We will suppose that after the strenuous course of cooking, washing, and cleaning outlined for the morning, that the housekeeper still has strength to make soda biscuits for tea, and we will study the chemical action involved.

One of the first chemical methods of securing carbon dioxide to use in making bread rise, was by putting hydrochloric acid and cooking soda together in a dough which might be put into the oven before the gas escaped from it.

Cooking soda is a salt called bi-carbonate of sodium. It differs from the ordinary mono-carbonate of soda (washing soda) in yielding twice as much carbon dioxide in proportion to the sodium part of the compound. The saleratus of our grandmother's time was bi-carbonate of potash, made from wood ashes. The name is still used, but at all stores, cooking soda would be delivered invariably if saleratus were asked for. The true saleratus costs ten times as much as the soda and is no more effective. The carbonic acid is easily set free by chemical compounds of an acid nature, and new chemical compounds result.

Cooking Soda

Experiment. Put a little cooking soda into any acid - lemon juice, vinegar, almost any fruit juice - and the carbon dioxide will be seen to escape in tiny bubbles. Part of the acid unites with part of the soda, forming a new salt, and the acid taste will be much reduced or lost.

Part of the carbon dioxide in sodium bi-carbonate is driven off by simply heating, leaving ordinary sodium mono-carbonate, washing soda. In using this process, cooking soda is mixed with the flour. The high temperature of the oven drives off carbon dioxide, and the bread puffs up. It is light, but yellow in color. The sodium carbonate remains in the bread and its alkaline nature serves to neutralize the acid fluids of the stomach (gastric juice) so that digestion of the bread may be retarded. The sodium carbonate also acts in some way upon the gluten producing an unpleasant odor.

Among the first methods proposed was one undoubtedly the best theoretically, but very difficult to put in practice. This depended upon the liberation of carbon dioxide from bi-carbonate of sodium by means of muriatic acid - the method already described. The liberation of gas is instantaneous on the contact of the acid with the "soda" and even a skilled hand can-not mix the bread and place it in the oven without the loss of much of the gas. Tartaric acid, the acid phosphates, sour milk (lactic acid), vinegar (acetic acid).

Heating

Cooking

Soda

Early Experiments alum, all of which have been used, are open to the same objection.

Cream of tartar is the only acid substance commonly used which does not liberate the gas by simple contact in cold solution. It unites with "soda" only when heated, because it is so slightly soluble in cold water.

Experiment. To illustrate this stir a little soda and "cream of tartar" into some cold water in a cup. In another cup mix the same amounts of each in warm water. Note the difference in the action produced.

To obtain an even distribution of the gas by thorough mixing, cream of tartar would seem to be the best medium by which to add the acid, but because there are other products which remain behind in the bread in using all the so-called baking powders, the healthful-ness of these residues must be considered.

Common salt is the safest residue and perhaps that from acid phosphate is next in order.

The tartrate, lactate, and acetate of sodium are not known to be especially hurtful. As the important constituent of Seidlitz powders is Rochelle salt, the same compound as that resulting from the use of cream of tartar and "soda," it is not likely to be very harmful, even in the case of the habitual "soda biscuit" eater, because of the small quantities taken.

The various products formed by the chemical decomposition of the alum and "soda" are possibly the most injurious, as these are sulphates, and are thought to be the least readily absorbed salts. The sale of "alum" baking powder is increasing, as it is cheaper. Taking into consideration then the advantage given by the insolubility of cream of tartar in cold water, and the comparatively little danger from its derivative - Rochelle salt - it would seem to be, on the whole, the best substance to add to the soda in order to liberate the gas, but the proportions should be chemically exact, since too much alkali would hinder the process of digestion. Hence baking powders prepared by weight and carefully mixed, are a great improvement over cream of tartar and "soda" measured separately. As commonly used, the proportion of soda should be a little less than half.