Good info. Remember that the invention of refrigerated rail cars primary impact was on the ability to ship meat to urban centers so that you didn't have to bring the entire cow or hog into town. Industrial Technology contributed more to transportation, preservation and "purification" of foods than anything else. From what Wikipedia says, baking soda as we know it was invented in the 1790's in France, but the first factory that made it commercially wasn't opened until 1846 in New York. With that said, apparently the Egyptians were using some naturally occurring analogue many moons ago, so who knows? Suffice to say that there have been substances around for millenia that do the same basic things that our modern kitchen products do, albeit not as efficiently. The question, as in all of these discussions, is not what could have been used, but one of general availability at the time and in the place that we are talking about. Some of the stuff we now use at home, like "store bought" yeast, might have been available in bulk form only to commercial bakers in the early 1800's. With that said, I haven't seen a "modern" biscuit or cornbread recipe that calls for dry active yeast that I can remember. The all use some combination of baking powder and baking soda.