2. What essential constituent of the air is found in larger amount in manufacturing districts than in the open country?
3. Can you suggest any reason why the growth of clover in a field improves the soil?
4. Why are the inner walls of a Dewar bulb sometimes coated with a film of silver?
5. To what is the blue color of liquid air due? Does this color increase in intensity on standing?
6. When ice is placed in a vessel containing liquid air, the latter boils violently. Explain.
7. Taking the volumes of the oxygen and nitrogen in 100 volumes of air as 21 and 78 respectively, calculate the percentages of these elements present by weight.
8. Would combustion be more intense in liquid air than in the gaseous substance?
9. A tube containing calcium chloride was found to weigh 30.1293 g. A volume of air which weighed 15.2134 g. was passed through, after which the weight of the tube was found to be 30.3405 g. What was the percentage amount of moisture present in the air?
10. 10 l. of air measured at 20° and 740 mm. passed through lime water caused the precipitation of 0.0102 g. of CaCO3. Find the number of volumes of carbon dioxide in 10,000 volumes of the air.