Phlogiston - dephlogisticated air - Lavoisier

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Why do things burn?.

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Phlogiston - dephlogisticated air - Lavoisier

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1. Phlogiston - dephlogisticated air - Lavoisier

2. Why do things burn?

3. Georg Ernest Stahl (1660 – 1734) Principle is phlogiston (Greek – to set on fire)

4. Phlogiston Theory

5. Becher & Stahl Theory

6. Phlogiston

7. Phlogiston

8. Phlogiston

9. Phlogiston

10. Phlogiston

11. Problems with Phlogiston Theory

12. No Problems with weight

13. Phlogiston Theory

14. Phlogiston Theory

15. Phlogiston

16. Need to think gases

17. Need to think gases

18. Pneumatic Trough

19. Joseph Priestly (1733 – 1804)

20. Priestley’s new ‘air’ Discovered another form of air Mercury heated in air ?formed a red substance – “the precipitate per se” or calx (= mecuric oxide) When heated with no air - calx changed back into mercury and gave off a gas with most unusual properties Mice were particularly active in the new air

21. Priestley and “dephlogsticated air” Combustibles burned more brilliantly and rapidly in this gas A smoldering splint of wood thrust into a container of the gas burst into flame Priestley explained this phenomenon in terms of the phlogiston theory Splint of wood must given off phlogiston at a rapid pace The gas must have little or no phlogiston allowing it to accept the new phlogiston so easily Priestley therefore called his new gas "dephlogisticated air"

22. Priestley - “dephlogisticated air”

23. Cavendish burns “inflammable air” One theory ? phlogistication produces “fixed air” But, Cavendish showed: Inflammable air + common air = explosion and what remained didn’t cause precipitation of limewater [not “fixed air”] What was it?

24. Cavendish burns “inflammable air” Burned “inflammable air” + common air in closed container No loss of weight Inside of vessel became “dewy” 423 measures inflammable air phlogisticated 1000 measures of common air (optimal – 2 volumes inflammable to 1 volume dephlogisticated air) Note: Cavendish still interprets in terms of phlogiston theory Lavoisier rejects phlogiston theory interprets as evidence water not a simple substance but product of the combustion of two gases Hard blow at Greek theory of the elements

25. Cavendish and increase in weight of calx Dephlogisticated air = (“water” – F)

26. Lavoisier (1743 – 1794)

27. Attack on Myth of Transmutation - late 1770s Lowering of levels of oceans attributed to a transformation of water into earth Hypothesis accepted by chemists who boiled and found an earthy residue at the bottom of container Lavoisier boiled water for a hundred days in a "pelican“ Showed residue not due to transmutation of water, but to dissolving of pelican's inner surface Applied quantitative analysis Weighing before and after experiment

28. Lavoisier and Combustion

29. Lavoisier and Combustion

30. Lavoisier’s Explanations

31. Lavoisier’s Explanations

32. Lavoisier’s Burning Lens

33. Conservation of Mass Lavoisier states mass never created nor destroyed but shifted from one substance to another

34. Lavoisier and Oxygen Theory (Part I) Heated 4 ounces of mercury in a flask with 50 cubic inches of air 8 cubic inches of air used up (weighing 3 grains) remaining mercury and red powder on surface of mercury were 3 grains heavier new “air” in flask could not support life or burning

35. Lavoisier and Oxygen Theory (Part I) Removed all the red powder and heated it in another flask new gas produced – volume 8 cubic inches and weight of 3 grains Originally ? 8 cubic inches of air used up (weighing 3 grains) new gas supported life and burning substances burned in it produced acids therefore “oxygen” = acid producer (Greek)

36. Test of Phlogiston vs.Oxygen Theories

37. Test of Phlogiston vs.Oxygen Theories

38. Test of Phlogiston vs.Oxygen Theories

39. Test of Phlogiston vs.Oxygen Theories

40. Test of Phlogiston vs.Oxygen Theories

41. Test of Phlogiston Theory

42. Test of Phlogiston Theory

43. What is air? Cavendish ? 79.167 % phlogisticated air ? 20.833 % dephlogisticated air "...whether there are not in reality many different substances confounded together by us under the name of phlogisticated air" [Black’s “Fixed Air”]?? Lord Rayleigh (100 years later) established a third gas to be argon

44. What is air?

45. Oxygen and Life

46. The idea of an element Ancients ? elements fundamental types of matter Small number of elements ? unification yield more complete and powerful explanation Ancient Greeks ? four Earthly elements and aether in the celestial sphere Alchemists added the principles of sulfur and mercury to explain the nature of metals - Paracelsus later added salt These systems of elements or principles persisted into 1700’s

47. The idea of an element - Boyle In The Sceptical Chymist: ? gold behaves chemically as would expect an element to behave Gold can be chemical combined with other materials, then separated out again into its “pure” form Gold has consistent properties - same density, color, malleability, etc No attempt to identify other materials satisfying the criteria he gave ?did not develop a system of elements

48. The idea of an element Lavoisier did develop such a system of elements Many of Lavoisier’s elements well known in the time of Boyle and Newton Discovery of various airs instrumental for Lavoisier trying to make sense of these new observations idea of oxygen, hydrogen, and nitrogen as elements hypothesis water is not an element but composed of the elements hydrogen and oxygen

49. The idea of an element - Lavoisier Altered definition of an element and criteria to identify elements Boyle and Newton - retained ancient idea of elements as a small number of truly fundamental types of matter Lavoisier ? “all we dare venture to affirm of any substance is, that it must be considered as simple in the present state of our knowledge, and so far as chemical analysis has hitherto been able to show.” “Table of Simple Substances” - not eternal unchanging list of elements - best list given the current state of chemical knowledge - contained 33 elements - no pretense of high degree of unification

50. New Chemical Nomenclature

51. Lavoisier’s Textbook

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