Many substances on earth fit neatly into categories of solid, liquid, or gas. But many of the foods and condiments we eat don't fit well. They belong to a group of materials called colloids. These generally contain two different materials which co-exist without complete mixing. Often one exists as particles, fibers, or films surrounded by the second. The first is separated or dispersed into portions not directly attached to each other. The other portion is continuously connected. We apply different names depending on the physical states of the dispersed and continuous phases.
These typically are all opaque to light, appearing cloudy because the dispersed phases are large enough to scatter light rays. Two samples of gases will completely mix forming a gaseous solution so that a colloid composed of two gas phases is impossible. The same is true of liquids which are soluble in each other. But liquids which have low solubilities such as polar and non-polar liquids (such as water and oil), which would ordinarily separate with one floating atop the other can form a colloid (an emulsion) if a soapy substance called an emulsifier is used. These emulsifiers are typically molecules with a polar end attached onto an otherwise longer non-polar molecule.
One might first think it would be impossible to have two continuous phases. Indeed that would be true in a two-dimensional world. A gel gets past this by weaving relatively continuous fibers amongst a continuous liquid.
One common kind of gel is composed of protein fibers derived from connective tissue surrounded by a water solution with coloring, flavoring and sugar. One commercial brand is Jello. The gel is produced by dissolving the protein in boiling water. As the mixture is allowed to cool the fibers entrap the liquid is a structure that increasingly becomes rigid. This can be used to investigate the colloid called gel. These gels have a wide variety of uses. For example disposable diapers have a small amount of powder which is capable of capturing a large amount of urine in the form of a gel.
The Joy of Cooking describes making of a perfect mayonnaise as the Sunday job for Papa in France. It was first called Mahonnaise after a French victory over the British at Port Mahon on the Island of Minorca. It has been made by hand for over 300 years. The combination of oil and water (lemon juice or vinegar), held together by egg yoke as its emulsifier, needs to be refrigerated to deter deadly and hard to detect bacteria growth. Caution: if you wish to consume the mayonnaise, clean all equipment and utensils and maintain cleanliness to assure the food remains uncontaminated.
oil mark.If oil is the continuous phase it will soak through the paper leaving a darker transparent patch. If water is the continuous phase there will be no effect on the back side of the paper.
Communicating technical information such as observations and findings is a skill used by scientists but useful for most others. If you need course credit, use your observations in your journal to construct a formal report.