Eddie Choate, age 8, of Indianapolis, Ind., for his question:

What is 18 carat gold?

The carat is a weight used to measure gem stones. It is equal to 200 miligrams and a diamond of one carat is quite a valuable piece of property. This gem‑weight carat, however, has nothing to do with the 18 carat quality of gold. The word carat used in this sense means one‑24th part.

Gold is a soft metal and, for durability, is alloyed with other metals, usually silver. Pure gold is 24 carat, or all 24 parts gold. In a piece of more durable 18 carat gold the alloy contains 18 parts of gold to six parts of silver or other alloy. More gold and less silver makes a more valuable alloy, but it may not wear as well. The most valuable alloy,but not necessarily the most durable, is 22 carat gold.