Liquid crystals are examples of anisotropic liquids. Solvents can be gases, liquids or solids. Dielectric materials can be solids, liquids, or gases. Pure sulfur mustards are colorless, viscous liquids at room temperature. Solids, liquids, and gases have stress fields. It may occur due to release of radioactive gases, liquids or particles. Refractive index is used to measure solids, liquids, and gases. This occurs naturally in liquids and solids. Breakdown mechanisms differ in solids, liquids, and gasses. Heaters exist for various types of fuel, including solid fuels, liquids, and gases. A reaction between two gases or two miscible liquids is homogeneous. The effect of pressure and temperature on the densities of liquids and solids is small. It is used to separate fine substances from liquids or air. Working in a clean area free of flammable liquids, materials and gases is very important. Convection is usually the dominant form of heat transfer in liquids and gases.