8.j6
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
hot water, heating to boiling, cooling, and making up to volume. The solution is allowed to cool and stand overnight or longer. It is then filtered on a folded filter, returning the first turbid runnings to the filter. Filtration is slow, and several hours or overnight is necessary. The starch solution thus prepared, preserved by shaking with a little toluene and keeping in a closed flask, keeps indefinitely substantially unchanged. It sometimes becomes slightly turbid, but this turbidity may be readily removed by filtration. Method I n determining the diastatic activity of an infusion of malt, the pH of the starch solution is adjusted to 4.8 by adding Walpole's acetate buffer (8 cc. of 1 N acetic acid and 12 cc. of 1 N sodium acetate made up to 100 cc. with water) a t the rate of 2 cc. of buffer to each 100 cc. of starch solution. The malt infusion is so prepared that each cubic centimeter represents 50 mg. or a known multiple of 50 mg. The initial polarization is made by mixing 50 cc. of the buffered starch solution with 1 cc. of strong ammonia and 5 cc. of the malt infusion, mixed in a dry flask in the order named. The solution is then filtered if necessary and polarized. Five cubic centimeters of malt infusion at 21 " C. are placed in a dry flask and 50 cc. of the buffered starch solution, also at 21' C., added, counting time from the moment when the first of the starch solution reaches the malt infusion. The mixture is then allowed to stand in a water bath a t 21" C. for a time within which the polarization should not decrease more than 11.3" V. (where a 4-dc. tube is used in polarizing). One cubic centimeter of strong ammonia is then added, the
Vol. 20, No. 8
solution filtered, if necessary, and polarized. In filtering, the precautions described by Zerbaq3 consisting of rejecting the first runnings of the filtrates and keeping the funnels covered with watch glasses, should be observed. The two solutions should be polarized a t the same temperature to avoid errors due to the marked effect of temperature on the polarizations. The diastatic power is calculated from the formula, 100 D L =
t X l X c
where L is degrees Lintner, D is the fall in polarization observed due to 250 mg. of sample, t is the time in hours, 1 is the length of tube in decimeters, and c is a constant determined experimentally. c = 4.6. Notes on Method
The clear starch solution, prepared as described above from the soluble starch containing 13.25 per cent of moisture, contained 4.706 grams per 100 cc. It polarized a t 105.3" V. a t 20" C. in a 4-dc. tube, and a 25-cc. portion reduced 66.6 mg. of cuprous oxide when treated by the Munson and Walker method. Thus the specifk rotation was 194 and the reducing power expressed as per cent of dextrose was 2.43. The factor c was determined by the use of an infusion of malt, the diastatic activity of which was determined by the gravimetric Lintner method, The soluble starch used in this determination was of Kahlbaum's make, carefully rewashed and redried. The 2 per cent starch solution contained the Walpole 4.8 acetate buffer at the rate of 2 cc. per 100 cc. of starch solution. 8
Hardin and Zerban, IND. END. CHBM.,16, 1175 (1926).
Electrochemical Polarization Process for Prevention of Corrosion in Locomotive Boilers',' L. 0. Gunderson3 THECHICAGO AND ALTON RAILROAD COMPANY, BLOOMINGTON, ILL.
HE normal life of a locomotive fire box and boiler shell used in a soft or treated non-corrosive water district mag be indefinitJe, while the flues, by successive piecewelding and cutting down to fit shorter boilers, will last upwards of ten years or until worn thin from the fire side. Under these conditions general overhauling of the boiler is made necessary only by federal requirement in interest of safety once in four years, unless an official extension is granted. This overhauling consists of removing and reapplying the flues, examining and renewing n few stay bolts, anti other minor repairs, and generally costs only a few hundred dollars. In a corrosive-water district we may find that fire boxes will last only a comparatively few years, in some localities oiily two or three years, representing a loss of from $2000 to 53000 depending on the size of the locomotmire. During this period the locomotive in such corrosive-water district will have had two sets of flues destroyed by pitting and
T
1 Presented before the Division of Water. Sewage, and Sanitation Chemistry at the 75th Meeting of the American Chemical Society, St. Louis, M o . , April 16 t o 19. 1928. 2 Some details of this process have been noted by the author, Ry. Rev., September 24, 1926; Proc. Pittsburgh Ry.Club, April 28, 1927; A m . RY. Eng. A s m c n . Bull., 29, 135 (1927); Proc. Western K y . Club, March 19, 1928; and by Carrick, J . A m . Water Works Assocn., 19, 704 (1928). 8 Present position, chemical engineer, Electro-Chemical Engineering Corporation, Chicabo, Ill.
grooving, representing an approximate loss of $1200 to $3200 for the two sets of steel flues, in addition to the loss of a few hundred dollars due to scrapping flue sheets and stay bolts that would be destroyed by corrosion. Recently the writer had a close check made of the cost of renewing the belly of a Pacific type passenger locomotive, made necessary because of corrosion in form of grooves and pits after only four years' service. The cost of labor and material was $2150, which included stripping the boiler aud removing it from the frame, all made necessary by corrosion, although the actual cost of the corroded material was less than a hundred dollars. These figures demonstrate the involved character of corrosion in locomotive boilers, where the actual loss is only fractionally represented by the cost of the material. It has been estimated that the railroads of the United States spend 12 to 15 million dollars annually to repair boiler material destroyed by corrosion. To make a correct diagr,osis of cases of corrosion in locomotive boilers is no simple matter, especially on road engines that use a large variety of feed waters on a division. This and other variables make locomotive boiler corrosion a problem much more involved than corrosion in stationary powerplant boilers. In the same water district some boilers will pit and groove primarily a t the forward end, where feed water is injected wit,h more or less oxygen content, and the fire-box end will
August, 1928
INDUSTRIAL AND ENGINEERING CHEMISTRY
not be affected, nhlle other boilers using the same batrr in identical service will show severe corrosion in the fire-box end. The variations seem to be due to differences in rate of circulation and temperature of the injected water. Injected water a t abnormally low temperatures will retain oxygen longer in solution and thus contribute to fire-box and rear-end corrosion by permitting oxygen to be carried back by the circulation
On the wntrr's road selere corrosion resulting in flue failure from pitting iri less than a year's time has taken place in locomotive boilers wing feed waters treated to excess caustic alkalinity (10 5 pH). To account for this rapid corrosion it may be assumed eitlier that the hydrogrn-ion concentration is increased under boiler coi,ditions of pressure and temperature or that this n a t w shpply and ninny others on the road must possess pronoiiiice 1 film-dckti oying power3 effective in caustic boiler water. Thermal-Generated Electric Currents in a Locomotive Boiler
867
determined by a millivolt-milliammeter, was 2.0 millivolts, the boiler shell being electropositive, evidently because the pipe was covered with ferric oxide formed while serving as an anode in the protection system. As the boiler was fired up, the potential difference was reversed, the pipe becoming electropositive, and with increasing temperature and pressure the potential difierence increased proportionately until a value oi 1.5 volts was obtained, which gave a flash amperage of 3 amperes across the boiler-water electrolyte. A pronounced electric spark was obtained by making and breaking the circuit. Upon continued shorting of the pipe and the boiler shell the above values rapidly diminished to 25 millivolts and less. These figures refer to the boiler standing st.ill with no steam used nor water injected. The ariicr attributes this rapid reduction to the polarization by hydrogen deposited on the boiler shell, causing the potential of the t\vo surfaces to approach equilibrium. Breaking the circuit for a, few minutes permitted the electromotive force to be rebuilt approaching t,he original values. Moving tlie engine caused an immediate marked increase of the loner dues. Headings taken on a Pacific type passenger locomotive over a 127-mile division showed mean value of i50 millivolts and a constaiit flow of 2 to 2.5 amperes from pipe to boiler shell., These values were maintained throughout the trip. Constant sparks could be obtained by alternately malting and breaking the circuit.. On a switch engine in Hloomington, Ill., yards using very corrosive boiler feed water, a fairly constant value of 600 millivolts and a maintained current from the pipe to boiler diel1 of approximately 1.5amperes was rrcorded over a period of 30 minutes. V7hen the locomotive stood still and used 110 steam, these values rapidly decreased, indicating increased po1:iris:ition. Running the headlight generator had no effcct on these values.
The possibilities of thermal-gencratcd elect.ric currents in a locomotive boiler and their effect on pitting and corrosion
hive been overlooked almost entirely in recent corrosion literature. The destruetiori wrought by stray-currrnt electrolysis on pipe lines adjacent to street railways that have not well-bonded returns is generally apprechtrd. Is it t,hen consistent to disregard consideration of pssilile destructive electrolysis currents in a locomotive boiler? Tlie pioneer work'of Burgess4 is well worth reviewing. Hr denionstrated very satisfactorily that heating the boiler metal niade it electropositive to the irnlieated metal, the poiential difference incrcasing s::mewliat pmport,ionntely with the increase in temperature. In a 1i-inch experimental boiler under 85 pounds st.cam bresdure tie found a potentixl difference of 3.9 millivolts bet,ween the hot jnner tube and the cooler oiit.er shell and recorded a current flow of 19.3 milliuinper- through the boiler-water electrolyte, and he foulid thut this current in a few hours caused pitting apparent t o the naked eye, The magnitude of these values in a locomotive under 200 pounds steam pressure (387" F.) is surprising. Tlie writer has not completed t.he test with a boiler tab:. owing to the difficulty of maintaining insulation under tlie high pressure and excessively hot combustion gases in tlie fire box. which burn off even metal projections protruding from the back flue sheet.. However, lie used onc of tlie 1inch ivroiight-iron pipe anodes (18 feet long) of the cloctrochemical system to be subsequently described, which pipe is located near the top of the boiler, submerged in the boiler watcr, and perfectly insulated from metallic contact Nit,h tlie boiler. I t extends nearly the length of ilic boiler flues. When tlie boiler was filled with cold boilrr water, the potential d3erence between the pipe and the boiler shell, as
Method of Determining Th~rmsl-ElectricCurrents Generated in e LOcOmOfi".? Boiler
The comparatively high amperage across several inches of boiler-water electrc1yt.e seems out of proportion to tlie voltage; wherefore the writer advances the opinion that wine of this current was picked UII from the hotter flues bexrath. thP pilie being the shortest route of less resistance for this current. When a temverature difference of less than 140" F. between the flue (&7' F.) and the boiler shell ( Z O O F. estimate) can create such electromotive force values and magnitude of current as here recorded. the writer can anticinate what, Iir might find when he insulates a flue conveying hot, gwex ~~~
Tvons. A m . Elrifrochcm.
Soc., 13, 17
(1908).
Ih’DUSTRIAL AND ENGINEERING CHEMISTRY
868
of approximately 1000” to 1500” F. The only reason that such electromotive force represented by potential differences between hot and cooler portions of the boiler is not utterly destructive to the hot portions is that the metal-to-metal elcctrical contact a t both ends of the flues permits the current to be released through the circuit-flues to front flue sheet, to cooler boiler sliell, to lower firebox portions and back flue sheet, returning I 1 t o t h e b a c k end of flues. No o n e will deny that these thermal zenerated electric
recorded on the pas: senger l o c o m o t i v e ,
i r o n woiild.be corroded away in 24 hours and, since this corrosion is never uniform but in pits, the rate of penetrating the pipe will be propordionately rapid. Previous Electrolytic Methods of Corrosion Prevention The foremost methods of trying to reduce or prevent pitting and grooving in locomotive boilers are: overtreatment of feed wat.er to high excess caustic alkalinity, partial de-aeration of feed water by open-type heater, and the electrochemical method. Of the various attempts to prevent corrosion in boilers, electrolytic means are among the oldest. Sir Eumphry Davy, in 1823, used iron and zinc to protect tlie copper sheathing of ships; but as the bottoms fouled hadly by marine growths on the clean copper surface the scheme was abandoned. In 1833 he applied his famous zinc “protectors” as an electrolytic protection against corrosion in boilers and condensers. Since his time the application of this method of clectrolytio protection has been advocated and t.ried with conflicting result,s, some condemning and some commending the application of zinc slabs attached to the boiler or condenser metal. The troubles experienced with zinc were poor contact and rapid destruction of zinc. There are indications that the use of an externally applied electric current occurred to Sir Humphry Davy, but since electric generators were not yet known, it was not thought feasible to use an expensive installation of primary c e k to supply the necessary current. I n 188g6 Dolby described an electrolytic system applied to hoilers, using insulated electrodcs extending into the water of the boiler, and an alternating current supplied by a magneto. The claims were that the alternate plating out of oxygen and hydrogen would cause these elements to recombine to form a thin film of water, which would prevent scale formation. A few years later Wurtze described a method of protecting mine equipment, boilers, etc., by electrolytic means. An electric current from directcurrent dynamo was passed through the electrolyte from anodes inserted therein, making the materials to be protected the cathode in the corroding solution. Since that time many patents have been issued on electro* Pror. Inrl. Cluil Xnb. (London). 99. 88 (1889). 8
Eng. Mag., 7, 297 (1x94).
Vol. 20, No. 8
lytic methods and installations and on various types of electrodes used for insulating the anodes from the boiler shell, but practically the only generally known and tried system was that of Elliott Cumberland as described in United States and British patents of 1908 t,o 1912.’ Another type of so-called electrolytic system for the alleged prevention of scale and corrosion in boilers is represented by numerous patents in late years in this country and Europe, and consists essentially of a few wires and contacting points connecting together electrically the hotter portion of the boiler, such as the dome, and some colder portion, such as the blow-off cock, with or without the use of an electric current of very small magnitude (only a few millivolts) generally derived froin a thermocouple located at a hot portion of the boiler. One of thesc systems has a vibrator or interrupter in series with the tiny electric current. If there is any plausible scientific explanation for the alleged effect on scale and corrosion of short-circuiting an electric current though tlie boiler metal between points, the writer has not learned of it. Even this syst,em is old. Woods mites: An acid-incrustor was extensively experimented with by one of the leading railways of t h e United States, when a few wires and
the gal;anic action excited by the use of impure water, tl&w down the impurities, one and all, ready to be blown off. The use of zinc plates to help out was then resorted to, and finally zinc plates alone were used, and this electrolytic system disappeared. Just as the use of zinc plates had its advocates and denouncers, so the electrolytic system with an appliod electric current supplied to insulated anodes has had a varied reception in thc engineering field, the recorded failures of t h e system a b o u t balancing its s a t i s f a c t o r y performances. Its early promoters seem to have been as much concerned about scale prcvcntion as corrosion prevention. Its successes in corrosion prevention appear to be confined to condensers, and its failures are outstanding in boiler installations, where we know the corrosion problem to be most complicated. The breaking down of t h e insulation has been suggested as the Interior View of Boiier of Engine NO. 49 Equip e d with Electrochemical cause of the failure of &tern, ai Monfha’ Service in the system to protect Very Corrosln Water Territory. Note Good Condition of A n o d e boilers from corrosion. especially in forms of destructive pitting. However, upon close analysis there is no more reason why pitting should cease when the boiler metal is made a cathode in an electric circuit than that. local galvanic action should cease on the zinc plate of a primary cell io service. which battery men early recognized as a serious problem and which they solved by amalgamating the plate. The reason for the protection that amalgamation afforded the zinc plate from cor-
,
U . S. Palenfs 948,968 sod 1,020,980; British Patents 8422 (1908). 8068 (1900). 19,837(1911). and 4251 (1912). I( Tronr. Am. So
