688 THE POPULAR SCIENCE MONTHLY. 



The starch of every plant differs from its neighbors both in size 

 and shape, and this has a considerable influence on the character of 

 the vegetable organ in which it is stored up ; the hardness of rice, for 

 instance, being due to the fact that rice-granules are extremely minute, 

 with angular corners which fit closely and firmly together ; whereas 

 potato-starch is large and round, with considerable interspaces filled 

 with water, and so forms a comparatively soft mass. But, notwith- 

 standing their outward points of difference, in chemical composition 

 the starches are all identical, consisting of carbon, hydrogen, and 

 oxygen exactly the same materials as sugar is composed of, and bet- 

 ter known as the component elements of coal and water. Leaving the 

 many varieties of starch in the mean while, let us consider one species, 

 namely, that of wheat, because it is the most important in this country, 

 forming the basis of our daily bread. 



An ordinary grain of wheat, if sliced through the middle and ex- 

 amined as to its structure, will be found to consist of several layers, 

 the outer a hard coating, which contains mineral salts, lime, sand, etc. 

 Beneath this is a zone of matter very rich in gluten, the flesh-forming 

 constituent of the wheat ; while the central portion of the grain is 

 occupied by a white, powdery mass, which is nearly pure starch. In 

 manufacturing flour, the two outer layers, which together form the 

 bran, are usually removed, leaving the white starchy flour of the cen- 

 tral portion. 



Let us now briefly consider the chief points in the chemistry of 

 bread-making. If flour be worked up with water, it forms a sodden, 

 insipid, indigestible mass ; but, if heated to the temperature of boiling 

 water, the starch-granules burst ; and it is thereby rendered a little 

 more digestible, although still forming a close, stiff, and not very pal- 

 atable cake. Such is the character of unleavened bread, and of sea- 

 biscuits, a slightly different form of the same thing. To be fit for 

 digestion, starch must be dissolved or softened by boiling or baking ; 

 hence the reason why raw nuts are so indigestible as compared with 

 the favorite roasted chestnuts ; and hence one reason for cooking food, 

 which mankind has been taught by experience, ages before chemistry 

 could give a scientific explanation of the reason why. Cooking is, in 

 fact, a partial digestion ; and the same is the case with baking, both 

 being preliminary aids to the changes which take place in the mouth 

 and stomach before the food is in a fit state for the preparation of the 

 blood. Accordingly, we bake our bread ; and we bake it in the way 

 we do because a soft, spongy loaf is more readily moistened and acted 

 on by the saliva and the juices of the stomach. 



There is a good deal in the chemistry of bread-making ; and our 

 bread might be much improved if bakers had a more intelligent under- 

 standing of the science involved in their business ; for, although several 

 improvements have been introduced of late years, the most of our bread 

 is still prepared in the old fashion. The necessary quantity of flour is 



