Page:Popular Science Monthly Volume 45.djvu/736

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THE POPULAR SCIENCE MONTHLY.

dium burns with intense brilliancy in gaseous oxygen, but in liquid oxygen would not burn at all, the very low temperature (-180º) hindering chemical action. Liquid oxygen has an electrical resistance five or six times greater than that of the gas, which itself is strongly magnetic. Put under the poles of an electromagnet, the liquid leaped up to them when the current was passed, and a little piece of cotton wool saturated with it was strongly attracted. Ordinary air from the room was liquefied in the presence of the audience. A small tube of liquid oxygen, placed in a vessel of air, was put under the air pump, and in a short time liquid air began to condense on its surface. Although the nitrogen and oxygen of the atmosphere are liquefied simultaneously, yet nitrogen, being the more volatile, boils off first, and leaves liquid oxygen behind. This can be proved by holding a glowing taper over a vessel of liquid air; it does not burst into flame until about four fifths of the contents have evaporated. Liquid air is magnetic, but more feebly so than liquid oxygen. It is also blue, and the absorption bands in its spectrum are less dark.

 

Bohemian Graphite.—Natural graphite occurs usually in masses and veins in the oldest rocks, like granite, gneiss, mica schist, and porphyry. At Schwarzbach, in Bohemia, it is found in irregular masses in the gneiss, apparently brought there after the formation of the rock, and having been substituted for the mica, of which it in some places takes the foliated texture. Schwarzbach is situated on a grassy plain among the wild mountains of southern Bohemia, in the district of Krunian. The mines and surrounding country belong to the immense domains of the Prince of Schwarzenberg. The mines employ eight hundred workmen, and produce from six thousand to ten thousand tons a year. The graphite is mined in shafts sunk one hundred metres or more beneath the surface of the ground. Being impregnated with water, it is easily broken into small blocks by the pick. It is sorted by the miner into first and second choice—prima and raffinade. These piles are again sorted, a different process being observed with either kind. The prima, which is designed for pencil-making, is sorted by hand, and all impurities and hard particles are removed from it. The raffinade is passed under millstones where a current of water passing carries off all the richest parts, and, giving up the sand and pyrites in a series of pans provided for them, carries the purified graphite into another series of pans. If pyrite is present in considerable proportions, it is burned out by passing the matter in gratings over flame.

 

The Waganda.—Describing Uganda in the British Association, Captain Williams said that whatever the merits of the country, the people were worth keeping, for they were a wonderful race. The missionaries had done great good, notwithstanding the conflict of religions. The men were fine, well built, and athletic, and the women were active and intelligent. They were not universally black—indeed, in Central Africa there was a considerable variety of shades. They had a strange theory of transmigration of souls, which prevented the people from utilizing the food supply that lay before them. The people were simply dressed; the women were not allowed to wear white cloth, while the men wore white if they could get it. They wore "bark cloth," which was stretched out on pegs to the right length. The Waganda were polygamists, each man having seven wives. The women were very happy, and did the hoeing and other agricultural work, while the men built the houses and carried the food. A man as a rule bought his wives. In one case he met a man who had bought a wife for four cows. He had paid two of the cows and then the lady was eaten by a leopard. He thought it was very hard lines that he should be compelled to pay the remaining cows. The houses were, as a rule, mere slight, temporary structures, but the house in which the late King Mtesa was buried was a wonderful structure with twenty feet or more of thickness of thatch. The churches—both Catholic and Protestant—were extremely fine, but the former had unfortunately been burned. The cruelties of the people had been much exaggerated, and were not comparable to the atrocities which were once committed. In former days a king had all the people killed who passed along a certain road from morning to night, and a man's life was almost worthless. The