Each has its appropriate office to fulfil during the process of incubation or hatching; and one acts in the mysterious process as important a part as the other. If we remove this glairy fluid from the shell and place it in a glass, and plunge into it a strip of reddened litmus paper, a blue tinge is immediately produced, which indicates the presence of an alkali. The alkali is soda in a free condition, and its presence is of the highest consequence, for without it the liquid would be _insoluble_. A portion of the white of an egg, when diluted with water, and a few drops of vinegar or acetic acid added to it, undergoes a rapid change. The liquid becomes cloudy and flocculent, and small bits of shreddy matter fall to the bottom of the vessel. This is pure albumen, made so by removing the soda held in combination by the use of the acid. A pinch of soda added to the solid precipitate redissolves it, and it is again liquid. There is another way by which the albumen is rendered solid: and that is by the application of heat. Eggs placed in boiling hot water pass from the soluble to the insoluble state quite rapidly, or, in other words, the albumen both of the white and yolk becomes "coagulated." No contrast can be greater than that between a boiled and unboiled egg. Not only is it changed physically, but there is a change in chemical properties, and yet no chemist can tell in what the change consists. It is true, the water extracts a little alkali, and a trace of sulphide of sodium; but the abstraction of these bodies is hardly sufficient to account for the change in question. The hardening of the albumen of egg by heat constitutes the cooking process, and this deserves a moment's consideration.