The decomposition of phosphoric acid, although there is no detailed chemical understanding in ancient times, can be inferred according to common sense and some old knowledge.

Phosphoric acid is easily divided when heated. When it decomposes, a variety of products may be produced. Under specific conditions, phosphoric acid can be decomposed to produce phosphine and phosphoric acid, etc. During this change, the molecular structure is broken and new things are formed.

Looking at various physical properties, phosphoric acid has a specific chemical activity. Under the action of heat, it is chemically bonded and cracked. Or due to the energy of heat, the atoms in the molecule are rearranged to form a new material form.

When decomposing, there may be a change in color, or there may be a gas escape. This is a characterization of its decomposition process. Although the ancients did not remember it in precise chemical language, they could feel the difference in its changes by the way they viewed things at that time.

In short, the decomposition of phosphoric acid is a chemical change, which is caused by its nature and external conditions. Although there is no detailed history, it can be rationalized.