bats. The accompanying half-tones, from photographs by Professor A. W. Gamble, of the Logansport High School, give an excellent idea of places of interest near the schoolhouse. The region around is covered with drift, in some places so thin that vegetation completely dries up if rain does not fall at least once a week; generally, however, the drift is fifty feet and upward in thickness and forms a very fertile soil; in a few places the bed-rock crops out entirely above the drift. We listened recently to a former teacher in this district, who described a series of general noon-day lessons which lasted for a term of four months. Ten minutes were given to each lesson. From the drift the teacher had collected feldspar, quartz, granite, gneiss, hornblende, and sandstone. The pupils were all first taught to distinguish between all these rocks and the limestone by (test 1) color and general appearance. They were shown that they (test 2) could scratch the limestone with a knife but not any of the other rocks. The gneiss and sandstone would sometimes crumble before the knife but the separate pieces were hard. Some of the limestone was then treated in a test-tube with weak hydrochloric acid-one part of the acid to four of water, * and (test 3) it vigorously effervesced. None of the other stones would do this. The teacher then heated a small piece of limestone very hot in a blow-pipe flame, and after it had cooled, placed it on a piece of red litmus paper and wet it with a drop Later, when the limestone tests had become familiar and this experiment was being reviewed, the teacher decanted some of the escaping gas into limewater and showed that it turns the limewater milky. He breathed into limewater and showed that the same result follows. The breath contains the same gas that the stone yields when treated with acid, carbon dioxide. This gas, the teacher explained, collects in cisterns, wells, and caves sometimes, especially caves in volcanic districts, and he told the story of the Upas Tree of Java, and the real cause of its seemingly deadly influence. toothed spar is also limestone. A fine sample of nail-head spar was also found in a quarry near by, and shown also by the several tests to be limestone. It thus appears that the same mineral often crystallizes in several different forms. of water; the paper (test 4) turned blue. None of the other stones, however, would behave in this way. He then moistened a stick of the limestone at its tip with hydrochloric acid and put it in his blow-pipe flame and the flame turned (test 5) a fine red in color. The other stones when treated Several samples of marble were now in the same way yielded no red. brought to the school-house, some of it Every day these various tests for lime- black, some white, gray, reddish, balmoral stone were reviewed, and as often as necessary they were repeated before the children; and some of them were performed again and again by the children themselves. In a bluff near by, some crystals of Iceland spar were found, which, when placed over a dot on paper, made the dot appear double. The old tests were applied and the Iceland spar was shown to be limestone. The magic crystals became the wonder of the neighborhood. Some pieces of limestone were broken across, and cavities were found in them partially filled with crystals of dog-toothed spar. The familiar tests again showed that the dog and green. |