Chemistry in the Modern Era
Terry Acree

• 1774: Conservation of Mass - Joseph Priestly, Antoine Laurent Lavoisier
  If you collect all the vapor and gases that evolve during a wine fermentation and weigh them, the weight would equal exactly the loss in weight of the grape juice as it became wine. A flash bulb weighs the same before at it used as it does after it is flashed. Chemical change in a closed system will not change the mass of the system.
• 1799: Definite Composition - Joseph Proust - isolated sugar (glucose) from grapes.
  If you examine the composition of 100 g of sugar isolated from grapes you always find 40 g of carbon (C) and 60 g of water. Further 60 g of water always contains 6.7 g of hydrogen (H) and 53.3 g of oxygen (O). The table below shows the definate composition of 100 grams (g) of grape sugar, grape acid, ethanol and carbon dioxide.

  	C	H	O
  sugar -	40.0g	6.7g	53.3g
  tartaric acid -	41.3g	3.4g	55.2g
  ethanol -	52.1g	13.0g	9.2g
  carbon dioxide -	27.3g	0g	72.7g

  Pure chemicals, sugar, salt, water, etc. are composed of elements, C, H, O, etc., in a definite formulation!!

• 1803: Multiple Proportions - Dalton - Small whole numbers!!!
  Atoms have a minumum unit weight called atomic weight and combine in "small whole numbers" to define molecules. For example, grape sugar has the empirical formular,
  C₆H₁₂O₆ ,

  where the unit weights (called atomic weights) are C = 12, H = 1, and O = 16.