Page:Popular Science Monthly Volume 25.djvu/653

Rh This adhesion is probably aided by an oozing out or efflorescence of the vapor held by the fibers, and its condensation on their surfaces. This point, be it understood, is merely hypothetical, as the efflorescence is not visible.

"When the stale bread is again heated, a general expansion occurs by the conversion of liquid water into aqueous vapor, every grain of water thus converted expanding to seventeen hundred times its former bulk. As this happens throughout, i.e., upon the surface of every one of the countless fibers or particles, there must be a general elbowing in the crowd, breaking up the recent adhesion between these fibers and drawing them all apart in the directions of least resistance, i.e., toward the open spaces of the larger and visible pores, producing that apparent diminution of porosity that I have observed as the visible characteristic of the change.

This explanation of the change may be further demonstrated by cutting a loaf through the middle from top to bottom, and exposing the cut surfaces. In this case the bread becomes unequally stale, more so near the cut surface than within. The unequal pull due to the greater adhesive approximation of the fibers and small particles causes a rupture of the exposed surface of the crumb, which becomes cracked or fissured without any perceptible alteration of the size of the visible pores. If the two broken faces be now accurately placed together, the halves thus closely joined, firmly tied together, and placed for an hour in the oven, it will be seen on separating them that the chasms are considerably closed, though not quite healed. Careful examination of the structure of the inside, by breaking out a portion of the crumb, will reveal that loosening of the structure which I have described.

I should add that, in quoting the figures given by Boussingault in my last, I inadvertently omitted to reduce them from the French to the English thermometric scale: 130° to 150° centigrade is equal to 266° to 302° Fahr., which is considerably below the temperature required for starting the original baking.

"Popped corn" is a peculiar example of starch-cookery. Here a certain degree of porosity is given to an originally close-compacted structure of starch by the simple operation of explosive violence due to the sudden conversion into vapor of the water naturally associated with the starch. The operation is too rapid for the production of much dextrin.

As most of my readers doubtless know, peas, beans, lentils, and other seeds of leguminous plants are more nutritious, theoretically, than the seeds of grasses, such as wheat, barley, oats, maize, etc. I was glad to see at the Health Exhibition a fine series of the South Kensington cases displaying in the simplest and most demonstrative manner the proximate analyses of the chief materials of animal and vegetable food. I refer to them now because they do not receive the attention they deserve. On the opening day there was, out of all the