October, 1929
INDUSTRIAL 9 S D ENGINEERING CHE;MISTRY Literature Cited
(1) British Standard Reference Dope, British Engineering Standards Assocn., Report 83; also specifies ingredients t o be used, ( 2 ) Calvert, IND.E s c . CKEM.,21, 213 (1929). (3) Collischonn and Ruppert, U. S. P a t e n t 1,109,512 (1914). (4) Cross and Bevan, TJ. S.Patent 530,826 (1894). ( 5 ) Gardnrr, Knauss, and Van Heuckenroth, IND.E N G . CHEM., 21, 57 (1929). (6) Gardner and Whitmore, I b i d , 21, 226 (1929). (7) Hibbert, I b i d . , 13,256,334 (1921). (8) Hofmann and Reid, I b i d . , 20, 687 (1928). (9) Keyes, I b i i i . , 17, 1120 (1925). (10) Leduc, Heitz 8- Co., British Patent 21,426 (September 28, 1911); C. .,I.,’’/, 1108 (1913).
965
(11) Mardles, J . SOL.Chem. I n d . , 42, 128T (1923). (12) Martens, M i t t . kgl. ~ ~ u l e r i a l p r i i i u n g s a m 29, t , 57 (1911); J . SOC. Chem. Z n d . , 30, 44 (1911); C. A , , 6, 2943 (1911). (13) Ost, Z . anger;’. Chem., 32, 66, 76, 82 (1919). (14) Schutzenberger, Compl. rend., 61,485 (1865). (15) Schwalbe, Z . u n g e v . Chem., 24, 1256 (1911), finds t h a t hydrolysis must precede actual acetylation. (16) Sproxton, “Cellulose Ester T’arnishes,” p. 46 (1923); discussion of theTe catalysts. ( l i ) Sproxton, I b i d . , p , 156. (18) Wolff, “Die naturlichen Harze,” p. 218 (1928). (19) Wolff, I b i d . . p. 309. (20) n’orden, “Technology of Cellulose Esters.” Vol. I , P t . 4, (21) Worden, Zbid., p . 2987.
Experimental Application of Automatic pH Recorders to Sugar-Refinery Alkalinity Control’ A. L. Holven CALIFORSIA A X D HAWAIIAX S C G A R REFIXINGCORPORATIO-h.,CROCKETT, CALIF.
The possibility of replacing colorimetric hydrogenwash birup used for mingliiig H E importance of a ion control of sugar refinery products by a centralized raw sugar, ( h ) raw liquor a t close regulation of hyautomatic control based on pH recorders has been the melt, (c) all products prior drogen-ion concentrainvestigated. t o cloth filtration, (ti) prodtions in sugar manufacture The chief obstacle to such an application is the lack ucts entering char filter\, ( r ) cannot be overemphasized, of a suitable continuously indicating electrode. Alh i g h - g r a d e pan sirupb, (E) a s t h e r e is b u t a narrow though the bare-wire tungsten electrode in combinas w e e t w a t e r s n i t h i i i the range of pH between sufficient tion with a calomel half-cell appeared the most promisacidity to cause large losses evaporators, (9) sludges from ing of a number of combinations tested in various t,hrough sucrose inversion and Sweetland filters prior to filrefinery products, this electrode proved to have the alkalinities which accelerate tration over Oliver filters. following objectionable characteristics: (1) variation A11 of these products, except glucose destruction, and the of calibration with variation of composition of sugar development of c o 1or a i i d sludges, are niaiiitained beproduct under control; (2) not readily interchangeable, melassigenic liniwalts. t n e e i i p H 7.00 and 7.30. because of individual differences of characteristics; This is clearly a proinisSludges are kept bet~veeiipH (3) lack of permanence; (4) sensitiveness toward poiiiig field for automatic coii8 00 a n d 9.00 to facilitate soning. trol. Progress in this directheir filtration. Until a more reliable type of indicating electrode, tion has been somenkit, slow, A s about thirty to forty requiring fewer replacements and less attention, is hoivei-er, because of inany products are c o n t i n u o u s l y developed, the general application of pH recorders to obstacles, some of which fire limed by this qystuii, a rather refinery alkalinity control appears impractical. peculiar only t o the sugarelaborate control i- necessary. refining industry. Although The ba4s of regulation conthe results of the esperimeiits reported in this paper 1iaT.e si-ts of the spot test method in conjuiiction with a set of not \-et led t o a successful application of automatic pH permanent colorimetric pH standards. The addition of lime apparatus for this purpose, it is hoped that some discussion to the various products is regulated by the station operators, of thein may lead to further developments along this line. under superviiion of an alkalinity controller who inalces rounds of the entire refinery regularly. testing about thirty Review of Previous Developments products per hour. As a background to this discussion, a brief review of refinery That this system has been quite effwtive is evident from alkalinity control as developed by this company may be de- the fact that products are now maintained in a practically sirable. neutral condition throughout the refinery by the use of only Originally. only the products entering the refiiiiiig process about 50 per cent as much lime as was required under the were limed. L-nder such circumstances procluct,s were over- previous system, thereby minimizing both iiiverqion and limed at’ the st,art of the process, but became seriously acid molasse3 production. during later stages of refining. Further Improvements in Hydrogen-Ion Control The disadvantages of such a practice were quite apparent, and in 1922 this organization made an exhaustive study of When the above system of control was introduced in 1923 the subject’ for the purpose of correction, and instituted a ( 3 ) )consideration was given t o automatic control, but this system of alkalinity control which has been in successful n a q abandoned as no electrode suitable for industrial use operation for the past six years. had been developed. However, the advantages to be gained Briefly, this system consists of a circulating liming system, by an automatic control which would entirely eliminate the whereby a thin lime suspension (about 2 ” Brix) can be coii- personal element 111 the liming of thirty t o forty products tinuously added to all of the following products in order t o are so obvious that all developments in this field h a r e been neutralize acidity as promptly as developed: ( a ) affiliation followed n i t h great interest since that time. During the past few years several electrodes which ap’ Presented before the Division of Sugar Chemistry a t the 77th Meeting peared to offer fair possibilities for this nork have been deof t h e American Chemical Society, Columbus, Ohio, April 29 t o M a y 3, 1929.
T
veloped. Such electrodes have been discussed by Parker (6,6) and the work of Paine, Balch, and Keane (1, 2 ) indicated that both the tungsten and the quinhydrone electrodes functioned satisfactorily in some types of sugar products. I n view of these recent developments, investigation of the possibilities of, automatically controlling the hydrogen-ion concentration of refinery products was resumed in this laboratory. This investigation consisted of a preliminary laboratory study of the characteristics of various electrodes and the experimental application of a tungsten-calomel electrode assembly and pH recorder to refinery control.
on a refinery sirup (Table I) whose actual pH was 6.25 by the standard hydrogen electrode. The unreliability of the quinhydrone electrode in solutions above pH 7.0 is shown by a series of tests in which a refinery product was adjusted to various hydrogen-ion concentrations (Table 11). Table 11-Actual
pH a n d pH by Quinhydrone Electrode PH INDICATED ACTUAL B Y QUINKYDRONE ‘ PH ELECTRODE 6.75 6.70 7.00 7.06 7.25 8.00 8.00 8.54 8.75 9.22
.
Characteristics of Various Electrodes
The laboratory work consisted mainly of a study of various types of electrodes, as it was recognized that the lack of a suitable indicating electrode would be the principal obstacle. 94.
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I
I
I
While the work of previous investigators had indicated that tungsten electrodes were fairly satisfactory in the control of cane-juice defecation and in the second carbonation of beet juices, the application of such electrodes to cane refinery products touched on a new field in which sirups of practically any density, purity, and character of non-sugars are encountered. Note-As an illustration of the diversified character of refinery products, it may be of interest to note that in the use of the hydrogen electrode the time required to reach equilibrium varied from a few minutes in some products to several hours in others.
Four electrodes appeared to offer fair possibilities. T o ascertain which would be the most satisfactory, each type was tested in various refinery products. After the preliminary tests, all except the bare-wire tungsten electrodes were discarded for reasons as outlined below. (ZUINHYDROXE ELECTRODE-considered from the standpoint of a continuous indicator, the quinhydrone electrode was found to have three undesirable characteristics, namely(1) tendency for readings to drift; (2) unreliability between pH 7.00 and 8.00, and inaccuracy above pH 8.00; (3) diEculty in the continuous introduction of quinhydrone into the flowing liquor. Table T-Readings of“ b y Quinhydrone a n d Standard Hydrogen Electrode Showing endency of Quinhydrone Readings to Drift TIME ACTUAL PH PH BY DRIFTERROR Q U I N K Y D R O N ~B Y STAHDARD ELECTRODE HYDROGEN QUINHYDRONE OF QUINHYDRONE IH SERVICY. ELECTRODB ELECTRODE ELBCTRODE Minulrs Negligible 6.26 0 6.25 + O . 13 6.38 6.25 5 + O . 18 6.43 6.25 10 +0.22 6.47 6.28 15 +0.26 6.51 20 6.25 +0.30 6.55 6.25 25 +0.33 6.58 6.25 30
The extent to which the electrode readings drifted from the true value in a 30-minute period of use is evident from tests
ANTIMONYELECTRODE-Another electrode with which a few experiments were conducted was the antimony electrode, the use of which in the paper industry had been very favorably reported by Franke and Willaman ( 4 ) - This work was abandoned when it was found impossible to prepare antimony electrodes giving reproducible results. The cause of the erratic behavior of the antimony electrodes in refinery products has not been determined, but is believed to be in some manner associated with variations in crystallization of the antimony during casting of the electrode. TUiYGSTEN-Mn& ELECTRODE-The results obtained in preliminary tests with this electrode immediately indicated that it was valueless for this work, as it failed to hold its calibration. This conclusion was substantiated by several series of tests on various products. Table 111, showing the extent to which the pH indicated by the tungsten-manganese sesquioxide electrode differs from the actual pH indicated by the standard hydrogen electrode, illustrates this lack of permanence. Table 111-Comparison TIME TUNGSTEN-MnzOa
ELECTRODE SERVICE Hours 4 24 28 70 166
IN
of pH b y Tungsten-MnaOa a n d Standard Hydrogen Electrodes ACTUAL PH BYSTANDARD PH INDICATBD HYDROGEN BY TUNGSTENELBCTRODE MnaOa ELECTRODE 7.50 7.50 7.50 7.50 7.50
7.60 7.00 7.10 8.80 7.20
BARE-WIRE TUNGSTEN ELECTRODE-ASthe bare-wire tungsten electrode appeared to be more promising than any of the others, it was thoroughly tested in a variety of refinery products. A peculiar characteristic indicated by these tests was that the calibration of the electrode is markedly influenced by the character of the product in which it is used. This is evident from the graph in Figure 1 which shows the potentials developed by the tungsten electrodes in a number of products adjusted to various hydrogen-ion concentrations. The fact that the calibrations of the electrode in various products are practically parallel makes it easily possible to compensate for this variable by impressing on the tungstencalomel electrode assembly sufficient potential to place its calibration a t any desired point on the recorder paper. This method of compensation is outlined in a later section. The results of laboratory tests indicated that, even though the calibration of the bare-wire tungsten electrode is dependent on the refinery product in which it is used, it appeared to be the most satisfactory of any of the electrodes tried and was therefore incorporated in the experimental recording equipment. Practical Application of Recording Equipment,
To secure definite information regarding the practical operation of pH recorders in the plant, experimental equipment was developed and tried out on four refinery products
October, 1929
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When using this assembly for continuous service, a regvlar routine was developed for care of the electrodes. It was necessary to flush out the calomel cell with saturated potassium chloride solution, and to renew the potassium chloride crystals and saturated solution in the porous cup every 2 or 3 days. The tungsten electrodes were found to require much more care than the calomel electrodes. I n accordance uitli the usual practice, the electrodes were activated by soaking in a solution of tribasic sodium phosphate for about 2 days and were then sensitized toward the product in which they xere to be used by 2 dags' immersion therein before being placed in service. I n operation, two tungsten electrodes were used in parallel service-one electrode being replaced each day or sooner if check determinations showed that it gave erratic readings. When a new electrode 1m.s placed in service, it was not connected to the recorder until tests showed that it properly indicated the pH value. The electrodes removed from service were carefully cleaned and regenerated in the sodium phosphate solution before being returned to service. Eight electrodes were used, and a continuously rotating service was maintained. I n general, the electrodes would not give satisfactory continuous service for more than one day. Figure 2-Arrangement of Experimental pH Recording Equipment
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R
of diversified character-namely, raw liquor, &nation wash sirup, specialty liquor, and Oliver filtrate. As the nomenclature differs with each refinery, a brief description of these products is given here: Raw Liquor. A 66' Brix solution of washed raw sugar having a purity of 99 degrees or higher. Ajinatian Wash Sirup. Dark viscous sirups of about 70' Brix and 80' purity. The affination sirups contain the bulk of the impurities washed from the raw sugar. Specialty Liquor. A water-white liquor having a purity of about 99.5 degrees or higher, and a density of about 66" Brix. Oliver Filtrate. This is the filtrate from the Oliver continuous filter in which the regenerated kieselguhr is dewatered. The filtrate is essentially a very dilute solution of inorganic salts leached from the kieselguhr. The sludge is preferably kept a t about pH 9.00 in order to facilitate filtration.
Subsequent discussion will consider each of the above products from the standpoint of operation of equipment and results attained. T e s t s on Raw Liquor
As the equipment used on raw liquor is of rather general application and was used a t each of the other experimental installations, its essential features will be described in some detail. RECORDIKG EQUIPMEST-The instrument used throughout this investigation was a special Leeds and Northrup recording potentiometer, having a range of -250 to $550 millivolts. As this recorder is fundamentally the same as the pyrometer-potentiometer, its principles are familiar. This particular instrument was originally calibrated in millivoits, but was later recalibrated directly in pH units for convenience of the operators. ELECTRODE ASSEMBLY-The reference electrode in this set-up was the usual saturated calomel half-cell, which made contact with the solution through a porous cup filled with potassium chloride solution. The bare-wire tungsten electrode acted as the indicating electrode. The electrodes were arranged in a glass flow chamber, through which the sample was passed to make contact with both tungsten and calomel electrodes. The arrangement is illustrated in Figure 2.
SAMPLING EQUIPMENT-Raw liquor in the melt house is maintained a t a density of about 66" Brix and a temperature of 80" C. As raw liquor usually contains a small amount of fiber and other foreign matter, it was screened before being sent to the electrode chamber. It \vas difficult to find a screen entirely suited to this purpose. If the mesh was suficiently small to remove practically all suspended matter, the screen quickly clogged and prevented the flow of liquor. On the other hand, a screen of too large ti mesh would pass sufficient material to foul the electrodes quickly. The most satisfactory solution of this problein was found t o be a screen pot containing a perforated copper plate having 400 holes (0.0025-inch) per square inch. The raw liquor was drawn from the vent line of a centrifugal pump through the screen pot and a cooler. The main cooler consisted of a copper cooling coil enclosed in a cylindrical
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Figure 4
chamber about 4 inches in diameter and 12 inches high. As a further means of cooling, the sample was passed through two glass condensers connected in series. The cooled liquor flowed by gravit,y through the electrode chamber and back t o the main melt tank, as illustrated in Figure 2. -4s the liquor cooled, its increased viscosity retarded flow through the apparatus. This difficulty was oaercoine by installing a water connection whereby the liquor was coiitinuously diluted to approximately 50" Brix, as previous experiments had shown that this amount of dilution had no appreciable effect on the p H of the liquor. COMPESSATION FOR T'ARIATIOM IF TEXPERATURE AYD CHARACTER OF PRODUCT-&the characterist,ics of the harewire tungsten electrode are affected bot,h by changes in temperature a i d by variations in the charact'er of the product in which it is used, it is necessary t o compensate for these variables if the readings are to be recorded in p H unit's. During this experimental work devices for accomplishing both types of compensation were developed in this lahoratory. TEXPERATURE ComEssaTIos-The t'einperature coefficient of the bare-wire tungsten electrode is about' 2 inillivolts per degree change in temperature. Compensation for temperature fluctuations was obt'ained by connecting, in series n-ith the electrodes. a thermopile d i o s e temperature coefficiciit was exactly equal hut opposite to that of the tuiigst,en electrode. A siiitable thermopile for t'liis purpose consisted of a series of fifty copper-constantan thermocouples. I n operation with the recorder, the thermopile is so connected that whenever a fluctuation in temperature causes a change in t,he potential difference of the electrodes there is ai1 equal and opposite change in the potential of the thermopile. The hot juiiction of the thermopile is iinmerped in the flowing sample, n.hile t,lie cold junction is maintained a t a substantially constant temperature by packing in a Thermos bott,le filled with kieselguhr. This device i-ery effectively eliminated the T-ariations due t,o temperature fluctuations. Its general arrangement is illustrated in Figure 3. PRODUCT COMPEKSATION-ASthe potential of the barewire tungsten electrode is dependent not only on the pH but also on the character of the product in which it is immersed, it is necessary to compensate for the voltage fluctua-
tions caused by differences in conipositioiis of the samples in order that' the potentials of t,he tungsten electrode will give the proper readings on a chart calibrated in pH units. The graphs included in Figure 1 show that the difference between the potentials of the hngsten electrodes in any two prodiicts a t the same p H value is a constant. For example, the potential of a tungsten electrode in raw liquor a t any p H is 12 millivolts greater than that of the same tungeten electrode in S o . 555 liquor a t the same pH. It follows that if a recorder particularly calibrated for raw liquor is used on Yo. 555 liquor, all readings will be about 0.3 pH unit (12 millivolts) too low unless means are provided for increasing the potential difference of the tungstencalomel electrode assembly used in the S o . 555 liquor by 12 millivolts. A small auxiliary potentiometer and dry cell, in series with the tungsten-calomel electrode assembly, provide a simple device for securing this result. When used on So. 555 liquor, for instance, the auxiliary potentiometer was E O adjusted as to add 12 millivolts to the potential difference of the tungsten-cnlomel electrode assembly, the resulting readings thus being properly aligned on a chart originally calibrated for raw liquor. Similarly, when using the recorder 011 S o . 2 reiiielt sugar liquor, the auxiliary potentiometer was adjusted to impress a negative potential of 7 . 5 millivolts in order to align the readings properly. Although this device is not entirely automatic, it provides a convenient and accurate nieaiis of compensating for variations in character of the product. When check cleterminations show that the recorder is not reading properly, it requires but a moment to adjust the auxiliary potentiometer by a sufficient amount to bring the calibrations to the proper position. Where a multiple pH recorder is to he used, such compensat,ors vould be of considerable advantage in bringing all records to a standard calibration. RESULTS-The results secured in the operation of the pH recorder on raw liquor were more promising than those obtained n-ith any other product. A typical record is shown in Figure 4-A. The close agreement between electroinetric and colorimetric results is shon-n by the check determinations in Table IV. I t is evident from these results that the recorder can he read t o a greater degree of accuracy t'han
ISDUSTRIAL A S D EXGINEERING CHEMISTRY
October, 1929
the colorimetric method now employed. However, the colorimetric method of control appears to be sufficiently accurate for the operator to maintain a close regulation of liming during normal operation of the raw melt. As there is only a slight fluctuation in pH of the raw liquor during normal operations, this test was not entirely conclusive. An experiment in which the raw liquor was defecated with both lime and phosphoric acid gave the opportunity for a much more thorough test. PH B Y
SAMPLE
Table IV-pH PH B Y
of Raw Liquor PH B Y
RECORDERS P O T TEST
SAMPLE
PH B Y
RECORDER SPOT TEST
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This dilution of a highly buffered product such as affination sirup causes no perceptible change in its pH value. Figure 4-B is a typical record of the pH of affination sirup, and the results in Table V show the close agreement between the colorimetric and the electrometric systems of control. SAMPLE
Table V-pH of Affination Wash Sirup PH B Y PH B Y PH BY P H BY RECORDER S P O T TEST S A M P L E RECORDER S P O T TEST 7.25 9 7.10 7.10 7.25 7.28 10 7.23 7.12 7.10 7.10 11 7.40 7.10 7.33 7.25 7.10 12 7.20 7.14 7.10 7.25 13 7.13 7.18 7.10 7.24 7.25 14 7.10 7.10 7.22 7.25 15 7.08 7.00 7.21 7.25 16 7.05
The pH of affination sirup, like that of raw liquor, can be closely regulated by the present colorimetric method of control. Tests on Specialty Liquor
Figure 4 4 shows a typical record secured by the recorder during this special defecation test. I n this case there was a large rariation in pH and the recorder closely followed each change. Where variations of this magnitude are likely to be encountered, this equipment may serve as a valuable means of both regulating and recording the pH values. As a step in this direction an alarm system consisting of a batteryoperated bell was attached to the recorder. The recorder contacts were arranged so that the bell rang at both the high and low pH limits of the product. This was of considerable assistance to the operator in regulating the lime. It would be necessary to go but a step further to use such contacts in automatically regulating the addition of lime by means of an electrically operated valve. Tests on Affination Wash Sirup
f i n a t i o n wash sirup in the melt house is ordinarily maintained a t approximately 58" Brix a t 65" C. The experimental installation was practically the same as that used for raw liquor, except that the sirup was passed directly to the cooler without screening, as it contained practically no insoluble matter. To reduce its viscosity the sirup was diluted to about 30" Brix by the direct injection of cold water.
When the tests on raw liquor and affination sirup had been completed] the experimental equipment was installed on a specialty liquor line. Specialty liquor, it will be remembered] is a water-white product having a purity of about 99.5 degrees or higher. As the pressure in the specialty liquor pump fluctuated considerably, a stand pipe was installed t o furnish a constant gravity head. After considerable investigation, both in the laboratory and a t the station, it was found that the results given by tungsten electrodes in specialty liquor were practically meaningless. Their potentials fluctuated greatly even though the pH of the liquor remained practically constant. The cause of this erratic behavior has not been ascertained, but the supposition has been advanced that it may in some manner be associated with the extremely high purity of specialty liquor and its consequent lack of electrolyte and buffer substances. Tests on Oliver Filtrate
It had been hoped that an automatic measurement of the pH of the filtrate from a regenerated kieselguhr Oliver filter would serve as a basis of regulating the alkalinity of the sludge for the purpose of facilitating filtration. Experiments in this direction gave very disappointing results, as
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within a few hours after being placed in service the tungsten electrodes would become coated with a very thin film of siliceous scale, which entirely destroyed the sensitivity of the electrode. This circumstance practically eliminates the tungsten electrode or any similar type of electrode from further consideration for use in scale forming products.
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Literature Cited 1148(1928). (1) Balch and Keane, IND. ENO. CHeM., (2) Balch and Paine, Ibid., 80, 318 (1928). (3) Blowski and Holven, Ibid I 17, 1263 (1925).
[t; ”,:::,~Ibid.,~ (6) Parker,
87 (1928).
~ d , w ~ ~ ~ ~ ~ $ ~ ~ ~ j ; 19, 663 (1927).
Chemistry in Incandescent Lamp Manufacture’ W. J. Bartlett INCANDESCENT LAMPDEPARTMENT, GENERAL ELECTRIC COMPANY. NELAPARK,CLEVELAND, OHIO
EDITOR’S NoTE--We are pleased to join, through the publication of this special article, in “Lights Golden Jubilee.” The exact fiftieth anniversary of Thomas Alva Edison’s successful experiment falls on October 21, 1929, and we take this occasion to unite in the world applause to our fellow member.
only. Argon is not used alone in lamps of general service voltages on accountof arcing difficulties. L~~~~ containing argon may be operated a t a higher efficiency than those containing nitrogen, so it is desirable to use the highest possible percentage of it. Both argon and nitrogen are obtained from the air, the INCE this year marks the fiftieth anniversary of the founding of the incandescent lamp industry, it may be former by distillation of liquid air and the latter by removing interesting to review briefly some of the things which oxygen from the air with hydrogen. This is done by the chemistry has done to help bring lamps to their present state lamp manufacturers a t a central point, from which both of development. Other branches of science have played nitrogen and the argon-nitrogen mixture are shipped in important parts, but this paper will describe those accom- steel cylinders to the lamp factories. Also, the gases are run plishments on which chemistry has through a purification process to rehad a definite bearing. move impurities such as hydrogen, The lamp manufacturer is faced oxygen, and carbon dioxide. with the usual problems in connection Just before the gases are used for with the materials of which his prodfilling lamps in the factories, they uct is made. He must deal with are further purified. From the cylintungsten, molybdenum, nickel, copders the pressure of the gas is reper, brass, and other metals. Glass duced to 60 pounds per square inch for lamps is a problem in itself. In and passed successively through a addition to the materials which actubrass tube containing caustic soda or ally appear in lamps, a wide variety potash, a similar tube of phosphoric of materials is used in processes anhydride, a heated (550” C.) iron incidental to lamp making. The tube filled with copper, and a similar manufacture of incandescent lamps tube of copper oxide also heated to is a highly developed art, most of 550’ C. The gases are cooled and the operation being done with autothe pressure reduced to 15 pounds matic machinery. This necessitates p e r s q u a r e inch and then passed close control of the uniformity of through two glass tubes, the first conmaterials, much of which is of a taining caustic soda or potash and t h e s e c o n d phosphoric anhydride. chemical nature. After this purification they are piped Tungsten to the lamp-making machines, where Thomas A h a Edison, Inventor of t h e First Practhey are still further dried by passTungsten (6, 6, 7) for incandestical Incandescent Lamp ing through several tubes of phoscent lamp filaments is obtained from wolframite ore imported from China in the form of concen- phoric anhydride. They are then ready to be used in trates containing approximately 70 per cent tungstic oxide. lamps. A number of methods for extracting the tungstic acid from Owing to the extreme importance of having pure gases the ore are in use. One process involves extraction with hot with which to fill lamps, most of the lamp manufacturers caustic potash solution to form potassium tungstate, which is have developed purification systems of their own. One converted into tungstic acid by treatment with hydrochloric uses silver oxide instead of copper oxide in a system similar acid. I n another method caustic soda is used as the ex- to the one described above, another treats the gas with tracting agent, the tungsten being converted successively into metallic sodium, and still another absorbs oxygen with a sodium tungstate, calcium tungstate, tungstic acid, ammonium solution of hydroquinone. The object in each case, however, paratungstate, and tungstic acid, the last step being ac- is to remove as completely as possible all impurities, but complished by ignition. Tungstic acid is reduced to metal especially hydrogen, oxygen, and water. by heating in hydrogen. Getters
S
Gases
A mixture of argon (85 per cent) and nitrogen (15 per cent) is used in most gas-filled lamps. A few types, especially those designed for high-voltage service, are filled with nitrogen 1
Received September 3, 1929.
The word “getter” ( I , 2, 3, 4, 8, 9) has become a rather general term to designate any material which, when placed inside of a lamp, assists in the clean-up of residual gases or reduces the blackening of the bulb. Getter in one form or another is used in practically all incandescent lamps. The
