Overview

Lesson Procedure

60-70 minutes of class time across 5 phases.

1. Warm-Up5 minutes
2. Direct Instruction15-20 minutes
3. Guided Practice15-20 minutes
4. Independent Practice20 minutes
5. Closure5 minutes

1. Warm-Up5 minutes

   Remind students of the tubes they set up two or three days ago in Activity 1, and show the modern table below. Tell them that people argued for centuries about what air is: Aristotle counted it as one of four elements, and in the 1700s many chemists explained burning with the phlogiston theory, which held that a burning substance gives off a substance called phlogiston into the air.

   Modern composition of dry air at sea level, percent by volume (standard reference values)

   Gas	Percent of dry air
   Nitrogen	78.08
   Oxygen	20.95
   Argon	0.93
   Carbon dioxide	about 0.04 (about 420 parts per million in 2024)
   Neon, helium and other gases	less than 0.01 in all

   Warm-Up Prompt

   If this table is right, what share of the air in your test tube should the rusting steel wool be able to use up, and what share should be left? What would it mean if your tube showed a very different number?

   Take answers. If rusting uses only oxygen, about a fifth of the air should go and about four fifths should stay. A very different result could mean the table is wrong, or, far more likely, that something in the experiment went differently. Say that this is today's skill: RST.9-10.9 asks them to compare and contrast findings in a text with those from other sources, including their own experiments, and to note when the findings support or contradict earlier explanations or accounts.

2. Direct Instruction15-20 minutes

   The routine. Post the four steps and keep them up. (1) State each finding as one sentence with its number, units and conditions. (2) Line up the findings on the same question; two findings can only be compared if they answer the same question. (3) Compare and contrast: say where the findings agree, where they differ and by how much, and look for a difference in method that could explain the gap. (4) Judge the earlier explanation or account: supported, contradicted or not tested, and how strongly. A finding supports an explanation when the explanation predicts it; it contradicts an explanation when the explanation predicts something else.

   Model with Lavoisier (T1). Antoine Lavoisier (1743-1794) was a French chemist whose experiments on burning and on the air helped to overturn the phlogiston theory. Show Diagram 1 and walk through his apparatus before reading: mercury is heated in a flask whose bent neck leads into a bell-shaped glass standing in a trough of mercury, so a fixed sample of air is trapped above the hot metal. Read T1 aloud. Mercury is toxic, and its vapor is dangerous to breathe: this experiment is shown only as a historical account and is never repeated in class.

   1I took a matrass (A, fig. 14. plate II.) of about 36 cubical inches capacity, having a long neck B C D E, of six or seven lines internal diameter, and having bent the neck as in Plate IV. Fig. 2. so as to allow of its being placed in the furnace M M N N, in such a manner that the extremity of its neck E might be inserted under a bell-glass F G, placed in a trough of quicksilver R R S S; I introduced four ounces of pure mercury into the matrass, and, by means of a syphon, exhausted the air in the receiver F G, so as to raise the quicksilver to L L, and I carefully marked the height at which it stood by pasting on a slip of paper. Having accurately noted the height of the thermometer and barometer, I lighted a fire in the furnace M M N N, which I kept up almost continually during twelve days, so as to keep the quicksilver always almost at its boiling point. Nothing remarkable took place during the first day: The Mercury, though not boiling, was continually evaporating, and covered the interior surface of the vessels with small drops, at first very minute, which gradually augmenting to a sufficient size, fell back into the mass at the bottom of the vessel. On the second day, small red particles began to appear on the surface of the mercury, which, during the four or five following days, gradually increased in size and number; after which they ceased to increase in either respect. At the end of twelve days, seeing that the calcination of the mercury did not at all increase, I extinguished the fire, and allowed the vessels to cool. The bulk of air in the body and neck of the matrass, and in the bell-glass, reduced to a medium of 28 inches of the barometer and 10 deg. (54.5 deg.) of the thermometer, at the commencement of the experiment was about 50 cubical inches. At the end of the experiment the remaining air, reduced to the same medium pressure and temperature, was only between 42 and 43 cubical inches; consequently it had lost about 1/6 of its bulk. Afterwards, having collected all the red particles, formed during the experiment, from the running mercury in which they floated, I found these to amount to 45 grains.

   2I was obliged to repeat this experiment several times, as it is difficult in one experiment both to preserve the whole air upon which we operate, and to collect the whole of the red particles, or calx of mercury, which is formed during the calcination. It will often happen in the sequel, that I shall, in this manner, give in one detail the results of two or three experiments of the same nature.

   3The air which remained after the calcination of the mercury in this experiment, and which was reduced to 5/6 of its former bulk, was no longer fit either for respiration or for combustion; animals being introduced into it were suffocated in a few seconds, and when a taper was plunged into it, it was extinguished as if it had been immersed into water.

   • Pulling out the finding (T1, paragraph 1)

     Lavoisier's first paragraph is mostly about equipment. What exactly did he find, and under what conditions did he measure it?

     Result: The finding is in the last sentences: the trapped air was "about 50 cubical inches" at the start and "only between 42 and 43 cubical inches" at the end, so it "had lost about 1/6 of its bulk," and 45 grains of red particles had formed. The condition that makes the numbers comparable is also stated: both volumes were "reduced to a medium of 28 inches of the barometer and 10 deg." of the thermometer, that is, corrected to the same pressure and temperature. Before comparing a finding with anything else, students write it as one sentence with its number and its conditions.

   • Comparing with a modern source (T1 and the modern table)

     Compare Lavoisier's finding with the modern composition of dry air. What do the two sources agree on, and where do they differ?

     Result: Compare: both sources show that only part of the air can be used up and that the rest will not keep a flame or an animal alive. Lavoisier's leftover air put out a taper "as if it had been immersed into water"; the modern table shows that the leftover is almost all nitrogen and argon, gases that do not support burning. Contrast: "about 1/6" is 100 ÷ 6 ≈ 16.7 percent, and 7 to 8 cubic inches out of 50 is 14 to 16 percent, while the modern oxygen share is 20.95 percent. Lavoisier's number is 4 to 7 percentage points low. Why it is low is a question to hold: T4 gives Lavoisier's own answer.

   Close the model by naming what students just did. They stated the finding with its conditions (step 1), lined it up with the modern table on the same question, "what share of the air can be used up?" (step 2), and compared and contrasted it (step 3). Step 4 comes next, with a second text.

3. Guided Practice15-20 minutes

   Pairs read Ramsay's account of Henry Cavendish (T2). Cavendish (1731-1810) was an English chemist and physicist; Ramsay (1852-1916) was a chemist who, with Lord Rayleigh, found argon in the air in 1894. Ramsay uses the phlogiston theory's names: "dephlogisticated air" is oxygen and "phlogisticated air" is nitrogen. Nitric oxide is a gas that combines with oxygen and dissolves in water, so it can remove the oxygen from a sample.

   1It was in 1777 that he commenced his beautiful “Experiments on Air,” the first account of which was published in 1783. They led to the discovery of the constant quantitative composition of the atmosphere, of the compound nature of water, and of the composition of nitric acid, and pointed the way to the recent discovery of argon.

   2In determining the composition of the atmosphere, Cavendish made use of nitric oxide in presence of water, as a means of removing oxygen. This process, originally devised by Mayow, was rediscovered by Priestley, who employed it to ascertain the “goodness” of various samples of air; in Cavendish’s hands it became an accurate quantitative method. The title of his paper, published in the Philosophical Transactions for 1783, is “Of a new Eudiometer.” The term “eudiometer,” signifying “measurer of goodness,” was devised when it was supposed that ordinary air presented considerable variations in its power of supporting respiration and combustion, according to the seasons, and according to the place from which it was collected. Dr. Ingenhousz had found a greater absorption when air from near the sea-coast was tested by Priestley’s method with nitric oxide, than when town-air was employed; and he ascribed the salubrious nature of sea-air to its being richer in “vital air.” The Abbé Fontana, too, had made similar experiments, and had come to similar conclusions. Cavendish modified Fontana’s apparatus, rendering it capable of giving more accurate results; and during the last half of the year 1781 he analysed the air collected on sixty days, some fine, some wet, and some foggy. He also collected air from different localities, sometimes at Marlborough Street, sometimes at Kensington, which was then a country village. The results of his analyses establish as the composition of air, freed from carbon dioxide by potash:

   379·16 per cent of phlogisticated air (nitrogen).
   20·84 per cent of dephlogisticated air (oxygen).

   4This result does not differ materially from those obtained by the best modern analyses, which give, within very small variations:

   579·04 per cent of nitrogen and argon,
   20·96 per cent of oxygen,

   6after absorption of carbon dioxide, ammonia, and water-vapour.

   Then groups read their own tubes from Activity 1 (Part 2, the reading) and add their numbers to a class table. Classes that could not run the experiment use the sample data sheet below, T3. Diagram 2 has an empty bar for the class result.

   1Question. When iron rusts in a closed pocket of air, how much of that air is used up? We tested this in class, two days after reading about Lavoisier's mercury experiment. The class and the data are invented for teaching; the method is a standard classroom one.

   2Method. Each of six groups pulled apart a 1 g pad of fine steel wool, soaked it in white vinegar for one minute to remove its oily coating, shook it, and pushed it to the closed end of a 20 cm test tube. We turned the tube upside down in a tall beaker of water, lowered it until about 5 cm of water stood inside, and clamped it. With a ruler we measured the air column, from the closed end to the water surface inside the tube. Before every reading we moved the tube up or down until the water inside and outside were at the same level, so that the trapped air was at room pressure. The room stayed at 21 °C for every reading.

   3Results. The length of the air column in each tube was:
   Group 1: 152 mm at the start, 123 mm after 3 days.
   Group 2: 148 mm at the start, 119 mm after 3 days.
   Group 3: 150 mm at the start, 121 mm after 3 days.
   Group 4: 155 mm at the start, 124 mm after 3 days.
   Group 5: 149 mm at the start, 136 mm after 3 days.
   Group 6: 151 mm at the start, 121 mm after 3 days.

   4Notes. Group 5 forgot to soak its steel wool in vinegar. Groups 1, 2 and 3 also read their tubes after 24 hours: 152 mm to 128 mm, 148 mm to 125 mm, and 150 mm to 126 mm. In every group except Group 5, the water level did not move between day 2 and day 3. The steel wool had turned orange-brown with rust.

   5Our conclusion. About one fifth of the air was used up by the rusting iron, and the air left in the tubes put out a burning splint when our teacher tested one tube. So air is about 20 percent oxygen, and Lavoisier was wrong.

   The results in T3 as a table (invented data): length of the air column in mm

   Group	At the start	After 24 hours	After 3 days
   1	152	128	123
   2	148	125	119
   3	150	126	121
   4	155	not read	124
   5	149	not read	136
   6	151	not read	121

   • A finding that contradicts an earlier account (T2)

     According to Ramsay, what did Ingenhousz and Fontana report about the air, and how do Cavendish's findings bear on their account?

     Result: The earlier account: Ingenhousz "had found a greater absorption" in sea-coast air than in town air and "ascribed the salubrious nature of sea-air to its being richer in 'vital air'"; Fontana came "to similar conclusions." Cavendish tested air "collected on sixty days, some fine, some wet, and some foggy," from a London street and from Kensington, with a more accurate instrument, and found one composition: 20.84 percent oxygen. His findings contradict the account that the share of oxygen changes from place to place or day to day. They do not test sea air directly, so the fairest wording is that they cast strong doubt on it.

   • Comparing your own experiment (T3, Group 1)

     Group 1's air column went from 152 mm to 123 mm. What share of the air was used up, and how does the method compare with Lavoisier's?

     Result: The tube has the same width all the way along, so the volume of air is proportional to the length of the column. Group 1 lost 152 - 123 = 29 mm, and 29 ÷ 152 ≈ 0.191, or about 19.1 percent. Compare the methods: both trap air over a liquid, let a metal take up part of it, and measure how much the trapped air shrinks. Contrast: Lavoisier heated mercury almost to boiling for twelve days, while the class let iron rust at 21 °C for three days, and the class corrected for pressure by leveling the water, while Lavoisier corrected his readings to a standard barometer and thermometer.

   Debrief with step 4: Does the class experiment support or contradict the phlogiston theory's claim that burning and rusting add something to the air? The air shrank instead of gaining anything, so the result fits Lavoisier's view that the metal takes something out of the air. Push students to word this carefully: one experiment contradicts the prediction, but a supporter of the theory in 1780 had ways to explain it away, which is why Lavoisier did more than measure the air (T4).

4. Independent Practice20 minutes

   Students read T4, the four paragraphs that follow T1 in Lavoisier's chapter, and answer quiz questions 1-20. Questions 1-6 and 15-17 use T4; questions 7-10 and 18 use the lab report T3; question 11 uses Diagram 2; questions 12 and 13 use T1; question 14 uses T2; and questions 19 and 20 use several sources together. Gloss before reading: a "retort" is a glass vessel with a long bent neck used for heating substances, a "taper" is a thin candle, and "elastic fluid" means gas.

   1In the next place, I took the 45 grains of red matter formed during this experiment, which I put into a small glass retort, having a proper apparatus for receiving such liquid, or gasseous product, as might be extracted: Having applied a fire to the retort in a furnace, I observed that, in proportion as the red matter became heated, the intensity of its colour augmented. When the retort was almost red hot, the red matter began gradually to decrease in bulk, and in a few minutes after it disappeared altogether; at the same time 41-1/2 grains of running mercury were collected in the recipient, and 7 or 8 cubical inches of elastic fluid, greatly more capable of supporting both respiration and combustion than atmospherical air, were collected in the bell-glass.

   2A part of this air being put into a glass tube of about an inch diameter, showed the following properties: A taper burned in it with a dazzling splendour, and charcoal, instead of consuming quietly as it does in common air, burnt with a flame, attended with a decrepitating noise, like phosphorus, and threw out such a brilliant light that the eyes could hardly endure it. This species of air was discovered almost at the same time by Mr Priestley, Mr Scheele, and myself. Mr Priestley gave it the name of dephlogisticated air, Mr Scheele called it empyreal air. At first I named it highly respirable air, to which has since been substituted the term of vital air. We shall presently see what we ought to think of these denominations.

   3In reflecting upon the circumstances of this experiment, we readily perceive, that the mercury, during its calcination, absorbs the salubrious and respirable part of the air, or, to speak more strictly, the base of this respirable part; that the remaining air is a species of mephitis, incapable of supporting combustion or respiration; and consequently that atmospheric air is composed of two elastic fluids of different and opposite qualities. As a proof of this important truth, if we recombine these two elastic fluids, which we have separately obtained in the above experiment, viz. the 42 cubical inches of mephitis, with the 8 cubical inches of respirable air, we reproduce an air precisely similar to that of the atmosphere, and possessing nearly the same power of supporting combustion and respiration, and of contributing to the calcination of metals.

   4Although this experiment furnishes us with a very simple means of obtaining the two principal elastic fluids which compose our atmosphere, separate from each other, yet it does not give us an exact idea of the proportion in which these two enter into its composition: For the attraction of mercury to the respirable part of the air, or rather to its base, is not sufficiently strong to overcome all the circumstances which oppose this union. These obstacles are the mutual adhesion of the two constituent parts of the atmosphere for each other, and the elective attraction which unites the base of vital air with caloric; in consequence of these, when the calcination ends, or is at least carried as far as is possible, in a determinate quantity of atmospheric air, there still remains a portion of respirable air united to the mephitis, which the mercury cannot separate. I shall afterwards show, that, at least in our climate, the atmospheric air is composed of respirable and mephitic airs, in the proportion of 27 and 73; and I shall then discuss the causes of the uncertainty which still exists with respect to the exactness of that proportion.

5. Closure5 minutes

   Exit ticket: "Write one sentence comparing your class result with one finding from a text, and one sentence saying which earlier explanation or account your result supports or contradicts, and how strongly." Sort the tickets into "comparison with a number and a judgment," "comparison without a judgment" and "judgment without a comparison" to plan the next lesson.

   Teacher note on the historical texts. Lavoisier and Ramsay write in the language of their time. "Animals being introduced into it were suffocated" in T1 describes animal experiments that were routine in eighteenth-century chemistry; discuss them as part of the history, and let students who find them upsetting focus on the measurements. Words such as "salubrious" (healthy), "mephitis" (unbreathable air) and "caloric" (heat, then thought to be a substance) are period vocabulary. The texts contain no slurs. Lavoisier's view that oxygen combines with metals and fuels when they burn is the modern view; his "caloric" and his figure of 27 percent were later abandoned. Mercury and its red calx are toxic: they appear on this page as data only.

   Homework passage. The homework uses a later part of Ramsay's book, below: Lord Rayleigh's measurements of the densities of air, oxygen and nitrogen, published in 1893, and a puzzle they raised.

   1Up to within the last few years it was supposed that the constituents of air had all been discovered. But Lord Rayleigh and Professor William Ramsay have recently found that the supposed nitrogen of the air is in reality a mixture of nitrogen with a new gaseous element, to which they have given the name “argon,” on account of its chemical inactivity (ἂργον, idle, inactive).

   2[...] He found the weights of one litre of oxygen, nitrogen, and air to be

   3Oxygen 1·42952 grams
   “Nitrogen” 1·25718 "
   Air 1·29327 "

   4A simple calculation leads to the composition of purified air. The percentage of oxygen must be 20·941, and that of “nitrogen” 79·059, in order to give a mixture of which the weight of a litre is 1·29327. Now, this corresponds with the results of the best analyses, quoted above. And the accuracy of these determinations of density is confirmed by this means, as well as by results of other experiments made by Leduc, von Jolly, and Morley.

   [...]

   5It was next deemed necessary to test whether nitrogen was homogeneous by preparing it too by several different methods. In the same paper Lord Rayleigh (p. 146) mentions that nitrogen, prepared from ammonia, its compound with hydrogen, is somewhat lighter than “atmospheric nitrogen,” the deficiency in weight amounting to about 1 part in 200. Now it is evident from inspection of the numbers quoted above, that the accuracy of the density determination may be trusted to within 1 part in 10,000, and that the balance would detect a discrepancy one-fiftieth of that observed in the densities of “atmospheric” and “chemical” nitrogen. In a letter to Nature, Lord Rayleigh asked for suggestions from chemists as to the reason of this curious anomaly, but his letter went without reply. [...]

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   In T4, paragraph 1, Lavoisier heats the 45 grains of red matter and collects 41 1/2 grains of mercury and 7 or 8 cubic inches of gas. The phlogiston theory held that a metal is its calx plus phlogiston, so a calx should weigh less than the metal it comes from. Which finding contradicts that account?

   AThe red matter grew brighter in color as it was heated BThe red matter weighed more than the mercury it gave back CThe mercury that came back was running, liquid mercury, not a powder DThe gas that came back could be caught in a bell-glass

2. Question 2 of 20 · Multiple Choice

   In T4, paragraph 2, Lavoisier lists the names Priestley and Scheele gave the new gas and adds, "We shall presently see what we ought to think of these denominations." What is the main point of the paragraph for a reader comparing sources?

   APriestley and Scheele found the gas first, so Lavoisier's findings add nothing new BThe three chemists found different gases, so their findings cannot be compared CThree chemists found the same gas, but the names they gave it rest on different explanations DLavoisier's name for the gas is the only one of the three that describes how it was made

3. Question 3 of 20 · Multiple Choice

   In T4, paragraph 3, what does Lavoisier offer as proof that atmospheric air is made of two different gases?

   AMixing the two gases he had separated gave back an air very like the atmosphere BThe mercury turned red on the second day and stopped changing after about a week CThe air left in the bell-glass was measured at a standard pressure and temperature DPriestley and Scheele had already reached the same conclusion about the air

4. Question 4 of 20 · Multiple Choice

   In T4, paragraph 4, Lavoisier states that atmospheric air is made of respirable and mephitic airs "in the proportion of 27 and 73." How does this compare with Cavendish's finding in T2?

   AThe two agree to within one percentage point on the respirable part BLavoisier's figure for the respirable part is about 52 points higher CLavoisier's figure for the respirable part is about 6 points lower DLavoisier's figure for the respirable part is about 6 points higher

5. Question 5 of 20 · Multiple Choice

   Lavoisier's own experiment in T1 used up only about 1/6 of the air, yet in T4 he gives 27 parts in 100 for the respirable part. How does T4, paragraph 4, explain why the experiment took up less?

   ASome of the respirable air leaked out of the bell-glass during the twelve days BThe mercury could not pull all the respirable part away from the other part of the air CThe furnace heated the air, so the volumes could not be measured at the end DThe bell-glass was too small to hold all of the respirable air in the sample

6. Question 6 of 20 · Multiple Choice

   Suppose Lavoisier's figure of 27 parts in 100 were correct. About how many cubic inches of respirable air should his 50 cubic inches of air in T1 have held?

   AAbout 36.5 cubic inches BAbout 8.3 cubic inches CAbout 23 cubic inches DAbout 13.5 cubic inches

7. Question 7 of 20 · Multiple Choice

   In the lab report (T3), which group's result should be set aside before the class compares its findings with Lavoisier's and Cavendish's, and why?

   AGroup 4, because its air column was the longest at the start BGroup 1, because it read its tube after 24 hours as well as after 3 days CGroup 5, because its steel wool was not soaked, so its rusting was slowed DGroup 6, because its result is closest to the modern value for oxygen

8. Question 8 of 20 · Multiple Choice

   Group 4's air column in T3 went from 155 mm to 124 mm. What percent of the air was used up?

   AAbout 25.0 percent BAbout 20.0 percent CAbout 80.0 percent DAbout 31.0 percent

9. Question 9 of 20 · Multiple Choice

   In T3, Groups 1-3 read their tubes after 24 hours as well. A student notices that their 24-hour results, about 15-16 percent, are close to Lavoisier's "about 1/6" and says, "So the 24-hour readings support Lavoisier's number." What is the best reply?

   AThe 24-hour readings were taken before the rusting had finished, so their closeness to 1/6 is a coincidence BThe 24-hour readings support Lavoisier's number, because 15-16 percent rounds to one sixth CThe 24-hour readings contradict Lavoisier, because his experiment ran for twelve days DThe 24-hour readings cannot be compared with anything, because they were taken on a different day

10. Question 10 of 20 · Multiple Choice

    Leaving out Group 5, what is the mean of the percentages of air used up by the other five groups in T3?

    AAbout 19.6 percent BAbout 17.8 percent CAbout 80.4 percent DAbout 21.0 percent

11. Question 11 of 20 · Multiple Choice

    In Diagram 2, which finding is farthest from the modern value for oxygen in dry air?

    ALavoisier's mercury result BCavendish's analyses of 1781 CLavoisier's stated proportion DAll three are equally far from it

12. Question 12 of 20 · Multiple Choice

    In T1, paragraph 2, Lavoisier says he "was obliged to repeat this experiment several times" and will "give in one detail the results of two or three experiments of the same nature." Why does this matter when you compare his numbers with another source?

    AIt shows that his numbers were copied from the experiments that Priestley and Scheele reported BIt shows that the 50 and 42-43 cubic inches were measured in a single, unbroken run CIt shows that his experiment failed and that his numbers should not be used at all DIt shows that his account combines results from several runs, so its numbers are approximate

13. Question 13 of 20 · Multiple Choice

    T1, paragraph 3, says the air left after the experiment "was no longer fit either for respiration or for combustion." Which observation from the class steel-wool test would support this finding?

    AThe water rose in the tube while the steel wool rusted BThe air left in a tube put out a burning splint CThe steel wool turned orange-brown during the three days DThe water level stopped rising between day 2 and day 3

14. Question 14 of 20 · Multiple Choice

    In T2, Ramsay says Cavendish's result "does not differ materially" from the best modern analyses. By how many percentage points do the two figures for oxygen differ?

    AAbout 0.12 points BAbout 1.2 points CAbout 58.3 points DAbout 0.21 points

15. Question 15 of 20 · Short Answer

    T4, paragraph 3, says atmospheric air "is composed of two elastic fluids of different and opposite qualities." Does the class steel-wool test (T3) support or contradict this finding? Explain, using one detail from T3 and one from T4.

    Show model answer

16. Question 16 of 20 · Short Answer

    Modern chemistry gives the red calx as mercury(II) oxide, HgO, which is 92.6 percent mercury by mass. Compare this with Lavoisier's weights in T4, paragraph 1. Does the modern figure support or contradict his finding?

    Show model answer

17. Question 17 of 20 · Short Answer

    At the end of Lavoisier's experiment, 42 of the original 50 cubic inches of air were left (T4, paragraph 3, and T1). If the air were 79.05 percent unbreathable gas, as the modern table implies, how much should have been left? What does the comparison suggest?

    Show model answer

18. Question 18 of 20 · Short Answer

    T3 ends: "So air is about 20 percent oxygen, and Lavoisier was wrong." Rewrite this conclusion so that it matches the evidence. Say which of Lavoisier's findings the class result contradicts and which it supports.

    Show model answer

19. Question 19 of 20 · Short Answer

    Name one difference between the methods of Cavendish (T2) and the class steel-wool test (T3) that should make Cavendish's figure more trustworthy, and one reason the class test is still worth comparing with it.

    Show model answer

20. Question 20 of 20 · Short Answer

    Using at least three sources on this page, write three or four sentences that compare and contrast their findings on how much of the air is oxygen, and name one earlier explanation or account that these findings contradict.

    Show model answer

These standards connect to RST.9-10.9: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: Common Core State Standards for English Language Arts & Literacy. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.