MERCURY SWITCHES for CONDUCTIVITY EXPERIMENTS EUGENE W. BLANK 241 N. Ninth St., Allentown. Pennsylvania
Thk paper describes the construction of mercury witches of the two-way, three-way, and reversing tyfies.
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N CONDUCTIVITY and electromotive force experiments frequent recourse is had to the so-called "commutators" which are simplyimprovised switches constructed of wax or wooden blocks with open pools of mercury to serve
switch may stand on edge A or B. The block should be of sufficient thickness to prevent the weight of the switch and connecting wires from overturning it. Figure 3 shows the construction of a three-way switch.
amalgamated ing as contact is done points.' wires by inserting into Switchthe
appropriate mercury contacts. Such switches have , several disadvantages, I : among which may be men. , tioned fouling and spilling I..----. .... of the mercury. B An improved switch may be readily constructed by n=Tincm. into sealing platinum electrodes I " appropriately shaped glass tubes. In this manner FIGURE1.-TWO-WAY the switch is effectually inSWITCH Current is distributed over sulated and there 's n' either of two paths depend- danger of 1merally loss. ing upon whether the switch ~i~~~ 1 sh,ows a simple rests on edge A or B. two-way swit;ch, while Figure 2 shows a reversing switch. Figure 3 illustrates a three-way switch. ' The two-way switchis constructed of a section of pyrex glass tubing 0.75 cm. in internal diameter and from 6 to 8 cm. in length. The platinum electrodes are soldered to flexible connections and the switch is mounted on a square of Transite. The Transite is mounted on a wooden block so that it may stand on either of the edges A or B. L The reversing switch is constructed in the same ~eneralmanner b 1 2 . 5 1 s0.. and mounted on a Transite rec2,-RBtangle which in turn is mounted smm upon a wooden block so that the ,,men + - --. .- Ye-1.
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FIGW 3.-TF~EB-WAY Swnm Current is distributed in any of three paths by turning switch so as to stand on edges A . B, or C.
The lives of these switches may be materially lengthened by filling with an inert gas (e. g., Nz) before sealing. To accomplish this a side arm must be sealed on the tube. Dry Nl is passed through for some minutes before sealing the electrode farthest from the point of entry of the Nz. The switch is completed by sealing off the side arm. The mercury used for filling these switches should be pure and cleame
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LAY. "Practical physical chemistry." 4th ed., Longmans, Green & co.. New York City, 1923, pp. 152, 196.
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switch so as to stand either on end A or B.
Human happiness depends chiefly upon having some o b M to pursue, and upon the &W' with which mr faculties are exerted in the pursuit.-Joseph Priestley
