233. Manufacture.--Na2CO3 is not made by the union of an acid and a base, nor is H2CO3 strong enough to act on many salts. The process must be indirect. This consists in reducing Na2SO, to Na2S, by taking away the O with C, charcoal, and then changing Na2S to Na2O3 by CaCO3, limestone. The three substances, Na2SO4, C, CaCO3, are mixed together and strongly heated. The reactions should be carefully studied, as the process is one of much importance. (1) Na2SO4 + 4 C = Na2S + 4 CO. (2) Na2S + CaCO3 = CaS + Na2CO3. Observe that C is the reducing agent. The gas CO escapes. The solid products Na2CO3 and CaS form black ash, the former being very soluble, the latter only sparingly soluble in water. Na2CO3 is dissolved out by water, and the water is evaporated. This gives commercial soda. CaS, the waste compound in the process, contains the S originally in the H2SO4 used. This can be partially separated and again made into acid. Describe the manufacture of NaCO3 in full, starting with NaCl. This is called the Le Blanc process, but is not the only one now employed to produce this important article. 234. Occurrence.-Sodium carbonate is found native in small quantities. It forms the chief surface deposit of the "alkali belt" in western United States, where it often forms incrustations from an inch to a foot in thickness. It was formerly obtained from sea-weeds, by leaching their ashes, as, by a like process, K2CO3 was obtained from land plants. 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?