1. CONDUCTIVITY 2. A TIME REACTION F. E. BROWN Iowa State College, Ames, Iowa
CONDUCTIVITY MEASUREMENTS
This home-made apparatus' is mounted on a board 20 x 60 X 1.5 cm. It consists, first, of two binding posts for 110-volt alternat,ing current. From these I For a sketch of the apparatus see THIBJOURNAL, 14,384 (1937).
posts ihe current is led in two parallel circuit,^. The first circuit goes through a n incandescent lamp and a variable resistance which can be made large enough to dim or extinguish the lamp. The second circuit is led through a second similar incandescent lamp in series with a double-pronged set of dipping electrodes
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so fixed that the sum of the conductivities of two solu- A TIME REACTION; BETTENDORFF'S TEST FOR tions may be indicated by the brightness of the lamp. ARSENIC Then after mixing, the conductivity of the mixed soluSnCla reacts vith AsC18, or any simple arsenic comtions can he indicated similarly. pound in more or less concentrated HCI, to form SnCl, The procedure is: (1) measure a sum of conductivi- and a brown colloidal suspension. This reaction is ties snch that the lamp in tpe second circuit does not catalyzed by finely divided mercury produced by the dazzle the eyes; (2) set the variable resistance in the reduction of either HgClz or Hg2C12. The rate of the first circuit so that the lamps are equally bright; reaction is a function of temperature and concentration (3) partially or completely mix t,he solutions, insert of arsenic, mercury, and acid, and the appearance of the electrodes and compare the lamps; (4) try t o ex- the colloid may be immediate or may be delayed for plain the increase, decrease or constancy of the con- hours. Consequently, this reaction is ideal for setting ductivity after mixing. up a series of samples which require varying times to Seven experiments are suggested below: reach the same stage in the production of color. drop HCI (conc.) in 25 ml. of H 2 0and (1) Take Three series are suggested helon-: 125 ml. of distilled H20. Add the H,O in several porA. One drop of a saturated solution of NazHAsOa tions. in HC1 added to decreasing concentrations of HC1 (2) Take 3 drops NaOH (dil.) in 25 ml. of HzO and without a catalyst. 125 ml. of distilled HzO. Add H 4 0in several portions. 1 2 5 4 (3) Take 2 ml. of acetic acid (glacial) in 25 ml. of H 2 0and 125 ml. distilled H20. Add the H 2 0in several MI. of HC1.. . . . . . . . . . . . . . . . . . 24 21 18 14 portions. M1. of H,O.. . . . . . . . . . . . . . . . . . 0 3 6 10 (4) Take 5 ml. NHnOH (conc.) in 25 ml. of HzOand B. One drop of a saturat.ed solution of NazHAsOa add 125 ml. of H,O. Add the HzO in several portions. in HCI added to decreasing concentration of HC1 vith (5) Take 50 ml. of the dilute HC1 from (1) and 50 1 drop of 0.04 N solution of HgCh added. ml. of the diluted NaOH from (2) for sum of conductivities. Mix t,he two and find resultant conductivity. 1 2 5 4 (6) Take 50 ml. of the diluted acetic acid from (3) MI. of HCI.. . . . . . . . . . . . . . . . . 14 11 8 5 and 50 ml. of the diluted NHIOH from (4) for the sum MI. of HzO... . . . . . . . . . . . . . . . 10 13 16 19 of conductivities. Mix and find the resultant conC. One drop of a saturated solution of Na3HAs08 ductivity. in HC1 added to a mixture of 14 ml. of concentrated (7) Take 10 ml. of NH,OH in 50 ml. of HzO and HC1 and 10 ml. of H,O with varying amounts of a suspend AgCl in HzOfor sum of conductivities. Pour 0.004 N solution of HgClz added as follows: off water from AgCl so there will be no dilution of 1 2 5 4 5 NH40H. Then pour the NH40Hsolution on the AgCl and note the conductivity. Drops of 0.004 N HgC1,... 0 3 6 9 12
