Soap Bubbles, Chapter 8

          The class just knew something interesting was coming when they found the big table full of soaps in all kinds of packages.
          Later, Miss Dean asked everybody to come to the table, take a package, and read the label on it.
          They had great fun finding out how many different things the labels said.
          Some labels talked about washing wool, silk, and other fine fabrics in the right way.
          Some said the soap contained “no silicate.”
          Some said the product made no suds. (“How can it be a soap, them?” asked John.)
          Some promised to blue the clothes, and others to bleach them.
          Some spoke about being good water softeners. And so on.
          ”I guess we haven’t learned all about soaps yet,” said Peter. “I’d like to know what all this means.”
          ”I want to know why some of these bars are yellow and some white,” said Grace.
          ”And I’ve just got to know why some soaps float,” said George.
          ”You make me think of a great big question mark,” laughed Miss Dean. “I see that we shall have to find out what is in these soaps to make them do what they claim to do.”
          ”Here is one which says it will soften hard water. After hearing Jimmy tell us about hard water, what would you think this soap might contain?”
          ”Washing soda,” was the general chorus.
          ”What is its other name?” asked Miss Dean.
          ”Sodium carbonate.”
          ”How do you boys who have chemical sets test for a carbonate?”
          ”Use acid,” said George, “and if there is a lot of fizzing, a carbonate is present. May I try it, please?” And he brought his chemical set to the table.
          ”Here is some sodium carbonate solution in this glass,” said George, as he prepared to make the test. “And now I am adding some acetic acid.”
          ”Wow! See it fizz!” said Peter. “It looks like soda water.”
          ”It certainly is soda water,” said Miss Dean, “although not exactly the kind you drink. The kind you drink is called soda water because it is made to fizz with the same gas that is fizzing here. Does anyone know the name of the gas?”
          ”Carbon dioxide,” said George. “It is given off when an acid is put on a carbonate.”
          ”Could we not test these soaps for sodium carbonate by putting an acid on them?” asked Jimmy.
          ”Easily,” said Miss Dean. “Here are some saucers, one for each package of soap. Put a little soap in each saucer, and stand the package behind it, so that we can keep track of the soap we are testing. If we were doing this at home, what acid might we use?”
          ”Vinegar?” asked Peggy.
          ”That’s what I was going to say,” said George, “because the acid I used, acetic, is in vinegar.”
          Meanwhile the soaps were put in the saucers, the bar soaps being scraped to get some flakes, which would test more easily. Miss Dean brought out a bottle of vinegar and it went from hand to hand, each soap being tested in turn.
          There was a shout whenever a soap fizzed. Some did not fizz at all, some fizzed a little, and some - these were the soap powders - fizzed up to the top of the saucer. Miss Dean explained that these were expected to contain washing soda and were not really soaps, but a soap and washing soda mixture.
          Some of the soaps tested had their names written on the board under the heading “Contains Washing Soda.”
          As we test for the substances that are added to the soap in these packages,” said Miss Dean, “let us find that substance in this row of bottles.” And she pointed to a row of bottles at the back of the table, with a sign above them: BUILDERS.
          ”That’s right,” said Peter. “I remember that the guide in the soap factory said that some things were added to soaps, and were called ‘builders,’ Here is the sodium carbonate, in this bottle. So that is a builder.”
          ”What does ‘builder’ mean, in soap?” asked Mary.
          ”Who can explain that?” asked Miss Dean, in her turn.
          ”I think,” said Jimmy, “that a builder must build up the soap to do something more than might be done without it, such as softening water.”
          ”That explains a builder pretty well,” said Miss Dean. “And washing soda in a soap softens hard water and helps the soap solution to cleanse.
          ”Grace asked, a while ago, why some bar soaps were yellow and some were white,” Miss Dean went on. “Do you see anything in this row of builders which might give a yellow color to soap?”
          ”Yes, Miss Dean,” said several children, “here is something called rosin.”
          ”That is it,” said Miss Dean.
          ”But what is rosin and why is it used?” asked a half dozen “question marks.”
          ”Rosin, sometimes called resin, comes from the pine tree,” said Miss Dean. “Down in the pine forests through the Carolinas and Georgia a certain kind of pine tree is tapped for its sap, just as sugar maple trees are tapped for their sugar sap. Turpentine is made from this sap and what is left is this gummy substance called rosin.
          ”Rosin combines with caustic soda just about as fat does, to make a rosin soap. Rosin soap is a deep yellow or brown. When it is mixed in a kettle with a soap from fats, the whole mass is colored yellow.”
          ”Is a rosin soap a good soap?” asked Gertrude.
          ”Yes, in some ways,” answered Miss Dean. “Rosin soaps make a good suds, and dissolve easily in cold water. But one reason for putting rosin in soap is that it saves fat, and fat costs more than rosin. The use of it has allowed the soap manufacturer to make a useful laundry soap to sell at a very low price.”
          ”Then, if they stop using rosin, will soaps cost more?” asked Peter.
          ”Pure soap, made of fats alone, will always cost more than if some cheaper builder is added,” said Miss Dean, “but we have the white laundry soaps, which sell for about the same price as the yellow. They do not contain rosin.”
          ”Then they must contain some other builder,” said George.
          ”They do,” said Miss Dean, “but you couldn’t possibly guess what it is.” And she pointed to a bottle containing a liquid which looked a little like water, but was thick and heavy, like syrup. The label said SODIUM SILICATE, or water glass.
          ”Why,” said Mary. “Mother uses water glass. She buys fresh eggs and puts them in water glass to keep them fresh.”
          ”Many people do that,” said Miss Dean. “So here is another use for water glass, or sodium silicate. It cheapens the soap, so that it can sell for about the same price as the yellow or rosin soap. But there are other reasons for putting it in.
          ”Water glass gets its name because when spread out in a thin sheet it becomes hard like glass. So when it is put into soap it makes the soap very firm, although the soap may have considerable water in it. Feel how hard these cakes of white laundry soap are. A firm soap does not waste away in using as fast as a softer soap.
          ”Sodium silicate helps to soften water and make clothes clean,” went on Miss Dean, “but sometimes too much is put in, and then that soap may not be good for some kinds of clothing. That is because sodium silicate is an alkali, and very much of almost any alkali in soap harms wool and silk, as she shall find out later. So it is best to understand about sodium silicate, in order to choose the right soap for our purpose.”
          ”Can we test for rosin and sodium silicate?” asked Jimmy, looking at his chemical set.
          ”Yes, but not with the chemicals you have. You may learn those tests in high school. Just now you can be quite sure that all yellow laundry soaps in bars contain rosin, and all white laundry soaps of about the same price as yellow contain sodium silicate. Shall we put a list of soaps on the board under each heading?”
          ”Here is a soap lable which says BORAX,” said Grace. “What is borax?”
          ”Borax is a kind of alkali that is found in the soil in California and some of the neighboring states. When much is in the soil it makes the country a desert, because it is alkaline, and plants cannot thrive in it. The story of how it is taken out of the ground and carried to the nearest railroad is quite thrilling. Perhaps you will get an idea of how it used to be done if you look at the label on some packages of borax, like this, for instance. How would you like to be a miner for borax in a place called Death Valley?
          ”Borax helps a little in softening water and washing our clothes,” went on Miss Dean. “Find the bottle of borax among the builders and see that it looks very much like washing soda. It is not so strong an alkali as washing soda, however, and harms wool and silk much less than some alkalis do.”
          ”There is a pretty test for borax which the boys who have their chemical sets here may make. Each of you may take a little of any of these soaps which say they contain borax. Dissolve some of the borax soap in water, add a little hydrochloric acid from the bottle in your chemical set, and warm the mixture. Meanwhile one of the girls may put some spots of tincture of turmeric on this filter paper. Now, boys, place a drop or two of your mixture on these spots of tincture of turmeric, and dry the paper carefully by holding it over the radiator or over this low flame. Watch!”
          ”Why, the tincture of turmeric is turning from yellow to deep pink?” exclaimed several.
          ”That is a test for borax,” said Miss Dean. “If borax had not been in the soap the boys tested, the yellow color of the turmeric would have remained.
          ”At home, however, we do not need this test, because if borax is in a soap, the label is pretty sure to say so. We must get the habit of reading labels.”
          ”Here is a bottle of liquid marked NAPHTHA,” said John. “Is that in soap too?”
          ”Look and see,” said Miss Dean.
          ”Of course it is,” said the girls. “We saw the label NAPHTHA SOAP long ago.”
          ”Smell of the naphtha,” said Miss Dean.
          ”It smells like gasoline,” said the boys, who had been around automobiles enough to know how gasoline smells.
          ”And it is like gasoline,” Miss Dean said. “Is gasoline used for anything except motor engines?”
          ”Of course,” said Robert. “It’s used to take out grease spots. My father says that mother is always using gasoline to clean my clothes.”
          ”Well, then, why would it be put in soap?”
          Everybody saw the reason.
          ”However, we must not depend too much on this naphtha in soap, which is about the same as gasoline. It is ‘volatile,’ just as gasoline is. (Look up ‘volatile’ in the dictionary and see what the first part of the word means.) So if it is volatile, sometimes there may not be much naphtha left in the soap by the time it reaches us, and we shall have to depend upon the soap itself to remove grease.”
          ”Shall we test for naphtha?” asked John.
          ”No,” said Miss Dean. “It would be hard for us to find enough to make a test. Here again we must read our labels, for they will tell us if naphtha has been put in.”
          ”The soaps in these packages look like blue powder,” said Madge, peering into some opened packages.
          ”Shake some out into water,” said Miss Dean.
          ”They make the water blue. Oh, I see some bluing over there among the builders. So that is why these soaps are blue.”
          ”Yes,” said Miss Dean, “although perhaps bluing is not really a builder. It is added to save the trouble of putting in the bluing separately, when washing clothes. Some people like to put it in first, with the soap, but many others think it a better plan to add the bluing to the last clear rinsing water. How many know how bluing is used in your homes?” asked Miss Dean
          ”Mother uses bluing in little balls or cubes,” said several of the girls, “and puts the clothes through the bluing water last of all.”
          ”It is a matter of choice,” said Miss Dean.
          ”Here is a label for soap which says it bleaches,” said Mary. “how does it do that? Bleaching is making things whiter, isn’t it?”
          ”White clothes sometimes get very yellow from wearing,” said Miss Dean, “especially if they are not dried in the sunshine when they are washed. Sunshine whitens or bleaches cotton and linen clothing. These soaps try to do what sunshine does. They usually bleach by containing a substance which gives out oxygen when the soap is used. Oxygen takes out the stains and yellow color in our clothes.”
          ”We wish our clothes bleached, don’t we?” asked Gertrude.
          ”We wish our white clothes to be white, certainly, Gertrude. But we shall have to remember that these soaps may not do for all colored clothes. They may bleach out the color as well as the stains. Another thing to know about bleaching is this: Even sun bleaching will take away a little strength from our cottons and linens, so the constant use of a bleach may mean that our clothing will be weakened by it. If we can hang our clothes in the sunshine after washing them clean, it will not be necessary to bleach them often. When we do wish to bleach, however, or take out some stains, several of these soaps are good to use.”
          ”How can we test for the bleaching substance?” asked Jimmy.
          ”We can let a strong solution of one of these bleaching soaps stand quietly in a glass,” Miss Dean replied, “and if it gives off oxygen, bubbles of oxygen gas will appear all through the solution. Suppose you try that, Jimmy, with this soap.
          ”There is a beautiful test for an oxygen bleach which I can show you, but which you cannot do for yourselves. I will make a solution of this bleaching soap by mixing some of it with water, add a little dilute sulphuric acid, warm the solution, and pour off the clear liquid into another glass. To this glass I am now adding one drop of this yellow liquid - potassium dichromate - and some ether. Now, after shaking, what change do you see?”
          Everybody said “Oh-h-h!”
          The change was a beautiful blue color, like deep sapphire, in the upper part of the liquid. The class was so pleased with the test that they wanted to do it, but Miss Dean explained the dangers in using ether. It was not very pleasant to breathe (and several of the children nodded their heads, because they had had their tonsils taken out), and she had had to be careful to put out the flame before opening the can of ether. The vapor of ether took fire very easily, she explained.
          ”We haven’t talked yet about these soaps marked ‘Makes No Suds’,” said Jimmy.
          ”They are not really soaps, although they are to be used in place of soaps,” said Miss Dean. “These packages which have ‘Makes No Suds’ on their labels are usually powders which contain something quite new in cleansing. It is a substance called trisodium phosphate. Sodium, you know, is another word for soda, just as potassium is for potash. Who can tell me what the ‘tri’ means in front of sodium? What does it mean in tricycle?”
          Nobody spoke for a moment, so Miss Dean said:
          ”Three. ‘Tricycle’ means ‘three wheels,’ just as ‘bicycle’ means ‘two wheels’.”
          ”All right, this substance called trisodium phosphate has three parts, or, as the chemist would say, three unit weights, of sodium in it. Find the bottle containing trisodium phosphate among the builders. It makes a fine water softener, better even than washing soda.
          ”Put some of the powder in the water and shake it. Does it make suds?”
          ”No, Miss Dean.”
          ”We learned, you remember, that when soap is making suds it is doing the work of cleansing,” said Miss Dean. “Trisodium phosphate is quite a strong alkali, so how may it cleanse, even though it does not make suds?”
          ”In the way that the alkali in soap does, I suppose,” said John.
          ”Yes,” said Miss Dean, “and we may find that these powders are too strong with alkali to be used for all purposes.”
          ”What are they good for?” asked Grace.
          ”Can you think of any use for a cleanser where suds would be a nuisance?” asked Miss Dean. “Suds is apt to leave streaks unless it is carefully rinsed off.”
          ”Washing windows?” asked thoughtful Mary.
          ”Exactly,” said Miss Dean, “and bottles, like milk bottles, and glassware in general. And we must not forget its good work in softening hard water, so that soap can be used without waste.”
          ”How shall we know which packages contain trisodium phosphate?” asked Jane.
          ”By the label, which usually says ‘Makes No Suds,’ and by shaking a little of the cleanser in water to find out. Sometimes a little soap is put in these cleansers, but not often.”
          ”And here is a chemical test which you who have the sets may try,” went on Miss Dean. “Make a water solution with some of the powder, add a few drops of nitric acid, and warm the mixture. Be careful not to let the nitric acid touch your fingers or clothes, for it will burn. Now pour off the clear part, and add a few drops of it to this liquid with a big name - ammonium molybdate. Warm your test tube in this cup of hot water and watch for a change.”
          The change came in a moment. Clear yellow crystals began to form until the liquid was full of them. The boys decided that they would get some ammonium molybdate for their chemical sets and be ready to test for trisodium phosphate at home.
          And then Miss Dean said:
          ”Now that we have finished testing for builders, and have put our soaps into lists, let us make two big lists of all our soaps, one list for those which are strong soaps, and one for those which are milder. What did we decide that those words meant, when we were talking about how soap cleanses?”
          ”Strong soaps have much alkali and mild soaps do not,” said Robert.
          ”All right,” said Miss Dean. “Here is a rough way to compare soaps as to whether they are strong or mild. Please put your soaps again in the little saucers, as you did before. Now take this bottle of phenolphthalein, and put a few drops right on the dry soap. Phenolphthalein turns pink if it touches alkali, so you can see whether alkali is present or not. You may also compare the soaps as to the amount of alkali present. Those having much alkali will turn very pink, those having a little will turn less pink, and some very mild soaps will not turn pink at all. This test, however, does not tell us the kind of alkali present; whether it is caustic soda, or washing soda, or some other kind. Now, begin, and watch.”
          ”This one is a deep pink,” said John.
          ”And this is still pinker, almost red,” said Grace.
          ”These soaps don’t show any pink at all, or only a tiny bit,” said Jane.
          So they went on through all the soaps, and when they finished there were about fifteen saucers showing different shades of pink.
          ”Let us show a deep pink in the ‘strong’ list, and those which show only a trace of pink, or none at all, in the ‘mild’ list. These lists will help you a great deal in learning how to choose soaps for different purposes. We will leave them on the board until all have had time to copy them.”
          ”But we haven’t finished talking about kinds of soaps, have we?” asked George, anxiously.
          ”Haven’t we?” asked Miss Dean, smiling.
          ”No, indeed,” said George. “Don’t you remember I wanted to know why some soaps float?”
          ”That is so,” said Miss Dean, “and the answer is very simple. Floating soaps have enough air beaten into them while they are cooling to make them lighter than water.”
          ”Is that all?” said George. “Well they’re good soaps for the bathtub. A fellow doesn’t have to fish all around the bottom of the tub when the soap slips out of his hands.”
          ”And he doesn’t skid, as he might on a cake of soap when it does go to the bottom,” said John.
          When the class began to copy their list from the board, they found they had soaps containing: