Other and minor decompositions likewise occur, such as the partial conversion of the starch into dextrine, the sugar into lactic acid, and the alcohol into acetic acid, but the most essential change is the production of alcohol and carbonic acid. The alcohol formed is mainly volatilised, although an average proportion of 0·3 per cent. of this compound has been found in samples of fresh bread. The escape of the carbonic acid is retarded by the gluten, and to its expansion is due the porous or spongy appearance of well-made bread. Of late years, artificial substitutes for the fermentation process in the production of porous bread have been extensively employed. By the use of these agents, the liberation of carbonic acid in the dough is accomplished and a slight gain of weight is effected, as none of the original ingredients of the flour are lost by fermentation. “Aërated bread” is made by kneading the flour under pressure with water highly charged with carbonic acid gas, which, upon the removal of the pressure, expands, and gives porosity to the bread. The use of “baking powders” effects the same result in a more convenient manner, and is largely practised in families. These compounds generally consist of sodium bicarbonate (sometimes partially replaced by the corresponding ammonia salt), and tartaric acid, or potassium bitartrate, together with rice or other flour. A more commendable preparation is a mixture of sodium bicarbonate with potassium or calcium acid phosphates, the use of which is claimed to restore to the bread the phosphates lost by the removal of the bran from the flour. Baking powders are often mixed in the dry state with flour, and the produce, which is known under the name of “self-raising flour,” only requires to be kneaded with water and baked to form porous bread. However great the convenience attending the use of these compounds, they are often open to the objection that their decomposition gives rise to the formation of aperient salts, _e.g._ sodium tartrate, and that they are very frequently contaminated with alum.