英文科學(xué)讀本 第六冊(cè)·Lesson 37 Sulphur

Lesson 37 Sulphur

I have this morning another common, well-known substance to talk to you about, said Mr. Wilson, as he showed the class a piece of roll-brimstone. "A very simple examination of this substance, which is known indiscriminately as sulphur—or brimstone—will tell you that it is a solid body, of a lemon-yellow color, and that it has a faint odor but no taste.

If we tap it with a hammer we shall learn that it is very brittle; and if we put it into water we shall prove that it is insoluble in water. We can, however, dissolve it in oil of turpentine. It takes fire when a light is applied to it, showing that it is highly inflammable, and it burns with a peculiar pale-blue flame and a suffocating odor. Now let us have an experiment. I will put some crushed sulphur in a test-tube and heat it gently over the Bunsen burner. The solid substance changes at first into a clear, yellow, limpid liquid, but as the heat is continued it becomes darker in color, and of the consistency of treacle; and finally it boils and passes off as vapor. While it is boiling we will introduce a small coil of fine copper wire into the mouth of the tube. The metal at once takes fire in the sulphur-vapor, and burns with brilliant effect. Now think of the combustion of bodies in oxygen and also in chlorine. You remember, of course, that we call the compounds formed by the burning—in the one case oxides, in the other chlorides.

Our last experiment showed us the copper taking fire and burning in a similar way in the sulphur-vapor. The product formed by that burning is known as sulphide of copper. Most of the metals combine with sulphur to form sulphides. Indeed, most of the metallic ores are sulphides. Copper and iron pyrites, two common forms of the ores of these metals, are really sulphides. Sulphur is also met with in combination with mercury, forming a sulphide commonly called cinnabar. This is the chief source whence we obtain that useful metal. In one of our early lessons the method of separating the mercury from the ore was described. Most of the sulphur of commerce is obtained in the free state—that is, uncombined with other substances— from volcanic districts such as Sicily, Southern Italy, Iceland, and Mexico.

Sulphur is frequently met with in the waters of mineral springs. The waters of Harrogate owe their medicinal value to the sulphur which they contain. The roll-sulphur which I showed you first is obtained by pouring the melted sulphur into wooden molds and allowing it to cool.

The flowers of sulphur are formed by boiling ordinary sulphur, and causing the vapor from the boiling liquid to pass into a cold chamber, where it condenses, and settles upon walls and floor as a fine powder. Sulphur is largely employed in the manufacture of gunpowder and matches, and for many other purposes.

I have now another experiment to show you. I will put a piece of sulphur in the deflagrating spoon, set it on fire by applying a red-hot wire to it, and lower it into this jar of oxygen which I have in readiness. The sulphur immediately bursts into a brilliant purple-blue flame, giving out intense heat, and the product of the burning is a suffocating gas. This gas is an oxide of sulphur. We call it sulphur dioxide. I will next pour some blue litmus infusion into the jar containing the sulphur dioxide, close the jar with my hand, and shake it up.

Now, without removing my hand, I will invert the vessel in this bowl of water, and if the hand be then taken away, the water will rush up into the jar with great violence, and the blue litmus coloring-matter will change to a bright red. Sulphur dioxide is so soluble that water will dissolve nearly fifty times its volume of this gas. This is why the water rushed up into the bottle.

If you dip your finger into the solution and put it to your tongue you will find that this dissolved oxide has a sour taste.