=258. Dilute sulphuric acid=, for these experiments, should be made by mixing 1 part, by volume, of concentrated acid, with 20 parts of water. Do not let the acid get upon clothes or carpets. Do not add water to acid. Mix by _slowly_ adding the acid to the water in a glass or earthen dish, stirring at the same time. Mix over a sink or out of doors. (For fuller details see App. Book; § 21, 22, 23, 24, 25.) To save time, make at least a quart of the mixture, bottle, and label it for use. =259. Directions.= (A) Bend over one end of each of the wires and metal strips, and hang them upon the edge of the tumbler (Fig. 81), so that their lower ends shall be in the acid. Do not let them touch each other. Stand the carbon rod in the acid. If there is no visible action upon any of the above substances, add a few drops of concentrated acid to the tumbler. Note carefully what takes place in the tumbler, and state which of the substances are dissolved, which simply made brighter, and which not acted upon at all. _=260. Discussion.=_ The bubbles of gas that arise from the zinc when it dissolves are hydrogen, and they indicate that a vigorous chemical action is going on in the tumbler, and that the zinc is being eaten away. [Illustration: Fig. 81.] [Illustration: Fig. 82.] =EXPERIMENT 109. To study the effect of dilute sulphuric acid upon various combinations of metals.= _Apparatus._ The same as in the last experiment. A small piece of amalgamated zinc, however, will be better than the whole strip. =261. Directions.= (A) Twist one end of the clean copper wire around the small piece of amalgamated zinc (Fig. 82). Hold one end of the wire in the hand and dip the combination into the acid. What takes place? Watch the surface of the copper, remembering that each, alone, was not acted upon by the acid (Exp. 108). (B) Use the clean iron wire in place of the copper wire, and repeat (A). Watch the surface of the iron. (C) With a string or thread tie a small piece of well amalgamated zinc to the carbon rod (Fig. 82), then dip the combination into the acid. Watch the surface of the carbon. _=262. Discussion.=_ While amalgamated zinc is not rapidly dissolved by dilute sulphuric acid, a vigorous action of some kind takes place when it is in contact with another metal or with carbon in the acid. The bubbles of hydrogen that are liberated do not seem to come from the zinc; they appear to grow, in the fluid, directly at the surface of the copper, iron, or other metal used with the zinc. This shows that something besides the mere dissolving of a metal takes place. Can we arrange our apparatus so that we can get some useful results from this action? =EXPERIMENT 110. To study the construction of a simple Voltaic or Galvanic cell.=