How does the meaning of pure substance different for a common man than to a chemist? Explain.

A pure element or compound contains only one substance, with no other substances mixed in it.

For a common man, pure substance means that it is not adulterated. For example, for a common man, pure milk means the liquid material that is given by cow or buffallo and it is not mixed with water or other materials to thicken it. But for a chemist, any milk is not a pure substance. Milk is a mixture of water, fats and proteins. These materials are different in milk obtained from different sources. Similarly pure fruit juice for a common man means is that it is not mixed with fruit juice of other fruits or water or salt. But for a chemist any fruit juice is a mixture of water and several other substances. For a common man pure gold means gold of a given composition. But a chemist knows that no ornaments can be made from pure gold. All ornaments of gold contain gold and copper.