the oxygen begins to be given off. Fill three or four bottles with water, cover each with a piece of glass or cardboard, and invert the first one over the mouth of the delivery tube, removing the cover when the mouth is under water. Continue to heat the mixture until the bottle is full of oxygen, then cover it under water with the glass plate or cardboard, and stand it right side up on the table. In the same way fill as many jars as are needed for the experiments with oxygen. (Fig. 1.) FIG. 1.- Preparation of oxygen. Prepare several bottles of oxygen as directed and allow them to stand until all fumes have settled, before answering the following questions. 1. Examine a bottle of oxygen. a. State what you have done. b. Do you find oxygen to be a solid, a liquid, or a gas? c. State whether or not oxygen has color. 2. Heat some charcoal (carbon) till it glows and thrust it into a bottle of oxygen. a. Tell what was done and describe what happens. b. Does carbon burn better in air (which is a mixture of oxygen and other gases) or in pure oxygen? 3. State the three characteristics of oxygen which you have learned. 11. Carbon dioxid (formula, CO2). Laboratory Study No. 3. Demonstration. Preparation of carbon dioxid: Into a flask put some pieces of marble, and insert a stopper through which passes a thistle FIG. 2. 00000000000 Preparation of carbon dioxid or of hydrogen. tube and a delivery tube like that used in the preparation of oxygen. Pour into the thistle tube diluted hydrochloric acid until the lower end of this tube is covered. Collect a bottle of carbon dioxid in the same way that oxygen is collected, keeping the mouth of the bottle closed with a glass plate or cardboard. (Fig. 2.) Prepare a bottle of carbon dioxid as directed, and allow it to stand till all fumes have disappeared, before answering the following questions. 1. Examine a bottle of carbon dioxid and state whether it is a solid, a liquid, or a gas. Compare this gas and oxygen as to color. 2. Light a splinter of wood and thrust it into the bottle of carbon dioxid. a. Tell what was done and describe the effect of the carbon dioxid upon the burning splinter. b. How was the burning splinter or carbon affected by oxygen? 3. Generate some carbon dioxid as suggested above and pass it through the delivery tube into a test tube of clear lime water. Tell what was done and describe the effect of carbon dioxid on lime water. (Carbon dioxid is the only gas that affects lime water in this way; hence the latter is a reliable test for carbon dioxid.) 4. State the four characteristics of carbon dioxid which you have learned from these experiments. 5. Place in a bottle of pure oxygen a piece of glowing carbon, and allow it to burn as long as it will. When the carbon ceases to burn, quickly remove it, and pour in some clear lime water, cork the bottle, and shake. a. Tell what was done and describe the change that takes place in the lime water. b. What substance is evidently formed when carbon burns in oxygen? 6. When carbon is burned in oxygen, the two unite to form a new substance entirely different from either carbon or oxygen. This new substance is called carbon dioxid, because it is composed of one part of carbon and two of oxgyen. a. State the composition of carbon dioxid. b. Describe the method by which carbon dioxid was produced in 5, above. 7. (Optional.) By means of a glass tube blow the breath from the lungs into a test tube of lime water. a. Describe this experiment and the change in the lime water. b. What do you therefore conclude to be contained in the breath from the lungs? 12. Hydrogen (symbol, H) and water (formula, H2O). — Laboratory Study No. 4. Demonstration. Preparation of hydrogen (see Caution below): Into a flask put some pieces of zinc. (See Fig. 2.) Insert a stopper with two holes. Through one of the holes pass the lower end of a thistle tube until it nearly touches the bottom of the test tube, and through the other run a short piece of glass tubing. To the upper end of the latter attach by means of a piece of rubber tubing a delivery tube that will reach beneath the surface of a tray of water such as that used in collecting oxygen and in the preparation of carbon dioxid. Pour through the thistle tube enough diluted hydrochloric acid to cover the lower end of the thistle tube. (If hydrogen does not come off rapidly enough, put into the flask a bit of copper sulphate.) After the hydrogen has been given off for several minutes, collect a bottle over water in the same manner as in the oxygen experiment. Remove the bottle, holding it upside down, and place it on the desk in this position. Allow the bottle to stand till fumes disappear. Caution: If in 3 below an explosion occurs, collect another bottle of hydrogen before answering the questions, for an explosion indicates that oxygen is mixed with the hydrogen, and such a mixture is dangerous to experiment with. 1. Examine a bottle of hydrogen, and state whether hydrogen is a solid, a liquid, or a gas. Compare its color with that of oxygen and carbon dioxid. 2. Thrust a lighted stick up into the mouth of an inverted bottle of hydrogen. (This experiment will be more satisfactory if the room is darkened.) a. State what was done and tell how the hydrogen affected the burning stick. b. How does the burning stick affect the hydrogen? c. What is one difference between oxygen and hydrogen? d. What is one difference between hydrogen and carbon dioxid? 3. If hydrogen is not being given off from the delivery tube in sufficient quantity, pour into the thistle tube some hydrochloric acid. Detach the delivery tube from the rubber tube of the hydrogen apparatus and insert in its place a piece of glass tubing, the upper end of which is drawn out to a small diameter. Collect some of the gas in a test tube by displacement of air and light it. When it burns with only a slight puff, apply a lighted match to the hydrogen escaping from the drawn-out tube. Hold over the flame a bottle which is clean and dry. c. What, therefore, is formed when hydrogen burns? 4. When hydrogen burns, it unites with the oxygen of the air and forms oxid of hydrogen, more commonly known as water (formula, H2O). a. In what respect does hydrogen differ from oxid of hydrogen (water) in its most common form? b. State how oxid of hydrogen was formed. c. In what respects is the method of producing oxid of hydrogen (water) the same as that of producing oxide of carbon (carbon dioxid)? (See 11, 5 above.) 5. Name five characteristics of hydrogen. 13. Nitrogen (symbol, N) and the composition of the air. Laboratory Study No. 5. Demonstration. Fasten a candle to a piece of cardboard and float the latter on a tray of lime water. Light the candle, and cover the flame with an inverted wide-mouthed bottle, bringing the latter slowly down until the edge rests on the bottom of the tray. Allow the candle to burn as long as it will. Then turn the bottle right side up, covering the mouth with the cardboard, keeping inside the bottle the lime water that has risen to take the place of the oxygen. Shake the contents of the bottle, to make the lime water absorb the carbon dioxid, and allow it to stand till the upper part of the jar is clear. Keep the bottle covered to prevent the mixing of air with the nitrogen. 1. Examine a bottle of nitrogen. Is it a solid, a liquid, or a gas? What is its color? 2. Thrust a burning splinter of wood into the nitrogen. a. Tell what was done. Does the wood continue to burn? b. Does the nitrogen burn? c. In what respect does nitrogen differ from oxygen? 3. State four characteristics of nitrogen. 4. Why does carbon burn faster in oxygen than in air? 5. Air consists principally of oxygen and nitrogen. The water in the bottle represents the amount of oxygen there was in the bottle of air, and the nitrogen occupies the rest of the space. a. About what fractional part of the air in the bottle was oxygen? b. What fractional part of the air in the bottle is nitrogen ? 6. Expose to the air of the room for a half hour or more a dish with some clear lime water. a. Describe the experiment, stating the effect on the lime water. b. What substance does this experiment prove to be present in air? |