CHEMISTRY.
P. 169.—The formula (N₂O₂) shows that two atoms of nitrogen have united with two atoms of oxygen to form a molecule of nitrogen di-oxide. The formula Cu (NO₃)₂ shows that one atom of copper has united with two molecules, each composed of one atom of nitrogen and three atoms of oxygen, to form one molecule of cupric nitrate. In like manner Fe₂ (NO₃)₆ indicates that two atoms of iron have united with six molecules, each composed of one atom of nitrogen and three atoms of oxygen, to form one molecule of ferric nitrate.
P. 173.—“Refractive power” of water. When a ray of light strikes the surface of a new medium, a portion of it is turned out of its original course or refracted. This gives rise to some well-known effects. When any object is placed in water and viewed obliquely it looks to be nearer the surface than it is, because the light in passing from the denser medium takes a direction more inclined to the horizontal, and an object always appears directly in line with the ray of light entering the eye.
P. 178.—“Crécy,” kresˈse. This battle took place August 26, 1346, between the English under Edward III. and the French under Philip VI. It is said that Edward had six pieces of artillery. Artillery had probably not been used in the field before this time.
P. 182.—“Trinˌi-tro-cĕlˈlu-lose.”
P. 185.—“Mont Cenis,” mōⁿᵍ sŭh-nē. This tunnel under the Alps is in reality some sixteen miles from Mont Cenis, whose name it bears. The first mine was fired in 1857, and for four years the piercing was done by hand; the need of a quicker method led to the invention of a machine drill—a perforating machine worked by compressed air. The work was carried on by day and night, from both sides of the mountains, until the two bodies of workmen met, December 26, 1870. The tunnel was opened for railway travel September 17, 1871. Its length is nearly eight miles, and the cost of the tunnel was $15,000,000.
“St. Gotˈhard.” This tunnel is also through the Alps. The length is nine and one fourth miles. Its construction was begun in 1872, and it was completed in eight years.
P. 189.—“Phosphorus ne-croˈsis.” The latter term is derived from a Greek word, meaning to make dead, to mortify, and is a disease which attacks bony tissues, as gangrene effects the soft parts. “The acid fumes thrown off from phosphorus in the various processes of making matches, frequently cause among the people employed a terrible disease, which attacks the teeth and jaws.… Its natural course is to rot the entire jaw bone away.”
P. 190.—“Al-lŏtˈro-pĭsm.” Dana says allotropism is “the property of existing in two or more conditions which are distinct in their physical or chemical relations. Thus, carbon occurs crystallized in octahedron, and other related forms, in a state of extreme hardness, in the diamond; it occurs in hexagonal forms, and of little hardness, in black lead; and again occurs in a third form, with entire softness, in lamp-black and charcoal. In some cases one of these is peculiarly an active state, and the others a passive one. Thus, ozone is an active state of oxygen, and is distinct from ordinary oxygen, which is the element in its passive state.”
P. 194.—“Chemicking,” kemˈik-ing.
P. 203.—Translation of French sentence: “This last virtue I believe it still to possess, if the husband is rich enough to buy the jewel which his wife is ambitious to own.”
P. 217.—“Boussingault,” booˌsănˈgoˌ; Jean Baptiste. A noted French chemist of this century.