Platinum, sealing into glass

There are no special requirements to be met for the counter electrode. Platinum wires or platinum wires sealed into glass with approximately 1 cm of exposed wire as shown in Fig. 

But perhaps the most satisfactory chemical process for the preparation of ozone is the electrolysis of dilute sulphuric acid. A 15 per cent, solution of acid is recommended, coupled with a high current density, namely, 80 amperes per sq. cm., at the (platinum) anode. Wflth a platinum-foil anode sealed into glass so that only athm edge is obtained projecting to an extent of about one-tenth of a millimetre, it is possible to produce oxygen containing over 20 per cent, of ozone by volume.5... 

The only difficult thing about this operation is obtaining the platinum. The tube or glass bulb is first drawn out to a jet and the wire is then inserted. The point of the jet is revolved in the flame until the glass melts. It is then allowed to cool very slowly, It is, of course, understood that wire made cf other metals cannot be sealed into glass owing to the unequal co-efficient of expansion of the two materials. 

Another interesting alloy, known as invar (p. 297) contains some 35 per cent of nickel and is particularly valuable for certain purposes such as clock pendulums, because of its negligible expansion with rise of temperature. An alloy containing 40 per cent of nickel expands by a similar amount as glass and may therefore be sealed into glass instead of the more expensive platinum which at one time had to be used for this reason the alloy is known as platinite (p. 297). 

The electrodes are circular platinum plates sealed into glass tubes, and electrical connection is made by means of mercury. These two tubes pass through an ebonite cover, and their relative positions must be fixed either by means of a glass tie, or by cementing the tubes to the cover. The cover is also furnished with two holes for the insertion of a thermometer (if desired) and of a pipette (see below). When not in use, these should be closed by means of small corks or rubber plugs. 

The introduction of the sample into the adsorbent layer is a critical process in HPTLC. For most quantitative work a platinum-iridium capillary of fixed volume (100 or 200 nL), sealed into a glass support capillary of larger bore, provides a convenient spotting device. The capillary tip is polished to provide a smooth, planar surface of small area (ca 0.05 mm2), which when used with a mechanical applicator minimises damage to the surface of the plate spotting by manual procedures invariably damages the surface. 

A length of 6-7 mm of platinum wire of 0.5 mm diameter sealed into a glass tube is satisfactory electrical connection is made by means of a copper wire dipping into a little mercury in contact with the platinum wire. 

Convenient dimensions for the anode are 3.75 by 6.0 cm. (the area of the anode [both sides] used by the checkers was 52 sq. cm.). Care should be taken to submerge it in the solution to a depth such that the oil which gathers on the top of the solution during the electrolysis will not insulate it, thus increasing the current density. The wire tab of the platinum sheet may be sealed into a glass tube so that only the sheet is exposed to the solution. 

The sodium hydroxide solution from a large bottle, and at room temperature, is caused to flow at the rate of 1 1. per hour through a pyrex glass tube equipped with an overflow for the solution and another tube for the gas outlet, and an inlet tube of copper or platinum for the fluorine as shown in Fig. 18. The inlet tube, which is sealed into the glass with red sealing wax, dips from 0.5 to 2 cm. into the alkali solution. The fluorine is passed directly from the generator into the inlet tube at the rate of from 1 to 3 1. per hour. If the fluorine is first condensed with liquid air, the yield is said to be very small.2 To the exit tube are attached first a gas wash bottle filled with water, (see Fig. 19) then a trap cooled with a solid carbon dioxide-alcohol mixture, and finally another trap cooled with liquid air. The OF2 is freed from any fluorine in the wash bottle, and the water vapor is frozen out in the first trap. The OF2—02 mixture condenses to a pale-yellow liquid in the... 

Solid electrodes in unstirred solution. The most useful solid electrodes are platinum, gold, vitreous carbon, and carbon paste. The preferred configuration for theoretical work is a flat planar surface sealed in glass with epoxy or snugly fitted into a Teflon shroud. The electrodes ordinarily are unshielded, although shielded designs have been described.94... 

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