The Romance of Modern Chemistry

CHAPTER IV INVISIBLE SUBSTANCES, AND HOW WE KNOW OF THEIR EXISTENCE ° EEING is believing ” is a familiar proverb, but we must recognise that the saying does not contain all the truth about the relation of seeing to believing, and that we believe in many things which we cannot see. Even in the realm of matter, apart altogether from the realm of mind, there are some things the existence of which is not directly obvious by the evidence of our senses. The chemist, whose business it is to deal with all sorts and conditions of matter, knows many sub- stances—“gases,” he calls them—of which he could not say—“ There ! See, smell, touch, taste.'” A gas may be without smell or taste, it may be as intangible as a spirit, and as for seeing it, why, it may be off* and away while the observer still thinks he is looking at it. And yet it is possible to satisfy ourselves by some more or less indirect observations that these invisible, odourless, in- tangible, and tasteless substances do really exist. The chemist, at least, believes in the existence of gases such as oxygen, hydrogen, nitrogen, and carbon dioxide as firmly as he believes in the existence of iron, sulphur, turpentine, or water. It must be observed that the difficulty which is met with in the case of the four gases just mentioned does not occur with all gaseous substances. Some betray their 39