Q.ers." The recipe called for 2 tablespoons of ammonium carbonate per 5 cups of sifted flour. I purchased some ammonium carbonate from the pharmacy. The package read: "Warning! Harmful if swallowed. Wash thoroughly after handling."

Is this a poison? Did people die from ammonium carbonate poisoning after eating crackers? Since I have already purchased the product, I plan to use it if it is safe.

A. Ammonium carbonate is an alkaline salt. When dissolved in water, it produces ammonia gas (the smell of liquid ammonia), which dissolves in the water to form a strong base, ammonium hydroxide. In concentrated form, strong bases cause severe damage to delicate tissues such as the lining of your nose and mouth. Hence, ammonium carbonate is harmful if swallowed.

Every substance is toxic in some amount and in some way. Ammonium carbonate belongs to a category of substances that are safe when handled properly, dangerous if abused. Vinegar is equally noxious if handled carelessly. So is baking soda. These are tissue irritants, not substances that block transmission of nerve impulses, build up in your liver or cause cancer.

Ammonium carbonate is still used by the cookie industry in place of baking powder. It releases gas explosively, causing a very rapid rise before a dough or batter sets. It's smelly, however, due to the release of ammonia in the air. Ammonia doesn't remain in the product due to its extreme volatility at such high temperatures.

There is really no point in keeping ammonium carbonate at home. Baking powder is easier to use and has a longer shelf life. Ammonium carbonate, on the other hand, loses much of its gasifying power as it sits on a warm kitchen shelf.

I have been making french bread according to Julia Child's recipe for several years now, but using the food processor for mixing. In the past, I had good luck. Now I am using the new, faster yeast, and the loaves are emerging from the oven pale and heavily shredded. Why?

Yeast produces enzymes called proteases that split the gluten formed during mixing into smaller and smaller pieces. Initially, gluten is a cohesive network that gives dough its elasticity and extensibility. If the network is seriously damaged before baking, however, the bread acquires a pitted surface that may even look shredded if it can't hold its crust together while rising. In addition, the interior of the bread turns crumbly and dry.

The paleness comes about when the yeast cells use up all available sugars in the dough. They then begin consuming maltose, which they leave until last as they find it difficult to absorb and digest. Once the yeast cells start to use maltose, however, the bread loses its browning ability.

You can do one of four things to prevent these problems. One, you might shorten the bread dough's rising times considerably. Two, you might use ice water in the dough to slow the yeast's metabolic rate and proof the dough in a cool spot. Three, you might add more sugar to the dough; there's a risk to that, however, as the yeast cells would still produce proteases and degrade the gluten. And four, you might switch back to the old yeast.

I don't really like using the fast yeast in breads. It produces a fine texture approaching that of supermarket sandwich breads. It does a good job in danish and croissant doughs, however.