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120 when you have seen its power of changing ice into water and water into steam, you have seen the two principal results of the application of heat. I want you now to see how it expands all bodies—all bodies but one, and that under limited circumstances. Mr. Anderson will hold a lamp under that retort, and you will see the moment he does so that the air will issue abundantly from the neck, which is under water, because the heat which he applies to the air causes it to expand. And here is a brass rod (fig. 32) which goes through that hole, and fits also accurately into this gauge; but if I make it warm with this spirit-lamp, it will only go in the gauge or through the hole with difficulty; and if I were to put it into boiling-water, it would not go through at all. Again, as soon as the