rnace is that
the temperature can be regulated to any desired intensity.

EXERCISES

1. Why does charcoal usually burn with no flame? How do you account for
the flame sometimes observed when it burns?

2. How do you account for the fact that a candle burns with a flame?

3. What two properties must the mantle used in the Welsbach lamp
possess?

4. (a) In what respects does the use of the Welsbach mantle resemble
that of lime in the calcium light? (b) If the mantle were made of
carbon, would it serve the same purpose?

5. Would anthracite coal be suitable for the manufacture of coal gas?

6. How could you prove the formation of carbon dioxide and water in the
combustion of illuminating gases?

7. Suggest a probable way in which natural gas has been formed.

8. Coal frequently contains a sulphide of iron. (a) What two sulphur
compounds are likely to be formed when gas is made from such coal? (b)
Suggest some suitable method for the removal of these compounds.

9. Why does the use of the bellows on the blacksmith's forge cause a
more intense heat?

10. What volume of oxygen is necessary to burn 100 l. of marsh gas and
what volume of carbon dioxide would be formed, all of the gases being
measured under standard conditions?

11. Suppose a cubic meter of Pennsylvania natural gas, measured under
standard conditions, were to be burned. How much water by weight would
result?

CHAPTER XIX

MOLECULAR WEIGHTS, ATOMIC WEIGHTS, FORMULAS

~Introduction.~ In the chapter on The Atomic Theory, it was shown that if
it were true that two elements uniting to form a compound always
combined in the ratio of one atom of one element to one atom of the
other element, it would be a very easy matter to decide upon figures
which would represent the relative weights of the different atoms. It
would only be necessary to select some one element as a standard and
determine the weight of every element which combines with a definite
weight (say 1 g.) of the standard element. The figures so obtained would
evidently represent the relative weights of the atoms.

But the law of multiple proportion at once reminds us that two elements
may unite in several proportions; and there is no simple way to
determine the number of atoms present in the molecule of any compound.
Consequently the problem of deciding upon the relative atomic weights is
not an easy one. To the solution of this problem we must now turn.

~Dalton's method of de