J. Sac. Cosmetic Chemists, 17, 5391551 (1966)
`
`The Practical Evaluation of
`
`Shampoos
`
`lWARSHALL SORKIN, M.S., BERTRAM SHAPIRO, BS, and
`GUS S. KASS, B.S.*
`
`Presented December 1, 1965, New York City
`
`Synopsis#Appearance, performance during use, and effect on hair after use are the three
`major criteria by which shampoos should be evaluated. Within these three broad categories,
`25 separate characteristics are enumerated. The importance of each of these and laboratory
`and beauty salon test procedures for evaluating shampoos are discussed.
`
`INTRoDUCTnJN
`
`The development of a shampoo that can win a significant share of a
`highly competitive market is not a simple task. Even though a shampoo
`is more or less a rather prosaic toiletry, many of its qualities, or lack of
`these qualities, can affect the consumer either favorably or adversely.
`The chances of developing a utility shampoo with a significant innova-
`tion are rather remote. The term utility shampoo is used to differenti-
`ate between the general use shampoo and those which are more specific-
`ally defined, suCh as antidandruff shampoos, color shampoos, etc.
`In
`order to produce a successful shampoo of the utility type, it must have a
`quality of excellence built into it. This quality of excellence is almost
`always a total combination of many factors, some of which are im—
`mediately obvious to the consumer and many of which are not.
`The consumer reacts to a shampoo at three different times. The
`consumer will be considered to be female, since almost all of the general
`use family shampoo is purchased by a feminine member of the family.
`
`
`* Alberto—Culver Company, Melrose Park, Ill.
`539
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` 41R AIXH R T 1047
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`UN THIV
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`UN Tali/41R VS. PROCTOR & GAMBLE
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`IPR20l3-00509
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`UNILEVER EXHIBIT 1047
`UNILEVER VS. PROCTOR & GAMBLE
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`It is true that her decision is influenced by advertising, packaging, brand
`name, and reputation of the manufacturer—and, perhaps a great deal
`more than one would like to admit, by price. Her first real impressions
`are established when she picks the package off the shelf.
`If she is
`favorably impressed at that time she may buy and use the shampoo.
`Her decision whether to purchase the product again is influenced twice
`more. How did the shampoo perform, and how did it leave her hair?
`Most discussions of shampoo performance found in the literature are
`limited to evaluation of foaming qualities, manageability, and deter—
`gency. There are many other factors that contribute to a quality
`shampoo, which have been delineated in 25 distinct categories. Every
`shampoo under development and all competitive shampoos are evalu—
`ated against this check list. Many of the qualities can be measured by
`well—established laboratory procedures. Others must be evaluated by
`specially devised techniques. And still other qualities can only be
`determined subjectively, and here experience and a thorough understand-
`ing of shampoos are invaluable.
`Details of the formulation or composition of shampoos will not be
`considered.
`Instead, the major objective is a discussion of the practical
`evaluation of the 25 characteristics or qualities which enable the chemist
`to determine whether or not a shampoo has that certain “quality of excel—
`lence,” as measured by the consumer. These qualities are reviewed
`not necessarily in order of importance; nor are they studied in the order
`shown; and many of them are interrelated.
`The methods of evaluation as described in this paper apply to a clear
`liquid shampoo although similar criteria may be applied to a liquid
`lotion or a cream shampoo.
`The 25 shampoo qualities can be divided into three broad groups.
`This is primarily a check list designed for the fairly rapid evaluation of
`large numbers of shampoos on a routine basis. The first group concerns
`the appearance of the product itself in the bottle and includes the. fol—
`lowing nine qualities for evaluation:
`
`1 . Clarity
`
`2. Viscosity
`3 . Color
`
`4. Color stability
`
`5. Cloud point
`
`71¢
`
`Clear point
`
`pH
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`PRACTICAL E VA 1, UA’l‘l ON 01“ SHAlVll’OOS
`
`54 1
`
`8. Fragrance
`9. Sterility
`
`The second group of qualities relates to or is directly concerned
`with the actual performance 011 the hair and includes:
`
`10. Foam productioniehard water
`11. Foam productioni-soft water
`12. Foam production—hard water plus soil
`13. Foam stability
`14. Foam texture
`
`15. Speed of foam production
`1 6. Rinseability
`17. Fragrance 0f lather
`
`The third group of characteristics concerns the effect of the shampoo
`on both the hair and skin.
`‘Here the following qualities are evaluated:
`
`18. Combability of wet hair
`19. Combability of dry hair
`20. Static electricity of the hair
`2]. Fragrance of the hair
`22. Hair gloss
`23. Effect on artificial hair color
`
`24. Staining of bleached or permanent waved hair
`25. Feel on hands
`
`SHAMPOO EVALUATION
`
`Clam'ty
`
`From a consumer point of view, the general outward appearance of
`the shampoo is the first contact with the product itself, stripped of its
`outer covering of label and package. For this reason it is most impor—
`tant that a clear shampoo be manufactured with maximum care. A
`shampoo with sparkling clarity has obviously greater consumer appeal
`that one that is hazy.
`The danger in formulating clear shampoos is loss of clarity with
`aging, a fairly common defect. Only thorough stability testing of the
`shampoo will reveal this problem so that measures can be taken to solve
`it. Among the factors contributing to loss of clarity are temperature,
`perfume, water hardness, contamination by microorganisms, and water—
`insoluble fatty compounds used as hair conditioning agents.
`Cloud point and clear point. evaluations are important in order to
`maintain clarity under a range of colder—than—normal temperatures.
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`The cloud point is the highest temperature at which the shampoo will
`cloud or haze when cooled. The clear point is the lowest temperature
`at which the product will clear when warmed from a chilled opaque
`condition. They are not always the same. Clarity, insofar as cloud
`and clear points are concerned, should be maintained at about a maximum
`of 10°C. This should insure clarity in stores and homes under average
`conditions of temperature.
`
`Viscosity
`
`Liquid shampoos comprise the largest share of the shampoo market,
`with clear liquid shampoos accounting for better than 50% of the market.
`Among the most important characteristics of these products is viscosity
`which may range from water—thin products to viscous liquids. There
`are both psychological and practical advantages to relatively high Vis—
`cosity liquid shampoos. They often imply a high concentration of
`shampoo ingredients plus a richness that is usually associated with
`hair conditioning and management. There is also a practical value.
`High viscosity liquid shampoos can be poured into the palm of the hand
`for application to the hair, thus eliminating dripping through the fingers
`or down the face and neck.
`
`A desirable viscosity range will vary between 500 and 1500 cps.
`Shampoos having viscosities below this level tend to be runny; and if the
`viscosity is over 2000 cps, they may not pour too well. Maintaining
`viscosity within a close range over a long period of time can some—
`times be a problem. Here again, stability testing is of utmost
`ime
`portance.
`
`Color
`
`A shampoo may be uncolored, or it may have certified color added.
`Thc color of a shampoo is dictated by esthetic considerations, packag—
`ing, and subtle psychological factors. The market
`to which it
`is
`directed is also a factor. A shampoo for men may be blue, green, amber,
`or gold, or it may be colorless, but pink would be a doubtful choice.
`There has been a transition over the years in the colors which the con-
`sumer prefers. Until recent years liquid shampoos were usually amber,
`yellow, or orange. More recently, green and blue shampoos have
`become popular. Clear, colorless shampoos are also on the market.
`Such shades as lavender and red and deep colors are particularly un—
`acceptable.
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`PRACTICAL EVALUATION OF SHAMPOOS
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`543
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`(Mar Stability
`
`In selecting the color to be used, color stability or instability can
`become a problem. Many of the certified dyes used are sensitive to
`
`It should be unnecessary to
`light, pH, and other chemical factors.
`state that every shampoo should be thoroughly tested for light stability.
`Since it is not always convenient to set the product in the sun and since
`the results are not reproducible, a commercial “fadeometer” may be
`used to determine color stability.
`In such equipment the shampoo is
`exposed to high intensity ultraviolet light under controlled conditions.
`A minimum exposure of six hours with negligible or no color change is
`usually considered acceptable.
`Incidentally, one of the pitfalls to be avoided in light exposure studies
`is to test the shampoo in a container made from the same material as the
`ultimate package.
`It is not unusual to find a color that may fade in
`glass but is stable in a given plastic and vice versa. With the de—listing
`of many certified colors, the problem of finding a suitable color that is
`stable to light has increased. The use of ultraviolet absorbents in the
`
`shampoo can be extremely helpful in improving the light stability of
`fugitive colors. Some container manufacturers are coating their glass
`or plastic bottles with ultraviolet absorbents which serve the same pur-
`pose.
`
`A third area where the color of a shampoo should be evaluated is
`one that is frequently overlooked. Some hair, and this is especially
`true of bleached and permanently waved hair, is quite porous and may
`absorb the color from the shampoo. Here again, pH and chemical
`composition of the product may be contributing factors. Only thorough
`testing on laboratory hair swatches and subsequent application to sub—
`jects with bleached or permanently waved hair will determine whether
`this problem exists.
`
`pH
`
`The pH of a shampoo may have definite effects upon its properties.
`Most liquid shampoos today are formulated to have a pH between 6.5
`and 8.5. Within this range a suitable viscosity and clarity can usually
`be achieved, as well as good stability and lathering properties. A few
`generalizations can be made concerning the effects of pH on a typical
`clear shampoo formulation:
`
`1. Shampoos formulated on the high side of the pH range will
`exhibit a greater degree of foaming and cleansing as well as a
`greater ability to strip the natural oils from the hair.
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`4.
`0’!
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`2. Conversely, shampoos 011 the low side of the range will generally
`leave the hair in better condition with a greater degree of man-
`ageability and combability.
`3. Shampoos with pH’s above and beyond the high sidc of the range
`can cause eye irritation more readily than those within the range.
`It is easier to maintain clarity on the high side of the pH range.
`Viscosity generally increases as the pH is lowered. This is
`especially true of alkylolamide—lauryl sulfate shampoos.
`pH can, therefore, be considered as a key factor in formulating a
`product to suit the consumer’s desires. Although she may never have
`heard of the term, pH can affect the appearance, efficacy, and residual
`performance of a shampoo.
`
`Fragrance
`
`It can
`The fragrance of a shampoo is a most important quality.
`add a touch of cosmetic elegance to the product plus an air of distinc—
`tion.
`It can significantly influence the consumer whether or not to
`purchase the product initially or to repurchase it.
`It is the authors’
`opinion that a shampoo fragrance should be a light and clean bouquet;
`but the perfume type will be dictated by whether the shampoo is mar—
`keted primarily to women, men, children, or for family use.
`The shampoo fragrance should be evaluated critically at three dif-
`ferent stages. First,
`the product itself in the bottle. A buyer will
`often remove the cap and sniff the product at the shelf or counter. Does
`it have a light refreshing scent with high appeal?
`Is the shampoo free
`of a chemical or detergent odor;
`is it effectively masked? Does the
`fragrance appeal to the consumer group to whom the shampoo is di-
`rected? The fragrance at point of purchase can often make or prevent
`a sale.
`
`The second time that the fragrance may elicit a response from the
`consumer is during application to the hair. The use of hot water plus
`the fact that shampoos are often applied to the hair in a confined area,
`such as the bathroom or shower, can result in a fragrance change notice-
`able in the lather and in the atmosphere. The fragrance should retain
`its basic characteristics without becoming overpowering.
`The third important stage is the fragrance of the hair after shampoo-
`ing. The hair should retain an almost imperceptible scent. Certain
`perfume types should be avoided, such as heavy, sweet types which tend
`to cling to the hair. Hair that has been bleached or permanently waved
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`PRACTHCAL EVALUAJWON OF SHALJPOOS
`
`545
`
`tends to retain more of the fragrance than chemically untreated hair.
`
`Also, hair that has been shampooed with products containing amphoteric
`surfactants often retains more fragrance than when anionic surfactants
`are used.
`
`Sterility
`
`For some reason cosmetic chemists often disregard or minimize the
`potential problem of shampoo contamination by microorganisms. They
`would not consider marketing a cream or lotion that is inadequately
`preserved, but shampoos are often found without preservatives. There
`is a mistaken notion that, since sulfated lauryl alcohol and sulfated
`ethers are considered antagonistic to bacterial and fungal growth, no
`contamination problems exist
`in shampoos. Several
`investigators
`(1, 2) have sh0wn that this is only partly true, and shampoos are often
`found that give high bacterial counts—particularly of gram—negative
`bacteria. This has been confirmed by the authors’ experience over the
`years. Contamination by microorganisms poses not only a health
`hazard but can cause changes in the shampoo, such as malodor, tur-
`bidity, and viSCosity changes. On the other hand, it is also possible to
`find grossly contaminated products without visible signs of change.
`All shampoos must be preserved not only for original freedom from
`contamination but also must be protected against the possibility of
`future contamination when the package is opened and reopened for use.
`Many preservatives are available for use in shampoos today, and their
`incorporation is fairly simple; h0wever, their effect on certain organisms
`may either diminish in time or cause the generation of resistant strains.
`Thus, even after many years of preservation by specific agents have passed
`safely, a periodic investigation should be undertaken to determine
`whether the preservatives are still effective. Freedom from micro—
`organisms not only depends on adequate preservation but also upon
`uncontaminated raw materials—particularly water. Vitally essential
`are strict sanitary measures during manufacture. Constant diligence
`is required, and development production shampoos should be routinely
`subjected to bacteriological evaluation.
`
`Foaming
`
`To the consumer, foaming or lathering action is one of the most
`important aspects in determining the quality of a shampoo, and the
`measurement of foam has received much attention in the literature. The
`
`volume, foam structure, foam viscosity, and foam stability are also
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`important criteria by which the consumer judges the shampoo even
`though she may not realize it. Undoubtedly, techniques to measure
`and evaluate foaming qualities are important. Normally, such measure—
`ments are first performed in the laboratory and then in actual use on
`
`models. There have been many laboratory techniques developed over
`the years to measure foam, some of them highly sophisticated. The
`authors use a very simple technique which requires only a 500 ml glass
`stoppered cylinder and a device to revolve or agitate it. This very
`simple method has been widely criticized, and there are more precise
`procedures (3—5). For practical purposes and after thousands of foam
`
`mu
`
`5m
`
`4m
`
`vmw:nrmmm“,
`
`I
`/
`
`x
`
`
`———— SOFT HATER
`___ my mm) wan mm on.
`van mm mm mom»
`
`3m ”C
` _fi—v—fi——-——‘
`
`u
`
`VOLUM‘L or 1qu swoo sumeN \mH
`
`l u
`
`Figure 1. Foam curves of a commercial shampoo (Shampoo A)
`
`tests, this technique has been found to meet the following conditions:
`It is fast, it is reproducible, and it reflects the performance of the sham-
`poo on the hair.
`First, 10% dilutions of the shampoo in either soft water or water of
`known hardness are prepared.
`Increasing increments of the diluted
`shampoo are pipetted into the cylinder, diluted with water of required
`hardness to a fixed level, and then rotated for a precise number of times.
`The foam volume is recorded, and the bubble structure and foam sta—
`
`bility are examined. Three foam curves are plotted for every shampoo:
`A soft water dilution; a dilution with water of known hardness; and
`a dilution of water with known hardness plus the addition of 1 ml of
`olive oil. The foam determination in the presence of oil fairly accurately
`
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`PRACTICAL EVALUATION OF SHAMPOOS
`
`547
`
`reflects the performance of the shampoo on the first lathering. Dur-
`ing the first lathering the foam is often depressed because of sebum,
`hair dressings, and other cosmetic products which may be on the hair.
`The hard and soft water curves represent the range of water hardness
`used by consumers throughout the country and can be a major factor
`in the type of foam developed. Figure 1 illustrates these three foam
`curves of a nationally advertised brand of shampoo. Figure 2 shows
`the foam curves in very hard water (310 ppm.) of two popular sham—
`poos. This significant difference in foam production of shampoos
`A and B is also evident when the two shampoos are actually applied to
`the hair of a subject using a “half—head” technique.
`mo
`
`500
`
`um)
`
`JED
`
`Luann/r:nryou(m1)
`
`zoo
`
`ion
`
`»7__ smuruo "A"
`smnpno "l"
`
`
`
`a
`mum»: up m7, sxmoo suunm (ml)
`
`Figure 2. Comparison of the. foam volume of two shampoos in
`very hard water (310 ppm)
`
`The most important test in evaluating shampoo performance is to
`shampoo a variety of hair types under controlled conditions and observe
`the results. The recommended method is the “half—head” technique
`which involves parting the hair down the center and shampooing each
`half simultaneously with two different shampoos. The “half—head”
`technique is commonly used with many hair preparations such as hair
`sprays, wave sets, hair dressings, etc. With these, “half-head” testing
`is simple and easy, but it is not quite so simple with a shampoo.
`The reasons for “half—head” testing are quite obvious. No two
`heads of hair are the same. The hair varies in texture, length, condition,
`sebum and soil content, and presence of cosmetics. Therefore, compar—
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`ing Shampoo A on one head with Shampoo B on another head is rather
`meaningless, especially if only subtle differences exist. One must then
`rely on memory and, therefore, cannot compare the results of a head
`shampooed with product A and subsequently treated with shampoo B.
`A skilled beautician can apply two shampoos to the same head and, if
`done on a number of heads, obtain meaningful and reproducible results.
`Two shampoos are applied to dampened hair in equal amounts
`(from glass hypodermic syringes for accuracy and convenience)
`to
`both sides. The lather is worked up as uniformly as possible on both
`sides of the head and the various lathering and foaming qualities ob—
`served, including the speed at which the lather develops, the so-called
`“flash-foam” characteristics. A second lather is worked up, again using
`
`syringes for accurate dispensing of the shampoo, and the evaluation is
`repeated. Very often the second lather is allowed to remain on the
`hair for three to five minutes and foam collapse, if any, noted. The
`shampoos are rinsed from the hair and the rinsing characteristics ob-
`served.
`It has been found that some shampoos rinse very rapidly
`while others continue to produce foam for several minutes during the
`rinsing procedure.
`The foam texture is also examined during these tests. Foam made
`up of large, thin bubbles is not desirable; neither is foam made up of
`very small bubbles, which tend to make the foam feel like a cream.
`Incidentally, one observation made during these “half—head” tests is
`frequently overlooked. How does the shampoo feel on the hands during
`application? Does the shampoo impart
`the desirable soap—like lu-
`bricity, or does it impart a raspy harsh feel to the hands? The consumer
`has been conditioned to the feeling of lubricity or slip that is always
`characteristic of soap and most shampoos. With the current trend to
`shampoos of lower pH, this quality can be lost. A shampoo of pH
`6.0 to 6.5 can lack this feeling of lubricity on the hands, but the problem
`can be resolved by skillful formulation.
`
`11!(mageability
`
`Perhaps one of the most abused words used in shampoo advertising
`is “manageability" or “conditioning." Such claims are frequently
`made for shampoos, even though they do not exist. However, they are
`meaningful to the consumer and are, therefore, important to the chem—
`ist.
`Just what do these words mean? A healthy, normal head of hair
`is one that is easily combed when either wet or dry. This is due to
`natural secretions which coat the hair with a lubricating film, eliminate
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`Date
`
`Short
`Tinted
`
`Dry
`Fine
`Good
`
`CLINIC SHAMPOO TEST
`
`Subject —_— Ph.
`
`DESCRIPTION OF HA IR
`
`Medium
`Bleached
`
`Nurmal
`Medium
`Fair
`
`Date
`
`PM.
`
`Long
`
`Oily
`Coarse
`Poor
`
`Date of Last Shampoo
`
`Shampno Used
`
`HE
`
`E
`
`Shampoo Used
`Dilution
`Amount
`
`lat
`
`2nd
`lat
`
`2nd
`lat.
`
`2nd
`
`Slaw
`
`Av.
`
`Fast
`
`Foaming
`
`Little
`
`Av.
`
`Heavy
`
`Volume
`
`Thin
`
`Av.
`
`Thick
`
`Density
`
`lst
`
`2nd
`lst
`
`2nd
`lst
`
`2nd
`
`Slaw
`
`Av.
`
`Fast
`
`Little
`
`Av.
`
`Heavy
`
`Thin
`
`Av.
`
`Thick
`
`Collanse
`Hinsability
`Feel-Wet
`Combability—Web
`Feel~Dry
`Cumbability-Dry
`Static Charge
`Body
`Sheen
`
`S
`h
`3
`'2
`l
`0
`5
`1 273 b
`o
`0123h5
`o
`1
`2
`3
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`1
`2
`3
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`2
`3
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`Other C manta
`Call Back Comments
`Date
`
`5
`h
`3
`2
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`
`Figure 3. Beauty Clinic form
`
`static charges, and impart gloss or sheen. Many shampoos will com—
`pletely strip the hair of sebum and other natural secretions, with the
`result that the wet hair snarls or tangles and is difficult to comb. The
`dry hair is often lustreless and also diflicult to comb. A strong static
`charge results in “fly-away” or hair difficult to hold in place.
`There are two solutions to this problem. One is to formulate a
`shampoo with reduced detergency. The shampoo will remove surface
`soil on the hair and most‘but not all eof the sebum coating. The
`amount of natural oils remaining on the hair is sufficient to impart some
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`‘ degree of “manageability.” A second solution is to compound a sham—
`poo that will cleanse the hair but still leave a film on it to serve tempor—
`arily as a conditioning agent until natural scalp secretions are replaced.
`The authors doubt that most so-called “conditioning agents” incorpor—
`ated in shampoos are deposited on the hair. There are, however, sub—
`stantive materials which are useful for this purpose.
`After the hair has been thoroughly rinsed and towel dried, it is again
`parted down the center and combed (using two identical clean combs)
`by both the beautician and the chemist, and differences in combability
`are noted. No other cosmetic products are used on the hair when
`shampoos are evaluated. When dry, the hair is again checked for dry
`combability, gloss, and static charge. Excellent methods have been
`devised for the measurement of static charge on hair (6, 7) but for rou—
`tine purposes visual observation is suflicient. All beauty clinic observa—
`tions are recorded on the form shown in Fig. 3. A subjective rating
`system is used whereby many of the characteristics discussed above are
`scored from U to 5, with 0 being very poor and 5 very good.
`In a series
`of tests on a shampoo, using suitable controls, meaningful observations
`are readily made as to the performance characteristics.
`
`Efiect 0f Shampoo on Hair Color
`
`In View of the tremendous growth of hair coloring, the possible effects
`of shampoos on artificially colored hair cannot be ignored. Specialty
`shampoos have been developed for use on color treated hair, but utility
`shampoos should also be checked. This is routinely performed in the
`laboratory and in the beauty clinic on hair that has been colored with
`oxidation dyes and with semi-permanent dyes.
`In the laboratory,
`the AAT CC Launderometer as modified by Goldemberg (10) is used.
`Observations of loss of color during shampooing and of color changes
`are made. Here again the “half—head” technique is useful because color
`changes and attrition of color may be due primarily to the color and not
`to the shampoo.
`
`CONCLUDING COMMENTS
`
`There are additional shampoo qualities that require evaluation, and
`omission of these from the list of 25 characteristics does not necessarily
`minimize their importance. Safety to the consumer is of paramount
`importance, and certainly no shampoo should ever be marketed that is a
`sensitizer or an irritant to the eyes or skin. Factors that contribute to
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`PRACTICAL EVALUATION OF SHAlVlPOOS
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`C71
`5 1
`
`such hazards are well known, and methods to detect them are in wide—
`
`spread use.
`Detergency has not been listed as an important consideration for
`routine evaluation. Although excellent methods have been reported
`for the measurement of detergency (8, 9), some cosmetic chemists are
`of the opinion that a shampoo should not be so powerful a detergent as
`to strip all natural secretions from the hair and scalp. Modern sham—
`poos are based on surface—active agents that perform this task adequately
`for all practical purposes. The latitude for degree of detergency is
`fairly wide. When one considers that most heads of hair are shampooed
`with two applications of shampoo,
`the factor of detergency becomes
`relatively unimportant.
`
`(Received November 24, 1965)
`
`REFERENCES
`
`(1) Bryce, D. M., and Smart, R., J. Soc. Cosmetic Chemists, 16, 187 (1965).
`(2) Schwartz, A. M., Perry, I. W., and Berch, ]., Surface Active Agents and Detergents 1]
`(1958), [nterscience Publishers, Inc., N. Y. (1958).
`(3) Myddlcton, Wm. W., J. Soc. Cosmetic Chemists, 4, 150 (1953).
`(4) Bromley, I. M., Ibid., 15, 631 (1964).
`(5) New, G. E., Proceedings of the Second Congrexs of the International Federation of Sactettes
`of Cosmetic Chemists, London, 1962. Edited by A. W. Middleton, The Macmillan Com,
`pany, New York (1963).
`(6) Mills, C. M., Ester, V. C., and Henkin, H., J. Soc. Casmetic Chemists, 7, 466 (1956).
`(7) Barber, R. (3., and Posner, A. M., Ibid., 10, 236 (1959).
`(8) Barnett, G., and Powers, D. 11., 1613., 2, 219 (1951).
`(9) Ervin, J. C., 11nd,, 3, 81 (1952).
`(10) Goldemberg, R. L., Ibid., 10, 291 (1959).
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