Tony Logsdon, age 13, of Madison, Indiana, for his question:

 Is it true that magnesium is present in sea water?

Magnesium is a silvery metallic element, lightweight and very strong. It has countless uses in our modern, metal minded world and our best sources of magnesium are the invisibly small particles of the metal dissolved in the world's oceans. Sea water, of course, contains an immense amount of assorted chemicals. Their average proportions have been estimated in a cubic mile sample of sea water. The amount of magnesium in this standard sample is estimated to be about six million, one hundred and twenty five thousand tons. Yes, tons. America uses about 75,000 tons of magnesium a year and most of it is extracted from sea water by an ingenious chemical process.

This question gives Andy a chance to correct an error. Some weeks ago he reported the amount of gold estimated to be in a cubic mile sample of average sea water. The actual figure is 38 pounds of gold per cubic mile. But somehow the pounds were re¬ported as tons. So correct your notes and try not to feel miffed to learn that the amount of gold in the sea is 2,000 times less than Andy said it was. After all, for a few weeks, the error did allow us to enjoy a most lavish vision of treasure trove.