What's with the information I found on an Orville Redenbacher's popcorn box? Why do they give the calories and other nutrition information for both unpopped and popped? Why are there more calories in unpopped popcorn than popped? There's also more fat, sodium and fiber in unpopped. My husband believes some government regulation requires this. Can you explain?

First of all, your husband is correct, in that the Food and Drug Administration requires the labeling of products as the consumer receives them, not after the consumer has cooked or popped them.

The box I have in front of me (and Orville has almost a dozen kinds on the shelf, all with different nutrition numbers) says that 35 grams of unpopped kernels make about four cups popped. But the number of cups of popped corn I am able to get from 35 grams of kernels will depend on the power of my microwave oven. A lower-powered oven will turn out fewer cups of popped corn because it leaves behind more "old maids." So the "4 cups of popped per 35 gram serving" can be only a rough guide.

If the numbers of calories and grams of fat turn out to be higher in the unpopped product than in the popped corn (as they also did in my case), it's not because of any loss of nutrients during the popping process. It's simply due to the approximate nature of the "4 cups" figure.

Then why do they even bother to give the amounts of nutrients in the popped corn? According to a sweet, recorded voice on Mr. Redenbacher's customer service line, they are listed only for the consumers' convenience, so that we can measure the number of cups of popped corn we consume and multiply it by the number of calories and grams of fat per cup.

Yeah, sure. Don't we all do that?

I recently bought Post Alpha-Bits for my 6-year-old daughter, thinking that it was a healthy cereal. I was therefore surprised to see that one of its ingredients is propylene glycol, a petrochemical that my dictionary tells me is used in antifreeze and brake fluids. What's it doing in Post Alpha-Bits?

You might be tempted to think that with winter coming on, it's a good idea to fortify your daughter with antifreeze. But that's not the way chemicals work. Just because a chemical is used in an unsavory industrial application doesn't make it inedible. For example, the salt on your table can be used to supply chlorine for the manufacture of insecticides.

Propylene glycol and ethylene glycol are both syrupy liquids derived from glycerin. They are used in antifreeze because they mix well with water and reduce its freezing temperature to well below 32 degrees without themselves freezing.

But there is a vital difference between these two chemicals: Ethylene glycol is poisonous, while propylene glycol is a food additive "generally regarded as safe" by the FDA. Propylene glycol is added to foods and cosmetics as a humectant -- it retains moisture. You can find it in such foods as shredded coconut, beverages, baked goods, toppings, icings and cereals. The nonprofit Environmental Working Group has a database (www.ewg.org/reports/skindeep/chemhealtheffect.php?chem_id=4162) of almost 2,000 cosmetic products containing propylene glycol.

In the radiators of our cars, however, propylene glycol has largely been replaced by the poisonous ethylene glycol, usually dyed a fluorescent green so mechanics can detect leaks with ultraviolet light. It has a sweet taste and is particularly lethal to cats, rabbits and dogs.

But remember: That's the evil ethylene, not the helpful propylene.

I recently purchased some crackers and noticed that reduced iron was one of the ingredients. What is reduced iron? Does it have to do with the ferric/ferrous oxidation states? What does it contribute to the crackers?

The iron is in the flour from which the crackers are made. You'll see "reduced iron" among the ingredients of many wheat, corn and other grain products, often in breads, pastas and breakfast cereals. It's part of the vitamin and mineral enrichment of refined flour.

As you obviously know, iron can exist in three so-called oxidation states: ferric iron, ferrous iron and elemental or metallic iron. Iron ores are found mostly in the ferric form. At the refinery, they are "reduced" (in chemical lingo) to the metallic form. Iron metal is therefore sometimes called reduced iron.

Foods may also be fortified with iron in its ferric or ferrous forms, most often as ferrous sulfate. All three forms are absorbed by the body, but the ferrous form is more readily metabolized.

While prowling the cereal aisle of my supermarket, I noted that Post Raisin Bran, Kellogg's Special K, Keebler Club Crackers and Nabisco Saltine Crackers, among many other products, are made from reduced iron-enriched flour. Wonder Bread, however, is enriched with ferrous sulfate.

So are you eating actual pieces of iron metal in your reduced iron-enriched crackers and cereals? Believe it or not, you are. But the metal is in the form of a very fine powder, consisting of particles less than 45 microns, or 0.0018 of an inch, across. When you eat these tiny particles of iron, they simply dissolve in the hydrochloric acid in your stomach and are transformed into the ferric or ferrous state anyway before being absorbed.

And there's no need to stay away from magnets.

LABELINGO: Perspicacious reader Ellen Kominers Bethesda saw the following sign in the Rockville Pike Giant supermarket: "Notice to our Customers: Milk Prices Have Increased Due to Increased Cost of Ingredients."

Have those darn cows raised their prices again?

Robert L. Wolke (www.robertwolke.com) is professor emeritus of chemistry at the University of Pittsburgh. His latest book is "What Einstein Told His Cook 2, the Sequel: Further Adventures in Kitchen Science" (W.W. Norton, 2005). He can be reached at wolke@pitt.edu.