,
JANUARY, 1938
”
INDUSTRL41, AND EKGINEERIM$QCHEMISTRY
inch span of 61,/2 and 3 pounds for 3/’16- and l/‘s-inch tile, respectively. At break or pull-out, the deflection shall be not less than 0.4 inch. CURLING. The tile shall not curl more than 0.05 inch in 120 hours when laid on 8 moist flat slab of limestone. Curling and shrinkage are two defects with which manufacturers are particularly concerned. FLAMMABILITY. The tile shall not continue to flame for more than 30 seconds after exposure to a Bunsen burner flame for 15 seconds.
Acknowledgment The author wishes to acknowledge the cooperation of David E. Kennedy, Inc., in imparting information and granting permission to take plant photographs.
23
Literature Cited (1) Bonney, R . D., and Maguire, J. F. (to Congoleum-Nairn, Inc.), TJ. -~ S. Patent 1.985.201 (Dee. 18. 1934). (2) Claxton, E., and Bare, M. K. (to Armstrong Cork Co.), I h i d . . 2,022,707 (Dec. 3, 1935). (3) Ellis, Carleton, “Chemistry of Synthetic Resins,” p. 137, New York, Reinhold Publishing Corp., 1935. (4) Ellis. Carleton. U. S. Patents 1,676,604, 1,690,335 (1928); 1,814,135, 1,835,766, 1,835,767 (1931). (5) Federal Specification for Tile; Asphalt, SS-T-306. (6) Hannam, G. C., and Schede, J. W., U. S. Patent 1,637,301 (July 26, 1927). (7) Ibid., 1,637,302 (July 26, 1927). (8) Lukens, A. R., Ibid., 1,430,392 (Sept. 26, 1922). (9) McBurney, J. W., Proc. Am. SOC.Testing MateriaZs, 34, Pt. IT, 591-607 (1934). RECEIVED December 31, 1936.
Sanitary Value of Sodium Meta-
phosphate in Dishwashing Relative Value of Film Prevention and Auxiliary
Chemical Disinfection GEORGE 0. HALL Mellon Institute of Industrial Research, Pittsburgh, Pa. CHARLES SCHWARTZ Hall Laboratories, Pittsburgh, Pa.
N LARGE-SCALE as well as domestic cleaning processes, the character of the water supply is a factor of the utmost
I
importance in determining the efficiency of the cleaning operation. Unfortunately the most effective detergents, the soaps and the alkaline salts (phosphates, silicates, and carbonates) form extremely insoluble alkaline earth salts. As a consequence, when these agents are used in waters containing more than traces of calcium or magnesium, precipitation occurs; owing to their adherent character these insoluble compounds, especially the soaps, are deposited as films on the articles being washed and also on the washing equipment. These deposits are not only objectionable from the esthetic point of view, but they contribute to the difficulty of maintaining proper sanitation. The obvious solution of this difficulty would appear to be to soften the water supply. However, although the laundries and the textile mills recognize the necessity of soft water, the desirability of soft water has not been so apparent to the operator of dishwashing equipment. Reduced to its simplest terms, the softening of water consists in reducing the concentration of calcium and magnesium ions to the limit characteristic of the process employed. Although the conventional methods of water softening involve the physical removal of
A bacteriologic study is presented of the relative sanitational value of a film-preventing detergent, alone and in conjunction with an auxiliary germicide (sodium hypochlorite), and of detergents lacking specific film-preventing properties, alone and in conjunction with sodium hypochlorite. The results indicate that, although the use of sodium hypochlorite is definitely beneficial in conjunction with film-forming detergents, the presence of alkaline earth soap film prevents the realization of the complete effectiveness of this efficient germicide. The necessity for the use of an auxiliary germicide with a film-preventing detergent is shown to be questionable.
calcium and magnesium froin solution, either by precipitation or by base exchange, a third unique process does not require the physical removal of calcium and magnesium from solution, but only their conversion to a soluble but nonionized form. This process was termed “sequestration” by Hall
24
VOL. 30,NO. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
(5), its discoverer; it utilizes the unique property of sodium metaphosphate of forming, with calcium and magnesium ions, soluble complexes of such great stability that they respond to none of the common precipitation reagents for either metal. Even in alkaline solution the concentration of calcium and magnesium ion is reduced far below that necessary to satisfy the solubility product relations for the formation of any of their known insoluble (film-forming) salts. Sodium metaphosphate which is produced by the LLmolecular dehydration" of monosodium phosphate is easily soluble and is nontoxic. Its introduction as an ingredient of a n allialine detergent for machine dishwashing has enabled the complete prevention of the precipitation of the alkaline earth soaps and salts responsible for film formation. The prevention of film has been shown ( 2 , 6 )to produce a marked improvement in both the esthetic and the sanitaryqualityof machine-washed dishes. The results obtained in a sanitary investigation of the film-preventive function of sodium metaphosphate in an alkaline detergent for machine dishwashing emphasize the close correlation existing between physical cleanliness-i. e., freedom from visible soil or film-and cleanliness in the bacteriological sense. Although the sanitational value of alkaline detergents used in conjunction with a n abundance of hot water for the washing and rinsing of dishes is well recognized, the use of a n auxiliary germicide, usually a compound of chlorine, has been recommended (1, 6) where an adequate supply of hot water is not available. The present study was undertaken for the purpose of determining, from the sanitary standpoint, the relative effectiveness of a film-preventing detergent and of a detergent having film-forming properties used in conjunction with an auxiliary germicide (sodium hypochlorite). An investigation of this type should indicate, from a public health standpoint, the actual value of a n auxiliary germicide in compensating for the relatively high bacterial retention resulting from the film-forming properties of ordinary detergents. It should demonstrate further whether physical cleanliness as produced by the use of a film-preventive detergent was equivalent to the degree of cleanliness obtained by the use of a film-forming detergent supplemented by a n auxiliary germicide.
Experimental Procedure Petri dishes, 90 X 15 mm., were used in all of the washing operations. This simplified the matter of finding the number of bacteria on each dish. Furthermore, the slightest amount of filmwas also more easily detected on clear glass than on china. Fifteen- t o eighteen-hour whole milk cultures of Staphylococcus aureus were used in the tests. Milk is a natural medium for bacteria and also a common soil on dishes. It lends itself particularly well to these experiments, since it contains roughly 600 p. p. m. of calcium, which adds t o the hardness of the water. StaphyZococcus aureus was selected because it is probably most representative of those bacteria present on normally soiled dishes. It is also well adapted for this test because it coagulates milk. The bacteria are thus entrapped in the curd which, when dried, adheres firmly t o the glass. With a sterile pipet the milk culture w'as added t o clean, sterile Petri dishes in 5-ml. amounts. These were then dried in an incubator at 37.5" C. In order t o hasten evaporation, the lid of the dish was raised slightly at one side; from 36 t o 48 hours were necessary for evaporating the milk t o dryness.
stock solution of sodium hypochlorite was prepared daily from a commercial calcium hypochlorite, from which suitable quantities were added to the wash water to give the desired "available-chlorine" content. The temperature of the water was maintained between 130" and 140°F. The motor on the machine was stopped after the preliminary spray, while the detergent and the sodium hypochlorite solution were added. One dish was washed a t a time, and each was placed in exactly the same position in the machine. The washing solution was made up to a concentration of either 100 or 200 p. p. m. of available chlorine, as indicated. Melted agar was poured into each dish when it was taken from the machine and the lid replaced. The dishes were then incubated a t 37.5" C. for 48 hours, and the colonies counted. The results are presented in Table I.
TABLE I. DISHESWASHEDWITH DETERGENTS ALONEAND WITH HYPOCHLORITE IN THE W.4SHING SOLUTION No. of Dishes
Detergent
76 79 186 100 P . p . m. available C1 in wash: 0.2570 A
B C m. available C1 in wash: A
200 P.
99 47
4
9 29 22
2.5
17
2.5 6.5 0.5
34
B C
0.25
A v . No. of Colonies per Plate
25
6
1
Hypochlorite in Rinse Water Another set of dishes similarly soiled was washed in accordance with the preceding technic, but the germicide was not added to the wash water. Instead the dishes, after the final water rinse in the machine, were rinsed by hand in solutions of hypochlorite containing 50 or 100 p. p. m. of available chlorine for a period of 30 or of 60 seconds. Following this, the dishes were rinsed under the tap and poured with agar as previously described. The results of this procedure are shown in Table 11. TABLE 11. W.4SHED DISHES,R ISSED SOLUTION
IN
HYPOCHLORITE Av. No: of Colonies
Detergent
No. of Dishes
30-sec. rinse in 50 p. p. in. available CI: 0.25% A 0.250j, B 0.25% C
62 24 36
9.5 6.5 1.0
16 15 17
6.5 3.5 0.5
per Plate
._ 60-sec. rinse in 100 p. p.
111.
available C1:
Hypochlorite in Washing Solution The dishes were washed in the dishwashing machine already described, using a 30-second preliminary spray, a 3minute wash, and two 30-second rinses. The cleaners used were: A, a trisodium phosphate detergent; B, a dishwashing compound containing sodium pyrophosphate and sodium metasilicate; and C, a metaphosphatecontaining cleaner, of composition previously described. A
The results obtained with the dishes washed in the detergents alone (Table I) confirm the results previously obtained (2) which indicated the superior sanitary quality of dishes washed with a film-preventing detergent, C. The use of hypochlorite either in the washing solution or as a final rinse improved the results obtained with all of the detergents tested. However, the reduced counts in the dishes washed
INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY, 1938
,
100
counted after 48 hours. The results are presented in Table 111. I n the absence of definite standards and in order for the comparison between the detergents and procedures used in this work to be more readily visible, some of the data have been plotted so that the percentage of dishes with plate counts in excess of any given number may be read from a curve (Figure 1). Thus the number of colonies per plate are plotted as abscissas and the per cent of plates having colonies, in excess of any given number, as ordinates. I n Figure la, curve C, at point 10 on the abscissa axis the ordinate value is also 10, which indicates that 10 per cent of the C-washed dishes had more than 10 colonies per plate; any other value is found similarly. Thus, once a permissible maximum has been established, the number of dishes having more than this maximum for any given set of conditions may be read from a curve of this type.
I
1 80
,
25
il a I
TABLE 111. DISHESSCRAPED WITH STERILE INOCULATING NEEDLEWHILEPOCRING AGAR No. of Dishes 34 35 45 100 p. p. m. available C1 in wash 36 40 200 p. p. m. available C1 in wash 6 30-sec. rinse in 50 p. p. m. available CI 17 60-sec. rinse in 50 p. p. m. available C1 Detergent
02577 A 0:25$ B 0.25 C A A B 0.25% B
m €0
40
20
0
IO
20
30 40 50 60 10 N U M B E R OF C O L O N I E S / P L A T L
80
90
100
FIGURE 1. CURVESFOR READIXGTHE PERCENTAGE OF DISHESWITH PLATECOUNTSIN EXCESSOF ANY GIVEN NUMBER a. Dishes washed with detergents alone: no scraping. b. Dishes washed with detergents alone: scraped while plating. e . Dishes washed with detergent and 200 p. p. m. available chlorine in washing solution: no scraping. d . Comparison of various procedures.
in both detergents A and B with hypochlorite were not correlative with the physical cleanliness of the dishes, because a thin visible film remained on all of these dishes and small particles of unremoved soil remained on some of the dishes. The thought was thereby suggested that bacteria might be entrapped more deeply in the film, thus possibly escaping the germicidal action of the hypochlorite solution. Accordingly another set of dishes was soiled, using 5 ml. of inoculated milk. They were then washed as before with the materials indicated in Table 11. I n these dishes, however, before the melted agar had solidified, the film was scraped with a sterile inoculating needle in order to expose any bacteria which may have otherwise been protected under the film. The plates were then incubated and the colonies
+ + ++
Av. No: of Colonies per Plate 320 206 2.5 37 7 29 25
The inferences which may be drawn from these results are significant. Considering first the counts obtained after scratching the dishes washed with the detergents alone, it is apparent that the films on the dishes washed with detergents A and B have retained relatively large numbers of bacteria (Figure 16). It is further apparent that the dishes washed with C, which were virtually free from film, were also virtually free from bacteria. To recapitulate, the presence of ?odium metaphosphate in detergent C by preventing the deposition of sticky alkaline earth soaps has so facilitated the rinsing of the dishes that the bacteria initially present have been largely removed by the dilution effect of the rinse water. On the other hand, the dishes washed with detergents A and B, lacking specific am-preventing properties, have retained more bacteria because they have been trapped by the insoluble film of alkaline earth soaps. Consequently they have resisted removal by the dilution effect of the rinse mater. The results obtained after scratching the dishes washed with detergents A and B in conjunction with sodium hypochlorite, both in the wash and in the rinse, are likewise of interest. The marked increase in the number of colonies shown by comparing corresponding values in Table 111and Tables I and I1 is indicative that the hypochlorite has effected only a sterilization of the surface of the plates and that the bacteria harbored beneath the film have been protected from the action of the germicide. It is apparent from a consideration of the results here presented that, if the different combinations of treatment are to be rated on a basis of their sanitary efficiency, their order mould be ( a ) a film-preventing detergent m-ith hypochlorite, (6) a film-preventing detergent alone, ( c ) a film-forming detergent with hypochlorite, ( d ) a film-forming detergent alone.
Discussion of Results I n the absence of established standards for the permissible number of colonies per unit area of washed dish, it is rather difficult to appraise the actual necessity for the use of an aux-
26
INDUSTRIAL AND ENGINEERING CHEMISTRY
iliary germicide in machine dishwashing. Undoubtedly the degree of sterilization effected by a chlorine rinse of a film-free washed dish would approach the ultimate obtainable in practice, especially in view of the statement of Mailman ( 6 ) that the production of absolute sterilization is impractical. Even though liberal interpretation of the data could be construed to indicate equality between the sanitary results for a filmforming detergent used with an auxiliary germicide and the results for a film-preventing detergent alone, the former treatment would leave much to he desired both on esthetic and on sanitary grounds. In the first plaee, the presence of film on eating utensils is unsightly and unappetizing, whereas the dishes washed with a film-preventing detergent present an unusually attractivc appearance because of the absence of 6lm. Furthermore, in view of the data presented here and elsewhere @), this physical cleanliness is also indicative of cleanliness in the sanitary sense. In the second place, it has been shown that the sterilization effected by film-forming d o tergents in conjunction with sodium hypochlnrite is more a p parent than real; it is only skin deep, so to speak. It is by no means an exaggeration to assume that, under actual conditions, t,he knife, fork, and spoon may simulate the action of the needle, especially in eating places where film has been pennitted to accumulate on the dishes. The question as to whether i t is necessary to submit dishes that have been washed with a film-preventing detergent to treatment with an auxiliary germicide is left open, but there are some practical points involved in this procedure, apart from aanitary considerations, that merit attention. Dishwashing machines now available are not equipped to use auxiliary germicides. If the agent to be used is a compound of chlorine, some type of dispensing mechanism is essential in order to maintain continuously an effective chlorine concentration. Although a dispenser could undoubtedly be contrived which could compensate for ordinary dilution, the dispensing problem is further complicated by the organic matter which, when present in quantity, markedly reduces the efficiency of chlorine and its compounds (4). Under the conditions, hand dispensing is hardly feasible. The requirement of an afterrinse in hypochlorite outside of the machine nullifies to a large extent the economy of mechanical equipment, hecause machines are used primarily to reduce handling and to expedite
VOL. 30, NO. 1
the dishwashing process. Although the question of expense should not take precedence in questions of public health, i t would appear that any method of sanitation requiring extensive and costly changes in equipment or increased uperating time would he relatively slow of adoption.
Summary Earlier work demonstrating the sanitational value of the film-preventing property of sodium metaphosphate in machine dishwashing has been confirmed and extended. The relatively high bacterial retention by dishes washed with detergents lacking specific film-preventing properties is caused by the presence of insoluble alkaline earth soap film which protects entrapped bacteria from the diluting action of the rinse water. In a similar manner, the sterilization effected by the use of sodium hypochloritein conjunction with analkaline detergent lacking specific film-preventing properties is confined to the surface because the presence of alkaline earth soap film protects underlying bacteria from the action of the germicide. Under the circumstances the most efficient method of using sodium hypochlorite as an auxiliary germicide would be in conjunction with a film-preventing detergent. The necessity for the use of an auxiliary germicide in conjunction with an alkaline dishwashing detergent having specific film-preventing propcrties is open to question, in view of the fact that the sanitary results obtained from the use of the detergent alone are a t least equal to the results obtained from the combination of a film-forming detergent and an auxiliary germicide.
Literature Cited (1) Cumming, J. G., and Yongue, N. E., Am, I.Pub. Health, 26, 237 (1936). (2) Hall. G. 0.. and Schwartz, Charles. IND.ENG.CHEM., 29, 421
~~"~.,. 1,097,
(3) Hall, R. E., U. S. Patent 1,956,515 (Awil24. 1934). (4) MoCulloch, E. C.. "Disinfection and Steriliestion,"
p. 394, Philadelphia, Lea and Febigrr. 1936. ( 5 ) Mallman, W. I,., A n . I.Pub. Health, 27,464 (1937). (6) Schwartz. C., and Gilrrrore, B. H., IND. ENO.Cnnar., 26, QQS (1934). R~CEIYEI) Auguat 4. 1837. Contribution from the Csieoniaing Fellorahin a t the Mellon Inntitate of lndaatrial Research.
ATMoSPKEnIc DEUMDRYER UsEn BY E. I. DO PONT DE N E M ~ U&RCOMPANY ~ AT TRE DEEPWATEX
POINT,N. J., PLNT
COyTlC*Y,
dU Pant cornpony
