CHEMISTRY\ 157 ACIDS AND ALKALIES. Nearly fill the tank with water and add a few drops of blue litmus solution ; then dip a glass rod into a weak acid solution of any convenient kind and gently stir the litmus solution with it : it will turn red in the neighborhood of the rod. After washing the rod, dip it into an alkaline solution of ammonia or potash, and again stir the solution in the tank. Blue clouds will form in the red sky upon the screen until the whole is again a beautiful blue. In place of litmus solution use a solution made by boiling purple cabbage. Acid turns this red, and an alkali turns it green. Such changes may be effected a number of times in succession in the same solution. Nearly fill the tank with sulphate of soda, in which is put either litmus or cabbage solution to color it ; the latter is the best. After projecting it as a blue solu¬ tion dip the terminals of a battery of three or four cells into it. Decomposition will begin and the acid and alkaline reactions will be observed about the poles. REACTIONS AND PRECIPITATION. Fill the clean tank nearly full of pure water and add a drop or two of a solution of nitrate of silver and stir it well. Then dip the glass rod into very dilute hydro¬ chloric acid. Very dense clouds of chloride of silver will form and fall to the bottom of the tank. Add a few drops of strong ammonia water, and the cloudy solution will again become clear. A small piece of carbonate of lime or of soda placed in the tank containing a very dilute solution of hydro¬ chloric acid gives up its carbonic acid in apparently large quantities