) Na NaCl ) Na2SO4) Na2CO3) NaOH NaNO3) ) ) HNaCO3 From what is Na2SO4 prepared, as shown by the table? Na2CO3? Na? 227. Occurrence and Preparation of NaCl.--NaCl occurs in sea water, of which it constitutes about three per cent, in salt lakes, whose waters sometimes hold thirty per cent, or are nearly saturated, and, as rock salt, in large masses underground. Poland has a salt area of 10,000 square miles, in some parts of which the pure transparent rock salt is a quarter of a mile thick. In Spain there is a mountain of salt five hundred feet high and three miles in circumference. France obtains much salt from sea water. At high tide it flows into shallow basins, from which the sun evaporates the water, leaving NaCl to crystallize. In Norway it is separated by freezing water, and in Poland it is mined like coal. In New York and Michigan it is obtained by evaporating the brine of salt wells, either by air and the sun's heat, or by fire. Slow evaporation gives large crystals; rapid, small ones. 228. Uses.--The main uses are for domestic purposes and for making the Na and Cl compounds. In the United States the consumption amounts to more than forty pounds per year for every person. 229. Sodium Sulphate.--What acid and what base are represented by Na2SO4? Which is the stronger acid, HCl or H2SO4? Would the latter be apt to act on NaCl? Why? 230. Manufacture.--This comprises two stages shown by the following reactions, in which the first needs moderate heat only; the last, much greater. (1) 2 NaCl + H2SO4 = HNaSO4 + NaCl + HCl: (2) NaCl + HNaSO4 = Na2S4 + HCl. The operation is carried on in large furnaces. The gaseous HCl is passed into towers containing falling water in a fine spray, for which it has great affinity. The solution is drawn off at the base of the tower. Thus all commercial HCl is made as a by- product in manufacturing Na2SO4. When crystalline, sodium sulphate has ten molecules of water of crystallization (Na2SO4, 10 H2O); it is then known as Glauber's salt. This salt readily effloresces; i.e. loses its water of crystallization, and is reduced to a powder. Compute the percentage of water. 231. Uses.--The leading use of Na2SO4 is to make Na2CO3; it is also used to some extent in medicine, and in glass manufacture. 232. Sodium Carbonate.--Note the base and the acid which this salt represents. Test a solution of the salt with red and blue litmus, and notice the alkaline reaction. Do you see any reason for this reaction in the strong base and the weak acid represented by the salt?