Pompoms of soap

1998/01/01 Bandres Unanue, Luis Iturria: Elhuyar aldizkaria

• Fisika

The truth is that in our usual conversation these punpuiles do not have very good fame and we use them to make some comparisons. But in the field of physics it is very different. “Make a tip of soap and look,” wrote the prestigious physicist Kelvin. Although you spend all your life researching, you will always draw new knowledge from physics.”

The admirable polychrome layers that appear in these thin layers of soap allow the physical to measure the wavelengths of the luminous waves. On the other hand, the investigation of the tension of these layers, the law of forces that appear between the fractions, allows us to understand, that is, the forces of cohesion. Without cohesion the world would be just a lot of powders.

Ch. Boyce is an English physicist who offers a long series of experiments with pointers in his book entitled “soaps”. We only bring one or the other, but whoever has special interest in this topic knows where to go.

To make our tips we will use traditional kitchen soap, since the bathroom does not serve for it. If possible, soaps of olive oil or empty almonds are recommended, for being the most suitable for this purpose.

For dissolution to occur, we will melt a piece of soap in clean, cold water until you get a fairly compact liquid. The ideal is to use rain water or clean snow water, otherwise we will take boiling and cooled water. To achieve a longer duration of the spikes, Plateau indicates that a third of its glycerin volume must be added to the dissolution. The foams and punpuiles that are formed will be removed with an arbor. Once this is done, we introduce to the dissolution the end of a clay tube. With a straw of about ten centimeters, good results are also obtained, but for this you have to cut the lower end on cross.

For the realization of the tips, follow the following steps: put the end of the tube into dissolution and keep it vertically until a liquid membrane appears at its end; then we will blow. In doing so, the punpuil is filled with the hot air coming out of our lungs, which makes the punpuil full rise quickly.

If the first punpuil obtained has a diameter of approximately ten centimeters, the soap mixture made is good; otherwise, we should put more soap until we have the punpuil of that diameter. But this is not enough. After making the punpuil we dip a finger with a mixture of soap and try to put it in the punpuil; if the punpuil bothers us we could start with the experiments, if it is washed, we have to put a little more soap.

The experiments should be carried out with calm and much attention and in a very clear room, since otherwise the spikes will not show us their beautiful polychrome reflections.

A flower inside a soap pump

Pour soapy water into a plate up to a layer of two or three millimeters. In the center of the plate we will place a florite or something else and cover it with an onyl of glass. Then, and as we blow through the canutillo of the onila, we will raise the basket little by little, as seen in the image. Punpuil soap is being made and when this is quite large we will leave it free. The florite, or other small piece, will be surrounded by a transparent semisphere in which all the colors of the rainbow will be reflected.

Instead of putting the flower you can put a statuette and on itself you can put a small punpuil as a crown. To do this, you have to place a drop of soap water on the head of the statuette and then, after making a big punpuil, pass it with a little bit and blow inside the small punpuil.

Punpuiles inside another punpuil

As we have said with the onila used previously, a large punpuil is manufactured. Then, take a straw and once wet one end in soap water, we carefully cross the layer of the big punpuil until reaching the center. Then, blowing, we make the second punpuil and gradually remove the straw to the outside. If you want, within the second punpuil you can do another in the same way, etc.

The punpuil soap layer is all the time in tension and presses on the air inside.

If we approach the canutillo of the onila to the flame of a candle we will see that the strength of these membranes is not so small: the flame deviates clearly.

One of the worst ideas about the pointers is the duration. Most consider that they last very little, but if used with care they can last several years. The English physicist Dewar, famous for his work on liquefaction of air, stored soap pompoms in special bottles and the American Lawrence managed to keep them in a special container for several years.

To finish with this portillo, we will take care of the layer of punpuiles. These are the finest things that can be seen at first glance. In most cases, the thickness of the objects used for the comparison of fineness is much greater than that of the layer of spikes: we often say that one thing is “as thin as a hair”, but the thickness of the layer of punpuil is five thousand times smaller than that of a hair. This means that, while a human hair increased two hundred times a centimeter thick, doing the same with the chisel layer, it would still be almost invisible. To see the section of the layer as a fine line we should multiply it by two hundred times, that is, fifty thousand times, and then the hair would have a thickness of two meters.