TIEFT: OLD STYLE I,AXJNDRY WITH
BATTEHY OF \vOoDEN \%'ASHERS. R I ~ X T SEvEnAL : DEPARTMENTSOF A b ~ o D E R NLAUNDRY INSTALLATION-A REAL TEXTELC PROCESSING PLANT
Detergency of Alkaline Salt Solutions IV
Laboratory Comparison in Simulation of Laundry Practice FOSTERDEE SNELL,305 Washington St., Brooklyn, N. Y.
E
XPERIMENTAL work has already been published proper amoimt of acidity in the soil, and interfacial tension (Parts I to 111 of t h k series) comparing various against greasy soils and deflocculating and emulsifying factors in detergency: degreeof alkalinityasmeasured power are considered in the relative ratio which applies in by pH and Cot, (IO), wetting power as measwed by inter- commercial practice. That work was entirely with unbuilt facial tension between the detergent solution and a blended soaps so that the results touch those recorded here in only oil containing knonn small amounts of free fatty acids (SO), one place. The results are applicahle to laundry operations and deflocculating and emulsifying power (Sf). While these to only a limited extent, because laundries build their soaps, factors arc known to eontribute to the detergent action of with the exception of a few minor classifications of work. alkaline salts, ~ i t l and i without soap, there is no assurance Later Rhodes and Bascom (16)publislied results on soaps that other factors do not contribute also. The relative built with sodium hydroxide, trisodium phosphate, sodium importance of tho different factors varies in different de- carbonate, and borax. As their data do not show the units of tergent applications and is to some cxtent a matter of opinion. soil removed, they are not available in R form comparable There has been a sustained effort over a period of years to with these data. They concluded that nraximum efficiency devise an experimental procedure which would compare all in washing was obtained a t pZf 10.7, a maximum which these of the factors in their proper relative proporhns. Attempts data fail to indicate, although no special effort was made to to suspend a pigment in tho detergent solution using the parallel their work so as to check that maximum. formation of foam as an end point (4)or to filter a deflocculated soil (5, 13) did not give satisfactory comparisons. EXPERIMENTAL METHOD Determinatioii by chemical means of the amount of mangaThe Rhodes and Brainard nretlrod consists in soiling nese dioxide suspended in the detergent solut,ion was not, satisfxtory (6). The relative importance assigned to different ilesized cotton shcctiting with a soil composed of lamp black functions of an alkaline salt solution was probably altered too '2 grams, lubricating oil 5 grams, tallow 3 grams, and carbon greatly in t l ~ s procedures. e tet.rachloride 2000 cc. The soiled and dried fabric is washed Experirricntal washing procediires varying from hand- in the form of hags containing glass beads in a miniature laundering to miniature and full-size wash wheels have wash wheel at constant temperature for a standard period of utilized BS soils indigo (8, fa),fruit juice (15),tea (15),claret time. The wheel contains 500 ec. of the detergent solution (f5),oil (%), a mixture of flour, meat juice, albumen, lemon and is revolved at 80r.p.m. After the fabric is washed,it is juice, burnt flour, fat, milk, mustard, and burnt onion (M), rinsed in a number of standard rinsing solutions and dried in ferric hydroxide (@), and ultramarine ( I % ) , as well as mix- an oven at 80' C . for 60 minutes. Finally, the brightness tures of various oils and charcoal, carbon black, or lamp- of the fabric so treated is measured in a special photometer black (1, 9, If, 14, f7,18, %$). None corresponds or can and compared with the brightness of the original c1ot.h. The method has been amplified by Morgan (f4),chiefly correspond to the complex soil deposited on naturally soiled with respect to the soiling procedure. He suggests a soil fabrics. While the early part of this experimental work was under formula (lamp black 2 g a m s , Nujol 10 grams, Russian way, Rhodes and Brainard (17) published a method for tallow 3 g a m s , and carbon tetrachloride 2000 cc.) as being comparing detergent power by washing tests under stand- less likely to change in composition over a period of time. ardized conditions. I n their method the relative importance As a further improvement he has devised a method of imof neutralizing value can be approximated by the use of a pregnating the fabric with this soil by mechanical means 1240
November, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
1241
rather than by hand. I n this cent. U s i n g this cottonseed Experimental washing by a mod$ed Rhodes and way he impregnated f a b r i c oil, the free fatty acid content Brainard procedure gives reproducible results in the more u n i f o r m l y and more of the soil was 0.095 per cent. same laboratory. A soap builder alone is primarily i n t e n s e l y . He claims that T h e d i r t e n c o u n t e r e d by a detergent only to the extent that it can react with greater sensitivity is thus obl a u n d r i e s i s m a d e up of a free fatty acid in the soil to produce soap. Sectained. He has also suggested number of types of material, with respect to the construcan important one of which is ondarily it may be effective because of improved tion of the miniature w a s h fatty m a t t e r . F a t t y acid wetting power of the detergent solution. One of the wheel that all parts be made would be present accordingly, important functions of a soap builder is to speed u p of monel metal and that the and the reaction which would detergency. This may be expressed as a measure mechanism provide for occur between such acid in dirt of the rate qf removal of soil. Under specific conreversal of the wheel in the a n d a n alkaline b u i l d e r t o manner of laundry wash wheels. form soap is one of the ways ditions with low acidity of the soil, 0.1 per cent The wheel c o n s t r u c t e d by in which a builder exerts deeach of soap and soda ash is less eficient than 0.1 Rhodes and Brainard revolves tergent action. It is thereper cent soap atone, and 0.1 per cent each of soap in o n l y o n e direction. Refore desirable to use a soiling and metasilicate is more eficient than 0.1 per cent versal of the wheel in laundries mixture which will resemble soap alone. This cannot be expected to hold for all is to prevent the clothes from ordinary dirt in this way and balling up. The specimens are which will allow for such reacacidities of the soil. so prepared that there will be tion with the b u i l d e r . The I t is desirable that the hydroxyl-ion concentration no danger of the test specipresence of 0.095 per cent of of the builder solution be relatively large and the men becoming entangled in a free fatty acid in the soil should sodium-ion Concentration relatively small. miniature wheel of this sort. fulfill such a specification, alBased on several factors, the order of decreasing Morgan obtained data which though this concentration is indicate t h a t decreasing the much less than that actually value as detergents of the builders studied is: sodium number of reversals slightly o c c u r r i n g in ordinary dirt. orthosilicate, sodium metasilicate, a mixture of increases the amount of soil Two batches of the m i x t u r e sodium metasilicate and soda ash, sodium hyremoved. were made up approximately droxide, modijied soda, and soda ash. The beT h e m i n i a t u r e washing 2 months apart. No variation machine constructed for this havior of colloidal soap builders is clearly dismas found t o occur b e t w e e n work was similar in all respects these two batches or in either t inguishable from that of noncolloidal soap builders. to that described by Rhodes batch after standing for some Acidity of dirt increases the ease with which it and Brainard. time. is removed. The soil used in these exThe soil mixture as prepared The theory is advanced that the ejgciency of the periments was similar to the above was applied to Utica Mills two above with modification different builders with soap is some positive power of sheeting having a thread count only to the extent necessary of 90 X 94, which had been dethe number of units of brightness regained in washsized by laundering twice in a to p e r m i t comparison w i t h ing. I t is estimated as not less than the second, or c o m m e r c i a l l a u n d r y . The previous experimental work. brightness of this fabric before greater than the third power. The major factors in It contained c a r b o n black 4 and after desizing was 83 per cent detergency are mechanical action, wetting power, grams, m i n e r a l oil 5 grams, as compared with a standard magnesia block. Before soilcottonseed oil 3 grams, and cardejlocculating power, and emulsifying power, the ing, the desized cloth was cut bon tetrachloride 2000 cc. It latter two possibly appearing under ,another name. into strips 10 X 20 cm. The was prepared by grinding the method of applying the soil was The data arc! in agreement with the micelle theory of carbon black in the mineral oil slightly different from t h a t of detergency. Rhodes and Brainard. About and cottonseed oil in a mortar, 100 cc. of the soil solution were The detailed data presented here are on builders washing out with carbon tetraplaced in a 6-inch (15.2-cm.) chloride, filtering three times and soap in one ratio. When similar data in other evaporating dish. The strip of through four layers of cheesefabric, held with f o r c e p s , was ratios become available, whether from this or other passed through the solutionthree cloth, and diluting to 2000 cc. laboratories, practical results in the laundry will be times each way, t u r n e d over, with carbon tetrachloride. A and again assed through three predictable with much greater certainty. f e w l u m p s of carbon black times eacf way. It was then were retained by the cheeseplaced on a sheet of aluminum and rolled with a rubber roller, cloth and these were broken &st' on one side, then the other. u p w i t h a s t i r r i n g r o d and It was dried in an oven at 8O0$3.for 1 hour and aged 16 hours at washed through with carbon tetrachloride used for dilution. room temperature. Five strips were soiled at one time, fresh The carbon black used was a very finely divided carbon soiling solution being taken from stock for every batch of five black toner which was found to be preferable to lampblack stri s. The four most uniformly soiled strips were selected from because less trouble was encountered with formation of eacf batch and the fifth was discarded. Throughout the duration of the experiments the soiling procedure was always carried aggregates in the suspension. The mineral oil was Miner's out by the same man. He was able t o obtain fairly uniform soilneutral oil from the Sinclair Refining Company, a grade ing, the variation from the standard of 40 per cent brightness as since altered in name to Cadet oil. It is refined from a compared with a standard magnesia block never amounting to Pennsylvania crude and has a specific gravity of 0.84 and i more than one per cent in either direction. Rhodes and Brainurd soiled to a brightness of 30 per cent, with slightly greater variaSaybolt viscosity of 50 seconds a t 100' F. (37.8' (3.). The tion. In either case the extent of soiling represents an extreme cottonseed oil, used in place of tallow, had a free fatty as compared with actual laundry conditions. The standard of acid content of 0.38 per cent. Assuming that Rhodes and 40 per cent rather than 30 per cent was chosen because it allowed Brainard used an edible grade of tallow, its free fatty acid of greater uniformity between the soiled strips. This method soiling embeds some of the dirt so deeply that it is not recontent would not have been greater than 0.05 per cent, of moved in the experimental washing procedure. The soiling ia making the acid content of the total soil not over 0.017lper representative of a soil difficult rather than easy t o remove.
A
1242
I N D U S T R I A L A pr' D E N G The washing procedure was the same as that of Rhodes and Brainard. The strips were sewed around the edges to form bags 10 X 10 cm. Just before closing, 100 grams of 5-mm. glass beads were placed in each and sewed in. Two such bags were prepared and washed at one time. They were placed in the apparatus with 500 cc. of the detergent solution to be used and the whole brought to a temperature of 40" C. The cylinder was rotated a t a speed of 80 * 5 r. p. m. for a washing period of 10 minutes. Rhodes and Brainard found a 7.5-minute washing p e r i o d to give the maximum effect, but it is p r o b a b l e that this was a function of the part,icular soil used. Morgan ( I C ) found no such maximum to exist. A 10m i n u t e period was t h e r e f o r e adopted as more convenient and fairly representative of laundry practice. T h e r e i s one noticeable discrepancy b e t w e e n the method and u s u a l laundry p r a c t i c e . This is in the ratio of soiled fa b r i c to wash solution. In FIGURE 1. COMPARISON WITH RESULTS a typical commerOF RHODES AND BRAINARD cial laundry 150 t o 160 gallons of water are used in the first operation, or break, and about 60 gallons in the following suds operations for 300 to 350 pounds of flat work. In the break the fabric absorbs a great deal of water so that the actual wash water is considerably less than 150 gallons. The ratio of fabric to wash solution, therefore, ranges from 1:1.5 t o 1:4.0 by weight. In contrast t o this, in the miniature wash wheel the ratio of fabric t o solution, disregarding the glass beads, is approximately 1:145 by weight. The practical result of this difference is t o permit of the removal of a much greater amount of soil in one laundering operation in a laboratory way than can be removed in practice with the limited amount of detergent solution available t o carry away the dispersed soil. There is no reason to believe that in operating on a small weight of fabric with a large amount of detergent solution the relative importance of various detergent factors other than neutralizing value for acid soil is altered. The degree of soiling of the detergent solution by the test specimens is probably as great as of wash solutions in laundry practice, because of the much greater amount of soil present per unit weight of the test specimen. Rinsing was carried out by hand and consisted of five dips in a series of beakers containing 500 cc. of the following solutions in the order named: (1) detergent solution, of the same concentration as used in the washing operation, at 40" C.; (2) distilled water at 40" C . ; (3) distilled water at 40' C.; (4)acetic acid, 0.05 N solution, a t 40" C.; (5) distilled water at 40' C. After opening and air-dryng for one hour, the bags were ironed wlth a cool iron. The color was then read and the entire washing operation repeated. At least four successive washings were run on each bag and the results recorded. The photometer used by Rhodes and Brainard for measuring the brightness of the soiled and washed strips was a special type not available in the open market. In order to permit the use of a standard instrument, the Ives Tint Photometer was used in this work. The Ives instrument can be used for reading either gray stains in terms of total brightness or colored stains in terms of the red, green, and blue components. The use of the Ives instrument permits the extension of the experimental work to colored siliceous soils such as umber or ocher. In order to avoid inaccuracy in reading the brightness because of any slight unevenness of soiling, the fabric to be measured was tightly stretched on a motor-driven turntable, which was mounted in the housing
I N E E R I N G C H E hl I S T R Y
Vol. 25, No. 11
of the tintometer. The turntable was revolved at such a rate that no detail of the fabric was visible. Readings were taken
from two separate portions of the revolving fabric and the two values averaged. These two readings usually checked within 1 unit of brightness or better. Two bags were run at a time and a t least two runs were made for each determination. Each final value, therefore, represents the average of two runs, each of which is the average of four readings. The final values are estimated to be accurate within 0.25 unit of brightness. The results are primarily expressed in terms of the units of brightness regained by the cloth as a result of the washing procedure-that is, the difference between the percentage of brightness of the soiled strip and the percentage of brightness of the same strip a t the completion of the procedure outlined. MATERIALS COMPARED
The builder materials included in the comparison by this method were sodium hydroxide, sodium orthosilicate, sodium metasilicate, sodium carbonate, modified soda, and a commercial builder containing 41 -34 per cent of anhydrous sodium metasilicate and 25.3 per cent of anhydrous sodium carbonate. The tallow soap used was Flake Amber soap from Procter &- Gamble Company. Rhodes and Brainard found no advantage in increasing the concentration of soap in the detergent solution above 0.10 per cent. Morgan found the optimum maximum concentration t o be 0.25 per cent. A concentration of 0.1 per cent has been used in the previous experiments in this series. This is the concentration considered practical by the Laundryowners National Association of the United States and Canada. It was adopted for this work as fairly representative of 1a u n d r y practice and as likely 2o t o show a greater effect of added builder than P a higher concentration. This is in accordance with the results of Fall (6). An equal concentration of soap builder was adopted, although in some of the previous No. ofI Washer experiments 0.033 per cent s o l u t i o n s were 1 2 3 4 wed* It is the prac- FIGURE2. EFFECTOF MATERIALS tice in many laundries IN 0.1 PER CENTSOLUTION AS COMto use equal amounts of PARED WITH DISTILLED WATER soap and builder. This is in excess of the amounts of builder usually recommended. Interfacial tension determinations have shown that in 0.05 per cent solutions a 1:l ratio of soap t o builder is more effective than a 3:l ratio in the case of the more highly alkaline builders.
RESULTS To indicate the correlation between results in this paper and those of Rhodes and Brainard, Figure 1 gives data plotted on the same basis. The runs using distilled water alone and those using soap alone are the only points of contact of the two sets of data. Bearing in mind that the soil used in this work was different, the curves give a basis for qualitative comparison of results published in the two papers. Some of the points of difference are as follows: RHODES AND BRAINARD Age of soil, hours Degree of soiling, units Mineral oil Black Saponifiable matter Fatty acid content of nonvolatile soil % Time 'of washing, min. Soap concn., %
11 To 30 Lubricating Lampblack Tallow Estd. as not over
0.017 7.5 0.25
SNELL
0.095 10 0.10
November, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
Their data have been taken with as high accuracy as possible from rather small-scale curves. Their curve slopes mare gradually, indicating that equilibrium with the detergent solution was reached more slowly, presumably because of lower fatty acid content. They removed more total units of soil because their fabric was coarser and more highly soiled with a dirt which was probably coarser. Considering all these factors the results are surprisingly similar in trend. To give a general picture of the individual effect of the materials used, Figure 2 shows the results with tv-o builders, with soap, and with distilled water. With soil, time, speed of rotation, and temperature constant it is reasonable to suppose that the effect of water is a constant measure of the effect of pounding alone. Results n-ere limited to four washes early in the work because pilot results indicated that any effective detergent solution showed no perceptible effect n-ith the soil used in these experiments after the fourth n ash. This would not necessarily be true with a different soil but the relative locations of the curves could be expected to be the same. Since the effect of pounding is so great, Figure 3 presents the data on a different scale with the effwt of water alone subtracted from each curve. If nothing else is shown, these data clearly indicate that a builder alone has not the effectiveness of soap when used independently. Also, TT ithout the effect of pounding in the wash wheel-that is, with the effect of distilled water alone subtracted-alkaline salts of themselves show substantially no effect after the first operation. This indicates that they are primarily effective in the removal of soil by reaction with its fatty acid and by their effect on the soap. The d a t a obtained I: __-__I from t h e runs m a d e F //-with soap and builder together are shown in " Figures 4 and 5 on the 8 - i --Taiiow Soap same scales. It is in$ ..,.__._... 5odaAsh dicated from these that _. -5adivm M e t a i l l i r a t e sodium orthosilicate is best, followed b y 4-7 s o d i u m metasilicate, ,,,,,_,..........._. .. .................." then by the blend of ,;),.. ;... .-.-._.-.-. soda a s h and m e t a ,.:'./. 1 No.ofWashcr I silicate. Sodium hydroxide reaches a high I 2 3 4
/ I/ /
/
,(
1243
meaning that the same relationship would hold a t a different ratio of builder to soap. An interpretation of these data can be made on the assumption that the cleansing action of soap is due to micelles rather than t o large soap aggregates. Soap alone has a definite effectiveness. When builder is added, the factors become more complicated. The data are not to be interpreted as i n d i c a t i n g t h a t under all c o n d i t i o n s soda ash is detrimental to soap solutions and metasilicate h e l p f u l . A factor occurring i n practice which is not d u p l i c a t e d in these laboratory experiments is the ratio of detergent s o l u t i o n to f a b r i c . Therefore, the demand made on the builder in terms of neutralizing value in these washes is much below that in FIGURE4. COMPARISONOF SOLUp r a c t i c e . What the TIONS CONTAINING 0.1 PER CENT data do mean is that, EACH OF BUILDERAND TALLOW Soap provided acid soil did n o t h a v e t o b e removed, metasilicate would be helpful and soda ash detrimental in those concentrations. THEORETICAL
DISCUSSIOY
Detergency has been favored with a great deal of work on individual phases. The interrelation in quantitative terms of the factors involved is obscure. To some extent, soap formed a t the interface between the dirt and the detergent solution serves to suspend the dirt. This is primarily a function of the degree of alkalinity. Any alkali present tends to convert fatty acid in the dirt t o soap. The extent to which such conversion progresses in a given time is a function of the degree of alkalinity as measured by COH. The principal equilibrium is probably as follows in which S represents the fatty-acid ion: HS
+ OH-
HOH
+ S-
An alkaline builder furnishes a relatively large sodiumion concentration. Given y, the ionized sodium soap, 20, the nonionized sodium soap, and 2, the hydrolyzed sodium soap (not appearing in the equation), the effect of addition of X sodium ion is to drive the partial equilibrium to the right: XXa+
+ yNa+ + yS- + wNaS
$
NawS-u+y
+ XNa+ + yNa+
This would be the expected effect of additional sodium ion. For convenience in comparing, Table I lists the various builders with their possible moles of sodium ion (assuming complete ionization), possible moles of hydroxyl ion (assuming complete hydrolysis, or, in the case of caustic soda, only ionization), and the moles of hydroxyl ion present estimated from p H values in 0.033 per cent solution. TABLEI. SODIUMAND HYDROXYL IONSIN 0.033 PER CENT SOLUTIOSS BUILDER Sodium hydroxide Sodium metasilicate Sodium carbonate Modified soda Sodium oleate (0.1%)
LIMITINQVALUELIMITINQVALUE HYDROXYL ION FOR Na ION FOR OH ION FROM PH VALCE Moles per liter
o.oos2 0.0024 0.0062 0.0051 0,0033
0.0082 0.0024 0.0031 0.0017
....
0.0071 0.0016
0.00045 0.00010 0.00016
INEERING CHEMISTRY
Vol. 25, No. 11
builder. This would follow because the ideal builder would remove all but the deepest seated dirt in the first bath. This was approached in some of the results quoted. I n the later baths the effect of pounding to bring deep-seated dirt near the surface would be the only factor. The poor detergent would have some surface dirt yet to remove and show a greater removal in the later baths. The total removed by the efficient detergent would be greater than by the poor one. As a measure of the detergency to be expected from a given alkaline salt, the percentage of the total brightness regained under the conditions stated was tentatively adopted. As this is not sufficient to define a detergent completely, an index for the speed of detergency was also required. This is the uercentaee of t h e total brghtness regained in four ...... washes which is obtained i n t h e first
gency'obtained with distilled water a l o n e . B o t h are obtained w i t h 0.1 per cent of builder
12 0
g
4
,/.;/ /
/ ' ;/
/ , . a
...-..
_..__
--01*Tauaw5LUp
1 4
_._......_I 5 v d a Ash + 011*50ap
I
NootWnhn
I
a s a function of C O H and CNA.would take
d....
.
-..._
___ .._.........
M.t~.il;~.t.-Sad.A.hBl.nd CeusticSoda b d i t x sods Soda Ash 01% bllw Soap Added to All Bullden
v a l u e obtained other than by the b u i l d e r and, as has been done
BUILDER WITH 0.1% AMBERSOAP Sodium orthosilicate Sodium metasilicate Commercial builder Sodium hydroxide Soda ash Modified soda
UNITEOF BRIGHTNESS DEINDEXO F REGAINED Next TEBGENCT SPEED o? 1st wash 3 waehes INDEX DETSRGENCT 12.12 11.26 10.63 9.75 7.56 7.60
None 1.00 0.75 2.13 1.44 2.38
% ._ 40.4 40.8 37.9 39.6 30.2 32.9
% 100.0 91.8 93.4 82.0 83.4 76.0
Sodium orthosilicate is so effective that after the first bath it is no better than distilled water. This means that the pounding effect in the wheel is practically the only factor operating after the first wash. Sodium metasilicate and the commercial bIended builder approach this condition, giving relatively little effect in the second, third, and fourth washes. Soda ash is next, with caustic soda and modified soda showing the greatest effects in these later baths.
EVALUATION OF DETEROENCY FXOU~B Up to this point the absolute units of brightness regained COMPARATIVE RATESOF REMOVAL IN INDIVIDUAL WASHES have been considered as a measure of detergency when a If the virtue of a soap builder is that it removes the dirt soiled fabric is washed with soap and/or builder. Those more readily, there should not only be greater removal of figures have been taken as linear values. There are indicadirt in one bath by it than by a less efficient builder, but the tions from commercial use that such an assumption is not dirt removed in the later baths should be less with the efficient correct.
November, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
1245
COMPARISOK WITH IKTERFACIAL TENSION, ALKALIKITY, The assumption is made that the brightness of the fabric AND EMULSIFYIKG POWER is a measure of the number of dirt particles present. That is only partially true. Doubtless the obscuring power of At this point it seems desirable to make a limited comeach added particle decreases as the fabric becomes darker. parison of the present results, which are designed to include As a factor opposed t o that, doubtless the particles removed the various factors of detergency, with earlier, more specific first tend to be removed more easily than those removed series of results. Such data for a limited series of builders and later. These two tendencies are opposing, and for the sake for soap are given in Table 111, and for builders and soaps of simplicity it is as- together in Table IV. *.-. 7-7 1 sumed for the present TABLEIv. SUMhL4RY OF TESTSON SOLUTIOXS O F SOAP WITH : / ADDEDBUILDER alance. (Values in parentheses are estimated approximations) If each d i r t parEMULSIALSAFYING ticle was carried in LINITY INTER- POWER WABEINGTESTS (0.1% PACIAL (0.1% s u s p e n s i o n by one (0.1% SOAP + 0 . 1 % SOAP+ T E K S I O NSOAP ~ + molecule or micelle BUILDER, 40' C.) 0 . 0 3 3 % (0.033% 0.1% 4 B U I L D E R , BCILDER, BUILDER, ____..'. of soap, a linear ratio /-.' ___..... . 1 wash washes 25' C.) 40' C . ) 20° C . ) would be the correct Units of brightness Mg. umber/ regained p H Dynes/cm. 100 ce. e v a l u a t i o n of the ----s>dhm
Ortharilicate
two molecules or micelles, the square of the u n i t s r e m o v e d would be the correct 3 I 2 value since one parFIGURE7. COMPARATIVE EFFECTOF atta&ing itself BUILDER AND SOAP SOLUTIONS OVER would haye the same THATOF DISTILLED WATER chance as before, but (In term8 of the aquare of units of brightneas the second one would regained) have only a chance represented by the square root of the number of such particles present. This, expressed conversely as the units of brightness regained, would be the square. Similarly, if three molecules were required it would be the cube root and the cube. Without going into any greater detail, this is simply another expression of the familiar mass action law where the probabilities of AB are expressed by (CA X CB)/CAB= K , but the possibilities =, K', and AE, as of AD1 are expressed as ( C A X C D ~ ) / C A D ( C A X C B * ) / C A B=~K"'. It is possible that by suitable estimate of the number of particles of carbon black present in the soil and the number of soap molecules present in the solution, some estimate would be formed. It is equally possible that the values so obtained would be absurd and that the form in which soap was present in solution would be required for interpretation. If the average form of soap in the concentration studied is bimolecular or trimolecular, that would permit of raising the ratio of soil particles to soap molecules to a larger figure without raising the poFer of the equation accordingly. This would be the case because each aggregate or micelle would be one unit. As an estimate which is not, based on any specific experimental evidence, the power is probably of the order of the second or third.
'
21.00 Sodium hydroxide 23.50 Sodium orthosilicate 22.50 Sodium metasilicate 18.81 Sodium carbonate 18.75 Modified soda Distilled water 11.25 Dimmig pipet against benzene
11.9 24.50 24.75 (11.6) 11.3 24.88 11.0 21.69 10.3 22.50 12.63 (5.6) free fatty acid.
+
