Sept., 1 g r 6
T H E J O C R A T A L O F I N D C S T R I A L A X D EA’GINEERING C H E M I S T R Y
A CONTRIBUTION TO THE CHEMISTRY OF LAUNDERlNG I-THE RESULTS OF RELATIVE SURFACE TENSION MEASUREMENTS OF SOLUTIONS OF SOAP AND OF SOLUTIONS OF SOAP AND VARIOUS ALKALIES1 By H. G. ELLBDCZ A X D J. J. ISHERWOOD Received May 3, 1916
During t h e course of a n investigation of t h e various wash-room reagents which are employed in power laundries, t h e senior author was called upon t o make a comparative s t u d y of various alkalies a n d alkaline mixtures marketed under t r a d e names. Among those examined were found sodium carbonate, mixtures of sodium carbonate a n d bicarbonate, mixtures of sodium carbonate and borax, trisodium phosphate, mixtures of disodium phosphate a n d borax, a n d a mixture of 3 per cent soap, 6 . 3 per cent caustic soda, 8 . 7 per cent soda ash, 3 6 . 3 per cent sodium silicate a n d sodium aluminate, a n d 4 5 . 7 per cent water. Under various t r a d e names, these materials were sold t o t h e power laundry t r a d e , each with ext r a v a g a n t claims as t o its excellence above all others. T o t h e purchaser who desired t o know t h e composition thereof, t h e y were usually composed of a “sodium base” and mystery in equal proportions. T h e mystery was really resolved by a priori knowledge, t o t h e satisfaction of t h e writers. Herbert Jackson2 h a d shown t h a t t h e values of t h e alkaline carbonate, trisodium salts of weak acids-sodium phosphate a n d borax-were equal when chemically equivalent weights were considered, a n d t h a t sodium bicarbonate was either valueless or, within t h e limits of his observations, one-fiftieth of t h a t of t h e others mentioned. It seemed desirable, however, t o secure more evidence of a quantitative nature. Then, t o o , it was regarded as important t o obtain quantitative d a t a regarding t h e suitable proportions of alkali a n d soap t o be used, a n d t o demonstrate clearly to launderers t h a t because of t h e hydrolysis of soap in dilute solutions, t h e use of a certain quantity of alkali in excess of t h a t required t o precipitate t h e calcium a n d magnesium salts, is indicated b y reasons of economy. These considerations induced t h e work reported in this communication. T h e apparatus used was t h a t described b y H . W. H i l l ~ e r . ~This apparatus consists of a j cc. capacity dropping pipette with capillary stem, which terminates with a perfectly p l a n e surface, I O mm. in diameter, upon which t h e drops form in a b a t h of kerosene. The reservoir containing t h e kerosene is equipped with an overflow in such a manner t h a t t h e drops of t h e aqueous solution sink t o t h e b o t t o m a n d are discharged: leaving t h e kerosene undisturbed, throughout t h e experiment. A glass beaker was used for a water b a t h t o control t h e temperature. Acknowledgment is hereby made for D r . Hillyer’s courteous’ advice on t h e construction of t h e apparatus a n d for his communication of certain precautions regarding 1 Presented a t the Urbana Meeting of the American Chemical Society, April 20, 1916. 2 “Cantor Lectures.” 1907. 3 J . A m . Chem. SOL.,25 (1903). 5 1 1 . 524, 1256.
793
t h e necessary manipulation in counting t h e drops. -4 0 . 4 per cent solution of soap was made with distilled water and a good grade of commercial chipped soap, which, upon analysis, was found t o be free from excess of alkali, A 0 . j per cent solution of sodium carbonate was made u p from calcined sodium bicarbonate a n d distilled water. Solutions of trisodium phosphate, sodium hydroxide a n d sodium bicarbonate were made equivalent t o a 0 . j per cent sodium carbonate solution, in order t o facilitate t h e preparation of t h e solutions t o be tested. A field was plotted, with soap solutions as ordinates, in 0 . o j , 0 . IO, 0 . I j! 0 . 2 0 and 0 . 2 j per cent, and t h e alkalies as abscissa in units of 0 . I O , 0 . I j , 0 . 2 0 a n d 0 . 2 j per cent. Solutions of t h e percentages indicated b y each intersection were then prepared a n d t h e drop number was read for t h e temperature of 100’C. The results obtained are indicated in Fig. I. 0.25
0 20
0.15
a 0 0.10
0
co
*3
0.05
L
2 0.00
Lampblack is a substance very comparable t o street dirt. I t is composed of finely divided particles of carbon, associated with various hydrocarbons which may be condensed on them. The same description is applicable t o t h e smoke resulting from furnaces wherein bituminous coal is used. By placing weighed amounts of lampblack on filter papers of uniform texture, treating t h e m with equal volumes of t h e various solutions of alkali a n d soap, a n d weighing t h e filter papers with t h e residue of lampblack t h a t was not washed through, we were able t o show more or less quantitatively, t h a t solutions of t h e highest drop numbers would, under standard conditions, carry through a filter paper (S. & S. No. 589) t h e greatest amount of lampblack. Water a n d t h e solutions of alkalies used would not t a k e any of t h e lampblack through. I t was therefore concluded t h a t solutions giving t h e highest drop number have t h e greatest detergent value with respect t o unsaponifiable dirt. This conclusion lends support t o t h e contention of a number of investigations since t h e theory of
T H E J O c‘ R N A L 0 F I N D U S T RI A L A N D ELVGINEERING C H E M I S T R Y
7P1
Chevreul has been disproved, t h a t alkaline solutions are in no sense detergents in the absence of free f a t t y acids or soap.’ Water solutions of sodium hydroxide, sodium carbonate and trisodium phosphate. in t h e concentrations studied. showed very little changes in drop numbers with alterations in concentration. Within t h e limits of error of our observations. t h e changes in surface tension were about the same for chemical equivalents of the three solutions mentioned. The d a t a for all are about as shown for sodium carbonate in the bottom row of Fig. I . Along with the facts mentioned, these results show t h a t within the field examined t h e greater t h e quantity of alkali added t o a soap solution, t h e better t h e detergent properties. This is limited in practice b y the harmful effects on fabrics of large concentrations of the hydroxyl
Vol. 8, N O . 9
droxide is of no practical interest, because it is, for obvious reasons, seldom used in power laundries, These facts indicate t h a t , of t h e alkaline salts of weak acids, one is as efficient as the other as a wash-room reagent, excepting. of course, sodium bicarbonate, which. in cold solutions, does not affect t h e drop number of soap a t all. This conclusion is in harmony with the findings of Jackson, cited above. From the foregoing data, one is able t o eliminate all of the mystery in the “trade name” washing sodas mentioned. This is a preliminary report on work being conducted in t h e Rlellon Institute of Industrial Research for the Laundrymen‘s National Association of America, and it is the intention of the authors t o study further the field outlined above as t o t h e effect of these solutions on the breaking strength of cloth. M E L L O N INSTITUTE O F I N D U S T R I A L
RESEARCH
PITTSBURGH
300
,
,
,
,
,
,/‘
i1G.E
,
Effe cts of
Equivalents of Sodium Car bonote, Ti-isodium Phosphate and Sodium Hydroxide on +he Drop Number3 of Soap Solu+ions
a t 100‘ G . All AlKalies used
in Concentrations Equivoient 0.1 per
to
cent
Sodium Carbonate.
Not
tbbe compared
numerieaMy data ;n
Per
whh
FIG 31
cent Soap
ion; Faragher has shown t h a t these effects are almost negligible in t h e case of sodium carbonate and cotton. u p t o a I per cent solution of sodium carbonate. provided careful rinsing is employed. This figure is from j t o I O times t h e amount usually employed in power laundries. I n Fig. I1 there are shown t h e effects of equivalents of sodium carbonate, trisodium phosphate and sodium hydroxide on the drop numbers of soap solutions a t a temperature of 100’ C. Because of a change in the dropping pipette, these d a t a are not t o be compared numerically with those presented in Fig. I , b u t they show t h a t the values of equivalent weights of sodium carbonate and trisodium phosphate arc equal, while t h a t of sodium hydroxide is different within the field studied. The case of sodium hy1 See Faragher, Rogers and Aubert’s “Industrial Chemistry,” 2nd Ed ; Hillyer. O p . cif.. and Jackson, O p sit.
NOTES ON SOME PHYSICAL CHARACTERISTICS OF PIGMENTS AND PAINTS By HENRYA . GARDNER
Received August 4, 1916
HIDING POWER O F PIGMENTS
The opacity or hiding power (covering ability) of a paint pigment depends upon its fineness, refractive index, and oil absorption. These physical properties are responsible for the fact t h a t a coat of white lead in oil hides a dark surface better t h a n a coat of silica in oil. FIXEXESS-Paint pigments. if produced i n sufficiently large size particles, would be more or less transparent like a lump of glass, since all such products allow the light t o be transmitted in varying amounts. If any one of them, however, is broken down and powdered, the finely divided particles reflect t h e light in all directions and only a small amount of light is transmitted; the powdered substance thus appears opaque. Therefore, it may be stated t h a t the opacity of f i g m e n t s increases with fineness of division. With some pigments, however (produced b y t h e fume process), there may be a point beyond which increasing fineness may result in a lowering of opacity. REFRACTI0P;-The refractive index of a pigment determines t h e amount of light t h a t will be transmitted b y it. The higher the refractive index. the greater t h e reflection and consequent hiding power. A layer of white lead will reflect more light t h a n a layer of finely ground silica, since t h e refractive index of t h e lead is higher t h a n the refractive index of silica. When either of these pigments are ground in water, t h e same phenomenon holds true. b u t both arc less opaque t h a n in dry form because water has a higher refractive index than air. A s the refractive i n d e x o j the vehicle approaches that o j the p i g m e n t , opacity d i m i f t i s h e s , an optical condition being produced by t h e film around the particles, t h a t allows t h e passage of light, thus decreasing t h e reflection. When turpentine is used as a binding medium, t h e pigments show the same relative differences in hiding power, b u t both are less opaque t h a n when in water, since turpentine is more highly refractive t h a n water. When
