235. Uses.—Na2CO3 forms the basis of many alkalies, as H2SO4 does of acids. Of all chemical compounds it is one of the most important, and its manufacture constitutes one of the greatest chemical industries. Its economical manufacture largely depends on the demand for HCl, which is always formed as a by-product. As but little HCl is used in this country, Na2CO3 is mostly manufactured in Europe. The chief uses are for glass and alkalies.
236. Sodium.—Na must always be kept under naphtha, or some other liquid compound containing no O, since it oxidizes at once on exposure to the air. For this reason it never occurs in a free state.
237. Preparation.-By depriving Na2CO3 of C and O, metallic sodium is formed. As usual, heated charcoal is the reducing agent. The end of the retort, which holds the mixture, dips under naphtha.
Na2CO3 + 2 C = 2 Na + 3 CO. The process is a difficult one, and Na brings five dollars per pound, though in its compounds it is a third as common as Fe. K is as abundant as Na, but more difficult of separation, and is worth three dollars per ounce. Notice the position of K and Na at the positive end of the elements.
238. Uses.—Na is used to reduce Al, Ca, Mg, Si, which are the most difficult elements to separate from their compounds. It acts in these cases as a reducing agent.
239. Sodium Hydrate. Review Experiment 62.
Experiment 118.—Put into a t.t. 10cc. H2O and 2 or 3 g. NaOH. Note its easy solubility. Test with litmus. Will it neutralize any acids?
240. Preparation. — Sodium hydrate, caustic soda, or soda by lime, is made by treating a solution of Na2CO3 with milk of lime. CaCO3 is precipitated and al- lowed to settle, the solution is poured off, and NaOH is obtained by evaporating the water and running the residue into molds.
241. Use.—NaOH is a powerful caustic, but its chief use is in making hard soap.
242. Hydrogen Sodium Carbonate.—Hydrogen so- dium carbonate, bicarbonate of sodium, acid sodium carbonate, cooking-soda, etc., HNaCO3, is prepared by passing CO2 into a solution of Na2CO3. Na2CO3 + H2O + CO2 = 2 HNaCO3. Test a solution of it with litmus. Account for the result. Its use in bread-making depends on the ease with which CO2 is liberated. Even a weak acid, as the lactic acid of sour milk, sets this free, and thus causes the dough to rise.