The Principles of Exchangeable Value of Commodities

Money has become in all civilized nations the universal instrument of commerce. What are the rules which men naturally observe in exchanging them either for money or for one another? These rules determine what may be called the relative or exchangeable value of goods. Nothing is more useful than water but it will purchase scarce anything. A diamond on the contrary has scarce any value in use but a very great quantity of other goods may frequently be had in exchange for it. And lastly, what are the different circumstances which sometimes raise some or all of these different parts of price above and sometimes sink them below their natural or ordinary rate?