[Specimen Page, No. 6.] CARBONIC ANHYDRIDE. 33 Sometimes carbonic anhydride is produced in wells, and, being so much heavier than air, it remains at the bottom. If a man goes down into such a well, he will have no difficulty at first, because the air is good; but when he is near the bottom, where the gas has accumulated, he will gasp for breath and fall; and if anyone, not understanding the cause of his trouble, goes down to assist him, he too will fall senseless, and both will quickly die. The way to ascertain whether carbonic anhydride has accumulated at the bottom of a well is to let a light down into it. If it goes out, or even burns very dimly, there is enough of the gas to make the descent perilous. A man going down a well should always take a candle with him, which he should hold a considerable distance below his mouth. If the light burns dimly, he should at once stop, before his mouth gets any lower and he takes some of the gas into his lungs. When this gas is in a well or pit, of course it must be expelled before a man can descend. There are several expedients for doing this. One is to let a bucket down frequently, turning it upside down, away from the mouth of the well, every time it is brought up, a plan which will remind you of the experiment represented in Fig. 24. But a better way is to let down a bundle of burning straw or shavings, so as to heat the gas. Now heated bodies expand, gases very much more than solids or liquids, and, in expanding, the weight of a certain volume, say of a gallon, becomes lessened. So that if we can heat the carbonic anhydride enough Fig. 25. to make a gallon of it weigh less than a gallon of air, it will rise out of the well just as hydrogen gas would do. Fig. 25 shows how you may perform this experiment upon a small scale. [EASY INTRODUCTION TO CHEMISTRY-See Page 13.1 [Specimen Page, No. 7.] For Latin Prose-Historical. DISASTROUS RETREAT OF THE ENGLISH FROM CABUL. IT 17 T took two days of disorder, suffering, and death to carry the army, now an army no more, to the jaws of the fatal pass. Akbar Khan, who appeared like the Greeks' dread marshal from the spirit-land at intervals upon the route, here demanded four fresh hostages. The demand was acquiesced in. Madly along the narrow defile crowded the undistinguishable host, whose diminished numbers were still too numerous for speed: on every side rang the war-cry of the barbarians: on every side plundered and butchered the mountaineers: on every side, palsied with fatigue, terror, and cold, the soldiers dropped down to rise no more. The next day, in spite of all remonstrance, the general halted his army, expecting in vain provisions from Akbar Khan. That day the ladies, the children, and the married officers were given up. The march was resumed. By the following night not more than one-fourth of the original number survived. Even the haste which might once have saved now added nothing to the chances of life. In the middle of the pass a barrier was prepared. There twelve officers died sword in hand. A handful of the bravest or the strongest only reached the further side alive as men hurry for life, they hurried on their way, but were surrounded and cut to pieces, all save a few that had yet escaped. Six officers better mounted or more fortunate than the rest, reached a spot within sixteen miles of the goal; but into the town itself rode painfully on a jaded steed, with the stump of a broken sword in his hand, but one. LIVY, xxi. c. 25, § 7-10. XXXV. c. 30. xxiii. c. 24. DEFEAT OF CHARLES THE BOLD AND MASSACRE OF HIS TROOPS AT MORAT. IN N such a predicament braver soldiers might well have ceased to struggle. The poor wretches, Italians and Savoyards, six thousand or more in number, threw away their arms and made [MATERIALS AND MODELS-See Page 16.] |