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Most the necessary substances are fairly readily available in nature. White sand and salt can be found by or in the ocean. In addition, pyrolusite is a common ore of manganese and is readily available straight from the ground. For the sake of simplicity, we will study potash for the flux because potash is one of the simplest alkalis to obtain (in fact, it was the first one that man could produce). To produce potash, you must first burn wood to obtain its ashes. Wood ash is a complex heterogeneous mixture of everything left over after the wood and charcoal have burned away. In addition, many minerals in the tree will have been converted to carbonates because of the carbon dioxide in the fire gases, including the potassium carbonate we want:
Usually this mixture includes sodium and potassium carbonate, sodium and potassium chloride, silica, and calcium carbonate. For our glass, we wish to isolate the potassium carbonate. First, we place the ashes on straw and small sticks in an apparatus known as an ash hopper (fig. 4). Water is then poured over the ashes, through the straw and sticks and collected out the bottom of the hopper as lye. The water-soluble potassium and sodium salts dissolve into the water and are leached out
leaving the silica and calcium carbonate, which won't dissolve, behind. Next we will exploit that fact that carbonates are generally more soluble than chlorides and that potassium carbonate is even more soluble than sodium carbonate. First, we will bring the lye to a boil and boil off enough water so that a precipitate forms at the bottom. This solid precipitate is comprised of potassium and sodium chlorides. Once we see the precipitate forming, we will boil off half of the remaining water. Now we are fairly sure that no chlorides remain in solution. Then we will pour off the still-hot solution, leaving the solid behind. |
Next, we will allow the liquid to cool to room temperature, which causes the less-soluble sodium carbonate to come out of solution. Now we are left with a fairly pure potassium carbonate solution. This is then poured into a separate container, and the water is completely boiled off. Now we are finally left with almost pure K2CO3. Pyrolusite is a common ore of manganese and is readily available straight from the ground. They appear in nature as seen in fig. 5. Fig. 5
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