I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Vol. 16, No. 6
Testing of Foam for Use on Fires’ By Clement IC. Swift MACANDREWS & FORBES Co.. CAMDEN. N. 1.
D
URING recent years
With the deoelopment of foam $re-protection systems for oil f a c t i o n . Frequently dethe use of foam in and other extra hazardous risks, the necessity of prooiding and composition Occurs in spite extinguishing fires maintaining eficient foam-producing solutions has been appreof such precaution. ciated. has undergone a notable Methods of testing the expansion. The method of This article describes the desirable characteristics of foams and quality of foam should blanketing fires with a layer foam solutions. Analytical methods applicable to solutions are follow as closely as POSof resistant foam was aPdescribed, and methods are gioen for comparing the fire resistance the conditions to which Plied Primarily to Oil fires, and other physical characteristics of foams. the foam is subjected in because no other satisfacfighting a fire. A good tory method of attack was foam must be produced available for burning oil. A layer of foam, the bubbles of in large volume, must be tenacious so as to withstand which contain carbon dioxide, when spread over the surface of mechanical abuse, must be fluid enough to flow freely over the oil, smothers the fire by cutting off the supply of air to a burning surface of oil, but stiff enough to adhere to a vertical the burning material. The use of foam has now been ex- surface when used on other fires. It must not wilt rapidly tended to combating all kinds of fires, and numerous formulas when exposed to the flames. for producing firefighting foams have been developed. The following method of testing has been developed to No standardized methods have been hitherto published cover the properties outlined above: for the qualitative or quantitative testing of the claims made SOLUTIONS for the various compounds, or for the determination of those qualities which should be possessed by a foam to be used on Foam-producing solutions deteriorate from the loss of fires. The use of foam for this purpose has now assumed carbon dioxide, and, in the case of certain formulas, from such dimensions that the publication of methods of testing decomposition of the foaming agent induced by bacterial action. I n the ordinary installation the storage tanks are becomes desirable. The materials commonly used for producing foam are not tightly closed, and consequently evaporation occurs, solutions of sodium bicarbonate and aluminium sulfate, which necessitating occasional dilution to the original standard strength. react according to the following equation: SOLUTION A-Chemical analysis of A solution is seldom Alz(S04)3 6NaHCOa = 2A1(OH)3 f 3NazS04 6C02 necessary. Since the only change that occurs in stored To either or both of these solutions a foaming agent is added, solution is the loss of water by evaporation, it is sufficiently so that the carbon dioxide evolved when the two solutions accurate to determine the specific gravity a t a standard are mixed may be retained as a mass of fine but tough bubbles. temperature and refer the value to a curve giving directly The solution containing the aluminium sulfate is designated the percentage of aluminium sulfate. The result will show the necessary dilution, or required addition of aluminium as A , and that containing the sodium bicarbonate as B. The foaming agents employed have been organic materials sulfate. SOLUTION B-The B solutions are analyzed particularly of animal or vegetable origin, such as glue, glucose, licorice extract, and saponin extract. The following are typical for sodium bicarbonate. Numerous volumetric methods formulas: have been investigated, most of which are unsatisfactory No. 1 No. 3 because of intense color of the solution. Highly diluted Solution A Per cent Solutzon A Per cent solutions may be titrated with standard acid using phenolAluminium sulfate Aluminium sulfate 9 04 phthalein followed by methyl orange, but the results have Water 87 l3 Sulfuric acid 0 45 Solution B Water 90 51 been found to be entirely unreliable. The most satisfactory Sodium bicarbonate 8 Solution B method yet developed is a modification of that proposed by Foaming agent 3 Sodium bicarbonate 6 85 Sundstrom,Z in which sodium bicarbonate is titrated with 89 Glue 1 14 Water No. 2 Glucose 0.46 o,0175 sodium hydroxide according to the following equation: Arsenious acid Solution A 11 ,7 Water 91.52 NaHC03 f NaOH = NatC03 HzO Aluminium sulfate Sulfuric acid 0.56 The end point is detected with 10 per cent silver nitrate Water 88 14 Solutzon B as an external indicator. As long as the solution conused Sodium bicarbonate 8.45 Foaming agent 1.7 tains only carbonates and bicarbonates, silver nitrate gives 89 85 Water a white precipitate, but the first traces of free sodium hyThe use of sulfuric acid in A solution accelerates the rate droxide give a brown Precipitate of silver oxide: 2AgN03 2NaOH = AgZO f 2NaN03 HzO of expansion and tends to give a more fluid foam. It is objectionable principally because of its corrosive action on The titration is made on a 25-cc. portion of the clear solustorage tanks, lines, and pumps. Also, since the strength tion, using a sodium hydroxide solution containing 0.1267 of the foam structure depends largely upon the colloidal gram of NaOH per liter. One cubic centimeter of this aluminium hydroxide in the bubble walls, the substitution sodium hydroxide solution is equivalent to 1 per cent of soof any considerable amount of free sulfuric acid for aluminium dium bicarbonate. It is necessary to carry the titration sulfate results in the production of a less durable foam. well over the end point, and permit the color to develop for The use of such foaming agents as casein, glue, and glucose several minutes on the spot plate. The first definite change requires the addition of a preservative to prevent putre2 Lunge, “Technical Methods of Chemical Analysis,” Vol. I. 1908,
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1 Received
December 11, 1923.
p. 469.
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June, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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is taken as the end point. The sodium hydroxide solution is standardized against a newly prepared basic foam solution made with freshly boiled distilled water. Unless the solution is quite clear, it is necessary to remove suspended matter by cenlzifuging or filtration. Normal sodium carbonate may be estimated by titrating the total alkali and deducting the equivalent of the previously determined bicarbonate and the alkalinity (if any) of the foaming agent. The method of titrating the total alkali will depend upon the foaming agent used in the solution, and for this reason no general method can be given.
FOAMS EXPANSION TEST-The purpose of this test is to determine the volume of foam produced from a definite volume of mixed solutions. Ordinarily cross comparisons are made using the following combinations : (1) Standard A (2) Unknown A (3) Standard A (4) Unknown A
solution with solution with solution with solution with
standard standard unknown unknown
B B B B
solution solution solution solution
For this test four 1000-cc. cylinders of approximately the sarne height are selected, and 50 cc. of the proper A solution poured into each. Fifty-cubic-centimeter portions of the B solutions are poured into small beakers. The contents of each of the beakers are poured quickly into the corresponding cylinders and the volumes of the resulting foams noted after 2 minutes. The variation in temperature between any two solutions should not exceed 2" C. The results are expressed as a percentage of the standard. This method of cross comparison gives an indication of the condition of each solution as well as of the combined unknown solutions. Check tests should not vary more than 5 per cent. New solutions prepared from a good formula should produce 10 volumes of foam from 1 volume of mixed solutions a t a temperature of 24" C. (75" F.). After standing undisturbed for 60 minutes, the foam should not wilt to less than 7.5 volumes. Stirring a t the end of 60 minutes should not reduce the quantity of foam to less than 4 volumes. QUALITY TESTS-TO determine the quality of foam produced from solution samples is exceedingly difficult in the laboratory. Numerous methods have been proposed and used, but none is entirely satisfactory. A few of the proposed methods are the following: (a) The rate of wilting may be determined by observing the decrease in volume of the foam produced in the expansion test, readings being taken a t 10-minute intervals for 1 hour. ( b ) The foam may be vigorously stirred, either immediately after reading its initial expansion, or after standing 1 hour, and the decrease in volume noted. This test is invariably made in connection with the expansion test, and gives a valuable indication in the hands of an experienced operator. However, it may lead to erroneous conclusions unless the technic of mixing the solutions is carefully standardized. (c) A weighted and calibrated stem similar to a hydrometer may be permitted to drop through the foam, the rate of sinking being observed. ( d ) The foam may be floated on a liquid such as kerosene and the rate of wilting estimated from the accumulation of water under the kerosene.
The chief objection to these methods is that foam is not being tested under anything like service conditions. The effect of time, agitation, or contact with oil may give some kind of a quality indication, but the most important test is ability t o resist exposure to fire. There is also the difficulty of generating foam under conditions approximating those on the field. Long experience has indicated the manner of mixing solutions as one of the most important factors influencing foam quality. There is a critical period between the mixing of solutions and the
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APPARATUS FOR COXPARING FIRERESISTANCE OF FOAMS
When foam solutions are compared by this method, it is quite important to vary only one factor a t a time. If, for example, two foaming agents are being compared, they should be used in the same formula as regards aluminium sulfate and sodium bicarbonate, and the age and temperature of the solutions should be the same when the test is made. Moreover, deteriorated solutions should be compared with new solutions prepared from exactly the same formulas. Fluidity. The apparatus described above may be used to compare fluidity or the spread of the foam. For this purpose the foam is discharged on an unlighted gasoline surface, and the area measured 2 minutes after discharging the solutions.
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Additional indications of foam quality are given by smallscale field tests, such as the following:
1-A small area of burning gasoline (1x 1.5 meters) may be extinguished with a hose stream and the foam permitted to remain on the surface. After standing over night the foam blanket should not be completely destroyed. 2-Foam projected on a vertical wood surface from a hose stream should cling for several minutes before sliding off, provided the layer is not too thick. 3-1f, after extinguishing a gasoline fire, the foam is carefully pushed back to expose about 400 sq. cm. of the gasoline surface, and the gasoline is reignited, the foam should be sufficiently fluid to flow back and again extinguish the fire.
TESTINQ OF PORTABLE EXTINGUISHERS The tests that have been described are intended to apply to solutions used in fixed systems rather than portable apparatus. I n the case of foam-type hand extinguishers, the only satisfactory test is to discharge the apparatus in the way it is intended to be used, observing the quality and quantity of foam and its effect upon test fires.
IMPORTANCE OF TESTS The principal cause of deterioration of solutions in fixed systems is the loss of carbon dioxide according to the equation: 2NaHCOa = NazCOs 4- COn
4-HzO
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The decomposition is accelerated by high temperatures and exposure of the surface of the basic solution to currents of air. I n portable apparatus the space above the solution surfaces is protected from air currents, and a sufficient concentration of carbon dioxide is maintained practically to establish equilibrium. The loss of gas from fixed systems results in the production of smaller volumes of foam, of less satisfactory quality. It is therefore important to make frequent tests of solutions in fixed systems, determining the volume and quality of the foam and the sodium bicarbonate content of the basic solution. The value of any foam formuIa should be judged by tests of the foam, and also by the ability of the foaming agent to resist decomposition from bacterial action. I n the past too much stress has been placed upon initial expansion, and too little attention given to foam quality and permanence of the solutions. A proper balance of all these factors is necessary to insure satisfactory results from foam fire-protection equipment. ACKNOWLEDGMEKT The writer wishes to acknowledge with thanks the valuable cooperation of Percy A. Houseman in developing the methods herein described, and in the preparation of this article.
Specific Heats of Lubricating Oi Is"' By E. H. Leslie and J. C. Geniesse UNIVERSITY OF MICHIGAN,ANNARBOR,MICH.
HE specific heats of lubricating oils, and
T
The specific heats were The specific heats of s i x typical lubricating oils have been measured determined by measuring over a range of temperatures from 37.78 to 143.33 C. (100 to 290 the rise in temperature reF.) A n increase of 35 to 40 per cent in specific heats was found. sulting from the passage I t is obvious that a change as large as this must be taken info account of a measured electrical in engineering work. The variation of specific heats with temperacurrent through a resistance ture is not the same for all oils, and it is suggested that further study coil immersed in the oil in might disclose some connection between the temperature rate of change a calorimeter. of specific heats and the properties of an oil as a lubricant. APPARATUS (FIG.1) O
of the heavy fuel oils and residuums, is a subject on which the technical literature does not offer an abundance of information. I n the design of automotive lubricating systems, of apparatus in which oil is used as a heating fluid, and of many apparatus such as heat exchangers used in the oil refinery, knowledge of specific heats of heavy oils over a range of temperature is necessary. The results presented in this paper are not those of an elaborate investigation of the entire subject. Rather, they are of limited scope and were obtained because of the necessity for their immediate use in engineering work. The nature and properties of the lubricating oils studied are summarized in Table I. The oils are products made by well-known American manufacturers,
TABLEI-PROPERTIES OF LUBRICATING OILS --SPECIFIC GRAVITY-- --VISCOSITY-TYPEO F PETROLEUM Corrected t o Saybolt Universal F R O M WHICH THE Lu6Oo/6O0 F. 37.78' C. 98.89' C. BRKCATING OILS WERB Oil As Read 15.5"/15.5° C. (100' F.) F.) MANUFACTURED . (210O . A 0.9027 a t Mixture of paraffin235.5 46.3 base and mixed-base 25O C. (77" F.) 0.9077 oetroleums 0.9320 a t 60.2 Mixed-base petroleum 2 2 O C. (71.6'F.) 0.9359 612.5 0,8900 a t 96.5 22' C. (71.6OF.1 0.8939 1190.0 0.9006 a t 199.0 45.3 22O C. (71.6OF.1 0.9045 Mixture of mixed-base 0.9160 a t 688.0 67.0 Oklahoma, Kansas, 123' C. (73.4'F.) 0.9207 a n d Texas petroleum 0.9161 a t 135.0 25O C. (77' F.1 0.9221 2385.0 1 Presented before the Division of Petroleum Chemistry a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 t o 14, 1923. 2 Part of the results presented in this paper are published through the courtesy of the Brush Engineering Association of Detroit.
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The calorimeter consists of a 500-cc. wide-mouth, vacuum bottle packed in powdered Sil-0-Cel contained in a Parr calorimeter pail. The heating element is a 61-cm. coil of B. & S. No. 24 chrome1 wire soldered t o heavy copper leads. The current for heating is drawn from Edison storage cells. The stirrer is a small brass propeller run at a constant speed of 1100 r. p. m. The thermometer is one calibrated by the Bureau of Standards and graduated to tenths of a Centigrade degree. The thermometer and leads are supported by a cork that also serves to close the vacuum bottle.
PROCEDURE In order to determine a specific heat, about 220 grams of oil were placed in the vacuum bottle. A current was then passed through the heating element and the temperature raised somewhat above the lower temperature of the 5' C. interval over which a particular set of observations was to be made. The current was then shut off and the calorimeter system allowed to cool. Readings of time and temperature were taken in order to determine the rate of heat loss. When the temperature had dropped slightly below the lower temperature of the observation interval, the heating current was again passed through the immersed resistance coil. Readings of time, voltage, amperage, and temperature were taken while the temperature rose 5" C., and then the oil was heated to a temperature 1.5"C . or more above the upper temperature
