Soap is one of the earliest inventions ( اولین اختراعات ) of humans. It was first made almost 5000 years ago. Soap is a type of salt! But please don't put it in your food. 
Soap is made from mixing an acid with a base.
acid: Acids are things that can give hydrogen to something else. Mixed with water, they are things that taste sour ( ترش ). Lemon juice, orange juice, tomato juice, and black coffee are examples of acids.
hydrogen: Hydrogen is simplest ( ساده ترین ) member of the chemical family. It is the lightest ( سبک ترین ) of all the elements ( عنصر ) on earth. Hydrogen is a gas ( گاز ) that has no color, no taste, and no odor ( بو ).
base: a base is something that can accept ( پذیرفتن ) hydrogen from an acid.
How is soap made?
For many years soap was made from mixing ashes ( خاکستر ), animal fat ( چربی حیوانی ), and water. This made a very strong salty mixture ( مخلوط نمکی ). It was ready when it would melt ( ذوب شدن ) a chicken feather! The ash was mixed with fat and boiled ( جوشیدن ) over an outdoor fire for many hours until a soft soap was formed.
It was difficult to control the quality of soap making it from ashes. So today, soap is usually made from mixing oil (beef fat, coconut oil or olive oil) with lye. Lye is made from salt. When you add lye to the oils, together with water and heat, it turns into soap.
How does soap work?
Soap cleans by dissolving grease ( چربی ذوب ). Soap molecules* ( مولکول ها ) have one end that bonds ( پیوستن ) with water. The other end bonds with grease. The soap molecules that bond with grease dissolve ( ذوب شدن ) the grease and break it up ( شکستن ) into smaller parts. When your hands are soapy, the molecules lift ( بلند کردن ) the dirt and oil away from your skin. Then water can wash it away.
• atom: the basic unit or building block ( بلوک ساختمانی ) of all material (مواد) things. • molecule: one or more atoms that hold together and have the same qualities ( کیفیت ها ). A molecule is the smallest unit ( واحد ) that can have a chemical ( شیمیایی ) reaction ( عکس العمل ).
