it flexible.

542. When you pour nitric acid on copper filings, there is a
bubbling up of gas.

543. The flask or dish in which the action takes place becomes
very hot.

544. The copper disappears and a clear green solution is left.

545. In making cream of tomato soup, soda is added to the
tomatoes before the milk is, so that the milk will not curdle
How does the soda prevent curdling?

546. The soda makes the soup froth up.

547. A wagon squeaks when an axle needs greasing.

548. Seidlitz powders are mixed in only _half_ a glass of
water.

549. The work of developing photographs is all done with a
ruby light for illumination.

550. Coal slides forward off the shovel into a furnace when
you stop the shovel at the furnace door.

CHAPTER TWELVE

ANALYSIS

SECTION 58. _Analysis._

How can people tell what things are made of?

If it were not for chemical analysis, most of the big factories would
have to shut down, much of our agricultural experimentation would
stop, the Pure Food Law would be impossible to enforce, mining would
be paralyzed, and the science of chemistry would almost vanish.

Analysis is finding out what things are made of. In order to make
steel from ore, the ore has to be analyzed; and factories could not
run very well without steel. In order to test soil, to test cow's
milk, or to find the food value of different kinds of feed, analysis
is essential. As to the Pure Food Law, how could the government find
out that a firm was using artificial coloring matter or preservatives
if there were no way of analyzing the food? In mining, the ore must be
assayed; that is, it must be analyzed to show what part of it is gold,
for instance, and what part consists of other minerals. Also, the
analysis must show what these substances are, so that they can be
treated properly. And the science of chemistry is largely the science
of analyzing--finding out what things are made of and how they will
act on each other.

The subject of chemical analysis is extremely important. But in this
course it is impossible and unnecessary for you to learn to analyze
everything; the main thing is for you to know what analysis is and to
have a general notion of how a chemist analyzes things.

[Illustration: FIG. 186. The platinum loop used in making the borax
bead test.]

When you tested a number of substances with litmus paper to find out