In all these preparations of yeast and dough, it should ever be recollected that “the process of fermentation cannot go on when the temperature is below 30° F., that it proceeds quite slowly at 50°, moderately at 60°, rapidly at 70°, and very rapidly at 80°.” If, therefore, it is desired to have the yeast or dough stand several hours before it is used or baked, it should be kept at a temperature of about 50°. But in the ordinary way of making bread, a temperature varying from 60° to 70°, or about summer heat, is perhaps as near right as it can well be made. Prof. Thomson gives the following directions for making yeast in large quantities:—“Add ten pounds of flour to two gallons of boiling water;—stir it well into a paste, let this mixture stand for seven hours, and then add about a quart of good yeast. In about six or eight hours, this mixture, if kept in a warm place, will have fermented and produced as much yeast as will make 120 quartern loaves” (of 4 lbs. each.) A much smaller quantity can be made by observing due proportions of the ingredients. To raise bread in a very short time without yeast, Prof. Thomson gives the following recipe: “Dissolve in water 2 ounces, 5 drams and 45 grains of common crystallized carbonate of soda, and mix the solution well with your dough, and then add 7 ounces, 2 drams and 22 grains of muriatic acid of the specific gravity of 1,121, and knead it as rapidly as possible with your dough;—it will rise immediately—fully as much, if not more than dough mixed with yeast—and when baked, will be a very light and excellent bread.” Smaller quantities would be required for small batches of bread. A tea-spoonful or more (according to the quantity of dough or batter) of super-carbonate of soda dissolved in water, and flour stirred in till it becomes a batter, and then an equal quantity of tartaric acid dissolved and stirred in thoroughly, will in a few minutes make very light batter for griddle or pancakes; or if it be mixed into a thick dough, it will make light bread. Good lively yeast, however, makes better bread than these alkalies and acids: howbeit these are very convenient in emergencies, when bread or cakes must be prepared in a very short time; or when the yeast has proved inefficient. We see then that wheat meal consists of certain proportions of starch, gluten, sugar, bran, &c.; and that in making loaf bread, we add yeast or leaven, in order to produce that kind of fermentation peculiar to saccharine matter or sugar, which is called vinous, and by which the gas or air is formed that raises the dough. But the sugar is an incorporate part of every particle of the meal, and is therefore equally diffused throughout the whole mass; and hence if we would make the very best loaf bread, the fermentive principle or yeast must also be equally diffused throughout the whole mass, so that a suitable portion of yeast will be brought to act at the same time on every particle of saccharine matter in the mass.