CHAPTER IV

THE STATES OF MATTER

40. Evaporation. Place about 1 cc. of ether or of chloroform on a watch crystal and blow upon the surface of the liquid. Why does it evaporate so fast? Do you notice any change in the temperature of the watch glass? Why is this?

41. Boiling point. Pour about 250 cc. of distilled water into a suitable flask or beaker, and heat it at such a rate that the temperature rises slowly but steadily. Use a thermometer to keep the water stirred. At what temperature do you observe bubbles? Where do they appear to form? What are they? At about what temperature do larger bubbles begin to form at the bottom of the vessel? What becomes of them? Why? At what temperature do they move freely up through the liquid to the surface? Do they get larger or smaller as they rise? Why? When the water is gently boiling, try increasing the heat. Is the boiling any more energetic? Does the temperature rise any? How do you define the boiling point?

42. Freezing point; melting point. a. Powder about 3 g. of sulfur and place it in a small test tube. Heat it very slowly a little above a small Bunsen flame, stirring it with a thermometer. At what temperature does the sulfur begin to melt? During the process of melting watch the thermometer closely. Does the temperature change during the process? When all the sulfur has melted, remove the flame and let the sulfur cool. At what temperature does it begin to solidify? Does the temperature change during solidification?

b. Repeat the whole experiment with a little paraffin. Do you notice any differences? To the melted paraffin add a little vaseline. How does this affect the melting point of the paraffin?

c. If the salts are available, determine the melting point of crystallized calcium nitrate, crystallized sodium acetate, crystallized sodium thiosulfate.

43. Sublimation. Place 2 or 3 g. of ammonium chloride in a small evaporating-dish and warm it gently. Does it melt? What change do you notice? Cover the dish with a small inverted funnel and continue to heat very gently so that not too much smoke issues from the stem of the funnel. After a time let the dish cool. Is there any solid upon the sides of the funnel? How did it get there? What is such a process called?

CHAPTER V

THE LAWS OF CHEMICAL COMBINATION

I. THE LAW OF DEFINITE COMPOSITION

44. Determination of the weight of oxygen which combines with a definite weight of magnesium. a. Thoroughly clean and dry the porcelain crucible and lid included in your list of apparatus and weigh them accurately. Obtain a piece of magnesium ribbon weighing not to exceed 0.5 g. and scrape it with a knife until the surface is bright. Cut the ribbon into pieces 1 or 2 cm. in length, place the pieces in the crucible, and again weigh. Now place the covered crucible on the triangle and apply a gradually increasing heat. Magnesium burns violently when freely exposed to the air, hence the cover should be left on the crucible until the oxidation is nearly complete. This will require about twenty minutes. Cautiously remove the cover by means of the forceps, but hold it just above the crucible so that it can be returned at once in case the magnesium should begin to burn. Continue the heating until the substance no longer glows when the cover is removed. Finally, tip the crucible partly on its side, so as to give free access of air, and apply a strong heat for a few minutes longer. Withdraw the flame and reweigh the crucible, first allowing it to cool.

b. From your results calculate the weight of oxygen which combines with 1g. of magnesium. Repeat the experiment, using a different weight of magnesium. In case the time is not sufficient to repeat the experiment, compare your result with those obtained by other members of the class. Are they in accord with the law of definite composition? If not, how do you account for their variation from the law?