beam. The photographic intensity thereby obtained is so great that phenomena are clearly recorded, even when the instrument has been very carelessly adjusted. The recording of a transient is initiated automatically by the transient itself, which makes the oscillograph suitable for recording unexpected impulses, such as those caused by lightning, etc. This is superior to any system in which the operation of the oscillograph is dependent upon the generation of an impulse by artificial means at a predetermined moment. Furthermore, by the use of a suitable delay circuit the time-sweep plates of the cathode ray tube are excited a fraction of a microsecond before the voltage fluctuating plates. Consequently, the whole of the impulse is recorded, whereas with the more common simultaneous excitation of both pairs of plates the beginning of the record is lost.
A Ten-Year View of Chemical Foreign Trade WORLD trade in chemicals and allied products showed a decided upward trend in 1936. with the United States recording the largest gains of the major chemical manufacturing and trading countries, according t o official trade statistics for the first 9 months of 1936, in comparison with those for a similar period of 1935. If comparisons are made with similar data 10 years ago, and if shipments for t h e last quarter o f 1936 continued at the same rate as for the first 3 quarters, the same relative positions of the 3 major countries were held as at that time; Germany, however, probably will show a small increase in its exports; the United Kingdom may equal its 1926 figure; but the United States may register a decline. These statements are made from analyses of statistics based on dollars. France was the next largest exporter. Japan will record a substantial advance over 1926 even though its currency is valued considerably lower than a decade ago. The world-wide trend towards greater self-sufficiency for many products, especially those designed t o relieve national dependency upon foreign countries in times of emergencies, continued in 1936 with redoubled force. Many new plants were reported under construction m the central and eastern European countries and the Italian government issued permits for erection of a number of plants. In the Far East, Japan was reported to be continuing its rapid development of an imposing chemical industry by expanding older plants and building many new ones. China and British India also have several new chemical plants already planned or under construction. In South America comparatively few plants have been reported so far this year and in Central America less than 10. Compared with 10 years ago, the number of plants manufacturing or assembling chemicals and allied products has increased greatly in all parts of the world. Raw materials and industrial chemicals generally show very marked gains, while finished products, such as perfumery, toilet preparations, and some paint products, record some· what lessened foreign trade.
NEWS E D I T I O N
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The United States held first place increase was recorded in 1936 to a total among the chemical importing countries of $23,000,000; imports into Japan, howof the world, with imports exceeding ever, were up 30 per cent t o $41,000,000, $96,000,000 during the January t o Sepnotwithstanding almost complete distember, 1936, period, 21 per cent greater appearance of some commodities formerly than in the corresponding period of 1935, imported in large amounts. Japan not and second place among exporters with only extended its markets i n the Far East exports of more than $113.000,000. which and Africa, but gained ground in the were 19 per cent greater than in January Western Hemisphere. Conspicuous int o September, 1935. For the most part creases were made in exports of médicinale, the import trade of the United States is toiletries of all kinds, and industrial chemisimilar t o that of 10 years ago when, for cals, such as sulfur, calcium carbide, example, sodium nitrate ranked first, and bleaching powder, ammonium sulfate, and in 1936, second in importance. Tung calcium carbonate, while reductions ocoil, the fifth largest chemical item in curred in menthol, camphor, and matches. value imported in 1926, held first place in 1936; creosote oil, the second highest in value, has fallen to sixth place; and H. W. SWANK, who has completed the shellac, in fourth place, has dropped to a requirements for the degree of doctor relatively minor position. In the export of philosophy in chemistry at Purdue trade, rosin and turpentine hold important University, has accepted a position with places in both years. Sulfur, caustic soda, E. I. du Pont de Nemours & Co., Inc., benzene and coal-tar dyes, phosphate rock, Buffalo, Ν. Υ . disinfectants and insecticides, paint products, and médicinale have remained in about the same relative positions; carbon Bausch & Lomb's N e w Labora black, coal tar and coal-tar pitch, borax, tory for Applied Research and synthetic plastics have assumed much more prominence, and perfumery and AUSCH & LOMB has opened a new labo toilet preparations, ammonium sulfate, ratory for applied research in order ginseng, zinc oxide, dynamite, and superto enter upon a broad program of funda phosphates have dropped to relatively mental investigations on the chemistry unimportant places. There has been and physics of glass surfaces and on the decided progress made b y biologies, syndevelopment of new materials and proc thetic sums and resins, compressed and esses for the industry. Frank P. Kolb liquefied gases, solvents and other synis chief chemist and Theodore J. Zak, thetic organic derivatives, and industrial assistant chemist. A series of laboratory chemical specialties, and particular recogunits are devoted to research in the fields nition should be accorded to our new of metallurgy, experimental electroplat status as an exporter of potash. ing, spectroscopy, photomicrography, and physical testing. A well-stocked library Exports of chemicals and allied products and a consulting room add to the faculties from Germany increased nearly 6 per cent of the research staff. to $200,000,000 in the first 9 months of One of the most interesting units is 1936, compared with the corresponding that in which James E. Wilson and his period of 1935. Notwithstanding numerassistant, Vernon Patterson, are engaged ous government regulations in force to in applying metallurgical equipment to reduce all imports, chemicals and allied the study of the structure of the steels products advanced 6 per cent to $65,000,000. The value gain recorded in 1936 in and alloys used in industry. The testing and control laboratory, exports was the result of advances made directed b y Ray A. Kirchmaier and in certain of the principal chemical groups, Joseph T. Anderson, is equipped for gen particularly in shipments of coal-tar eral analytical work. products, heavy chemicals, nitrogenous D . M. Webb has been added to the fèrtilizers, and explosives. Germany instaff for research in chemistry, one of his creased its exports to almost all South and immediate problems being the electroCentral American countries considerably. deposition of various metallic substances Exports from the United Kingdom as a backing for reflectors. changed less than 1 per cent and reached The manufacturing laboratory, with nearly $92,000,000 in January to SeptemGeorge C. King in charge, has faculties ber, 1936, while imports of $74,000,000 for making pitches, waxes, résine, polishing were 7 per cent above the corresponding felts, and numerous other materials refigure for 1935. quired in the plant and for sale to other After the large gains in Japanese exindustries. ports the past 3 years, only a 3 per cent
B
Larr, JAMBS E. WOSOK;
RXQBT, FBASTK P. KOLB
