The Conservation of Matter
The conservation of matter is demonstrated by the reaction of "red" with "white" to form the product "blue." The mass of the matter at the end of the reaction is the same as that of the starting materials used for the reaction.
You must be a bit careful with this kind of reasoning, however, because reactants are frequently not completely used up. For example, consider the reaction of iron with oxygen to form ferric oxide (Fe2O3, rust). If a 5.6 gram piece of iron is immersed in 10.0 g of oxygen and the iron is completely converted to rust, it might seem that the amount of rust should be 5.6 + 10.0 = 15.6 g. In fact, only 8.0 g of rust will be formed and 7.6 of oxygen will also be present.
Deflection Of Electrons In The Cathode Ray Tube By An Electric Field
A hollow glass tube is fitted with two metal plates and most of the air is removed from the tube. When the metal plates are connected to a source of high voltage, electrons are emitted from the negatively charged plate, the cathode, and travel to the positively charged plate, the anode. Some of the electrons travel through holes in the anode and strike the glass causing it to glow. When the cathode ray tube is surrounded with oppositely-charged plates, the electrons are attracted to the positively charged plate and strike the glass on that side of the tube.
This animation is designed to illustrate one of the most important principles in chemistry. Two charged particles that have the same charge repel each other, while particles with opposite charges attract each other. In other words, if two particles both are deficient in electron density and therefore are positively charged, they will repel one another. If one is deficient in electron density, while the other has an excess of electrons, the particles will attract one another.