Although the phlogiston theory was self-consistent, it was awkward because it required that imaginative, even mysterious, properties be ascribed to phlogiston. Phlogiston was elusive. No one had ever isolated it and experimentally determined its properties. At times it seemed to show a negative weight: the residue left after burning weighed more than the material before burning. This was true, for example, when magnesium burned. Sometimes phlogiston seemed to show a positive weight, when, for example, wood burned, the ash weighed less than the starting material. And since so little residue was left when alcohol, kerosene, or high-grade coal burned, these obviously different materials were thought to be pure or nearly pure phlogiston.

In the eighteenth century, Antoine Lavoisier, on the basis of careful experimentation, was led to propose a different theory of burning, one that required a constituent of air- later shown to be oxygen- for combustion. Since the weight of the oxygen is always added, the weight of the products of combustion, including the evolved gases, would always be greater than the weight of the starting material.

Lavoisier's interpretation was more reasonable and straightforward than that of the phlogiston theorists. The phlogiston theory, always clumsy, became suspect, eventually fell into scientific disrepute, and was replaced by new ideas.

1. What does the passage mainly discuss?

(A) The chemical composition of phlogiston.
(B) Attempts to explain what happens when materials burn.
(C) Limitations of seventeenth-century scientific theories.
(D) The characteristics of the residue left after fires.

2. The word "it" in line 4 refers to

(A) burning
(B) phlogiston
(C) combustible material
(D) air

3. The "phlogiston transfer" mentioned in line 5 is a term used to describe the

(A) natural limits on the total volume of phlogiston
(B) absence of phlogiston in combustible material
(C) ability of phlogiston to slow combustion
(D) release of phlogiston into the air from burning material

4. The word "properties" in line 10 is closest in meaning to

(A) interpretations
(B) locations
(C) characteristics
(D) virtues


5. The phrase "ascribed to" in line 10 is closest in meaning to

(A) analyzed and isolated in
(B) returned to their original condition in
(C) assumed to be true of
(D) diagrammed with

6. The author mentions magnesium in line 14 as an example of a substance that

(A) seemed to have phlogiston with a negative weight
(B) leaves no residue after burning
(C) was thought to be made of nearly pure phlogiston
(D)was thought to contain no phlogiston

7.The "different materials" mentioned in line 17 were considered different because they

(A) required more heat to burn than other substances did
(B) burned without leaving much residue
(C) were more mysterious than phlogiston
(D) contained limited amounts of phlogiston

8. The word "constituent" in line 19 is closest in meaning to

(A) component
(B) opposite
(C) principle
(D) temperature

9. The word "Since" in line 20 is closest in meaning to

(A) later
(B) because
(C) during
(D) although

10. Which of the following is true of both the phlogiston theory of burning and Lavoisier's theory of burning?

(A) Both theories propose that total weight always increases during burning.
(B) Both theories are considered to be reasonable and straightforward.
(C) Both theories have difficulty explaining why residue remains after burning.
(D)Both theories recognize that air is important to combustion.

Questions 11-22

Iron production was revolutionized in the early eighteenth century when coke was first used instead of charcoal for refining iron ore. Previously the poor quality of the iron had restricted its use in architecture to items such as chains and tie bars for supporting arches, vaults, and walls. With the improvement in refining ore, it was now possible to make cast-iron beams, columns, and girders. During the nineteenth century further advances were made, notably Bessemer's process for converting iron into steel, Which made the material more commercially viable.

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