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WHO IS LISTENING TO THE LECTURE?
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- 15. ACCORDING TO THE LECTURE, WHAT CHANGES IN EDUCATION OCCURRED IN THE SECOND HALF OF THE TWENTIETH CENTURY
11. WHO IS LISTENING TO THE LECTURE?
12. WHAT DOES THE PROFESSOR SAY ABOUT AMERICAN SCHOOLS BEFORE THE LATE NINETEENTH CENTURY? 13. WHAT IS STATED IN THE LECTURE ABOUT TEACHERS IN THE EARLY TWENTIETH CENTURY? 14. WHAT DID THE RULES FOR TEACHERS DISCUSSED IN THE LECTURE CONCERN? 15. ACCORDING TO THE LECTURE, WHAT CHANGES IN EDUCATION OCCURRED IN THE SECOND HALF OF THE TWENTIETH CENTURY? 16. WHAT DOES THE PROFESSOR SUGGEST PARENTS WILL EXPECT FROM TEACHERS IN THE TWENTY-FIRST CENTURY? PASSAGE FOUR Page 162 [ mp3 027-028] LPREP IBT 3 E AudioScript 18 Questions 17 through 22. Listen to part of a discussion in a geology class. (Professor) OK. So, now we’re going to move on to how to distinguish between two other minerals: gold and fool’s gold. So, first of all, you’re not going to find that mineral listed under the name fool’s gold in the mineral index, are you? Then, does anyone happen to know the real name of fool’s gold? ... No? OK, the name is iron pyrite, but I’ll bet you do know the reason it’s called fool’s gold. Anyone? (Student 1) I think it’s called fool’s gold because it can look sort of like gold, and sometimes people who found iron pyrite thought they’d found gold. (Professor) That’s right. So, you said that iron pyrite kind of looks like gold, but what exactly does that mean? (Student 1) It can be a shiny golden color, just like gold. (Professor) Good. So obviously you won’t always be able to tell them apart by color. Now, here are some pictures of the two minerals. If I tell you that the crystals of gold and iron pyrite have a different shape, um, that iron pyrite crystals are cubical, while those of gold are not, could you tell me which picture is iron pyrite? (Student 2) The one on the right must be iron pyrite, because the mineral on the right is kind of like lumps of metal crystals…like little tiny cubes (Professor) Yes! Now look at the picture of gold. It’s all in little nuggets and irregular shapes. It looks like a liquid that was frozen into a shapeless, messy form. Which it actually is. Alright, then. We can’t really tell the difference between them from the color. The crystal shapes are different, but that might be kind of hard to see with the naked eye if you only had a very small piece. And, as a matter of fact, I’d imagine that’s why people mixed them up. They were probably handling pretty tiny amounts. Ah … so what are some other ways you can tell them apart? Well, gold is an element, and fool’s gold is a compound of iron and sulfur … uh, actually iron sulfide. You have a question? (Student 1) Yes … um, why is it called iron pyrite if it’s made of iron and sulfur? And I’m pretty sure that there’s no element called pyrite. (Professor) Well, the answer is that the word pyrite is not the name of an element, but instead it came from the Greek word for fire. Here’s the thing; if you hit iron pyrite with metal, then it makes sparks. Some ancient cultures used to use iron pyrite to start fires, in fact. (Student 2) Excuse me, professor, but is that the way the differences are tested in a lab? (Professor) Good question. Well, the fact that fool’s gold is a compound of two elements, iron and sulfur, means that it has a very strong reaction to heat. When it’s heated, it turns black and smokes, and it develops a strong, uh, an awful odor. That’s the sulfur coming off of it. On the other hand, when you heat gold, nothing happens unless you get it so hot it melts. (Student 1) Are there any other differences? (Professor) Well, another identifying characteristic of gold is its softness. You can scratch it with almost anything … and if you hit it, it kind of flattens out. If you hit fool’s gold, though, it breaks apart into its little cubical crystals, and it’s much harder to scratch. This is why you always see people biting gold in the old Western cowboy movies. If it’s pure gold, it will be soft enough for your teeth to leave a mark. But don’t try that with iron pyrite. LPREP IBT 3 E AudioScript 19 Alright then. We have reaction to heat and softness, which can both be tested. Um another thing that, um … differentiates the two minerals is density. In equal amounts … uh, I mean given the same volume, true gold is denser than fool’s gold. If you have the same volume of gold and fool’s gold, the gold will weigh much more. I mean, it’ll have more mass. So, these are all things you could test in the lab, and I hate to disappoint you, but I’m afraid that you won’t be provided with a nugget of pure gold to do tests on. You will, though, be testing these properties on other minerals in the lab later on. OK, one or two more examples of some interesting minerals and we’ll call it an afternoon. Download 0.63 Mb. Do'stlaringiz bilan baham: |
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