The stopcock B is then opened and the heat withdrawn. Insert the values in the following table:

It is evident that the volume of the air in E must be equal to the volume occupied by the vapor formed by the chloroform, provided that the vapor is measured under the conditions of temperature and pressure to which the air in the tube is subjected. Knowing, therefore, the weight of the chloroform taken and the volume of vapor formed under definite conditions, it is easy to calculate the weight of 22.4 liters of the vapor under standard conditions.

By analysis it is possible to show that chloroform has the following composition: carbon, 10.04 per cent; hydrogen, 0.84 per cent; chlorine, 89.12 per cent. From your results determine the formula of chloroform. Why is it necessary to know the molecular weight in order to determine the formula?

Notes and queries. The stopper of the little bottle F containing the chloroform is loosened before dropping the bottle into the tube, in order that the vapor of the chloroform may easily escape. In performing the experiment the heat must be applied uniformly until the experiment is completed (why?); hence the flame should be protected from drafts of air. The amount of chloroform introduced must be small (about 0.13 g.); otherwise the volume of the vapor will be so large that the tube E will not hold the displaced air. Could other liquids be substituted for water in the outer tube? Before performing the experiment the tube A must be perfectly dry (why ?). To remove any vapor, insert a long, narrow glass tube and force a current of dry air through the tube, at the same time applying a gentle heat. Before measuring the volume of the air in E, bring the water within the tube to the level of the water outside, if necessary transferring the tube to a deep cylinder to accomplish this.

CHAPTER XXI

SOME HYDROCARBONS

121. Methane. a. Weigh out approximately 10 g. of fused sodium acetate and double that weight of soda lime (a mixture of calcium oxide and sodium hydroxide). Grind the two together in a mortar and put the mixture in a hard-glass test tube furnished with a stopper and a delivery tube (the oxygen generator of § 15). Support the tube with a clamp and heat gently, gradually increasing the heat. After the air has been expelled from the apparatus, collect two or three bottles of the gas over water.

b. Note the color, odor, and solubility of the gas. Hold a lighted match to the bubbles as they escape from the water. Pour a little bromine water into one of the bottles, place a stopper in the bottle, and shake vigorously. Is the color of the bromine changed? Set fire to the gas in the second bottle and, after it has burned, test the residual gas for the presence of carbon dioxide. Half fill a bottle with methane and then displace the remaining water with air. Quickly bring the mouth of the bottle over a flame. What connection is there between this experiment and a mine explosion?

122. Ethylene. a. Arrange a 250-cc. generating-flask on a sand bath and connect it with a gas-washing bottle containing dilute sodium hydroxide and provided with a delivery tube for collecting over water. Pour 10 cc. of alcohol very slowly into 60 cc. of concentrated sulfuric acid, stirring constantly during the mixing; pour the mixture into the generatingflask and insert the stopper. Carefully heat the mixture until there is a steady evolution of gas. If the heating is too rapid or the temperature reached is too high, the mixture may foam

badly and the alcohol be carbonized. Remembering that some free carbon is usually formed in the reaction, what gases other than ethylene would you expect to be formed? How would these act with sodium hydroxide in the wash bottle?

b. Collect two bottles of the gas and test its combustibility and its conduct towards bromine water. How does it compare with methane?

123. Acetylene. a. With your pliers pick up a small piece of calcium carbide and quickly insert it under the mouth of a test tube filled with water and inverted in a beaker of water. What action takes place? Test the reaction of the water with litmus paper. Holding the test tube in an inverted position (why ?), remove it from the water and quickly ignite the gas at the mouth of the tube. How does the flame compare with that of burning ethylene and burning methane?

b. Collect another test tube full of the gas, quickly pour into it about 1 cc. of bromine water, close the mouth of the tube with the thumb, and shake it vigorously. Is the bromine absorbed by the acetylene?

124. Iodoform. Pour 2 or 3 cc. of a solution of sodium hydroxide into a test tube, add a crystal or two of iodine, and then a few drops of alcohol. Warm slightly and observe the changes which occur. What color does the solution become? Is there a precipitate? What do you notice in regard to the odor? The product is iodoform (CHI), and its formation may be used as a good test for alcohol (though some other substances, when treated with iodine and an alkali, also give iodoform).