A laboratory manual of electrotherapeutics . -imental battery and wash them clean, then fill each halffull with a neutral Na„S04 solution containing a little alco-holic solution of phenol-phthalein, and arrange them in arow. Connect the remaining four cells of your battery inseries and connect the wires of this battery to the endglasses containing the phenol-phthalein so that the wires 46 LABORATORY MANUAL dip into the fluid at the sides of the glasses. Completethe circuit through the remaining glasses by short piecesof copper wire, allowing the fluid in each glass to form aswide an interval i
A laboratory manual of electrotherapeutics . -imental battery and wash them clean, then fill each halffull with a neutral Na„S04 solution containing a little alco-holic solution of phenol-phthalein, and arrange them in arow. Connect the remaining four cells of your battery inseries and connect the wires of this battery to the endglasses containing the phenol-phthalein so that the wires 46 LABORATORY MANUAL dip into the fluid at the sides of the glasses. Completethe circuit through the remaining glasses by short piecesof copper wire, allowing the fluid in each glass to form aswide an interval in the circuit as possible. Measure thestrength of current passing and also note the change ofcolor in the cells throughout the row after the current haspassed for a few minutes. Phenol-phthalein is a delicatetest for the presence of an alkali. Why should this elec-trolytic change take place in the middle glasses with whichthe terminal wires are not in contact? Is the amount ofchemical action the same in each of the four electrolyticcells?. Fig. *8. Universal Connectors. Laws of Resistance.—In the solution of the prob-lems here given, the following brief summary of the lawsof resistance should be borne in mind: i. The resistance of conductors of the same mate-rial and thickness varies directly as the length. 2. The resistance of conductors of a given materialand length varies inversely as the area of cross of circles are proportional to the square of theirdiameters. 3. The resistance of a wire of a given length anddiameter depends upon the material of which it is made—that is, upon the specific resistance of the material. PROBLEMS. The following problems are given with the view ofputting into practice the facts and principles that havebeen treated of in the preceding experiments. To theseothers will be added when needed for the purpose of illus-trating or emphasizing certain rules or facts that may notseem to be fully grasped by the student. Problem i.—A ce
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