Exercises in Practical Chemistry (Volume 1)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1869 Excerpt: ...chloride to make the solution give an acid reaction to test-paper. Dip into the solution one-half of a slip of turmeric-paper, and dry it at a gentle heat, by holding it before the fire; the dipped portion will be coloured red. If a drop of sodium carbonate be placed on the reddened portion of the turmeric-paper, the colour will be changed to black. SILICATES. 1. The best method of obtaining silicon dioxide in a pure state has already been given, p. 114. 2. Heat a piece of flint to full redness in a common fire, and quench it suddenly in water. It will then form a white friable mass, about 1 grm. of which should be ground to powder in a mortar, mixed with four times its weight of sodium carbonate, and fused in a platinum crucible, or on a piece of platinum foil turned up at the edges. A full red-heat, such as that of a gas blowpipe, will be required for the fusion. Pour a little water over the fused mass when it is cold, and boil it rather quickly over a lamp. By this means the whole of the sodium silicate may generally be detached from the crucible, and should then be boiled for some time in a beaker. You will thus obtain a solution of sodium silicate, similar to that which is called 'soluble glass, ' with which the following experiments should be tried: --(a) Add a few drops of hydrogen chloride to a portion of the hot solution, in a test-tube. A dense gelatinous precipitate will be formed of hydrogen silicate, and, if the solution of sodium silicate is strong, the whole will appear to solidify. (b) Place some dilute hydrogen chloride in a test-tube, and add drop by drop a little of the solution of sodium silicate, which should be diluted, if strong. No permanent precipitate will now be formed, since the hydrogen silicate is retained in solution when thus f...