Soft Glasses

If preferred, suitable ignition tubes may be prepared by the student from soft glass tubing it is important that the thickness of the glass at the closed end be tmiform, otherwise the tube is likely to crack when heated. The simplest procedure is to blow a small bulb of uniform wall thickness at the end of the tube. The small test-tubes are available from all laboratory supply dealers... 

For apparatus made of soft glass, the volume contained or delivered at 20°C is given by... 

Temperature, °C Soft glass Heat-resistant glass... 

Carbon and Hydrogen.—Carbon compounds are frequently inflammable, and when heated on platinum foil take fipe or char and burn away. A safer test is to heat the substance with some easily reducible metallic oxide, the oxygen of which forms carbon diovide with the carbon present. Take a piece of soft glass tube about 13 cm. (5 in.) long, and fuse it together at one end. Heat a gram or two of fine copper oxide in a porcelain crucible for a few minutes to drive off the moisture, and let it cool in a desiccator. Mix it with about one-tenth of its bulk of powdered sugar in a mortar. Pour the mixture into the tube, the open end of which is now drawn out into a wide capillary and oeni. at the same time into the form Fig. i. 

The prepared flattened section is inserted into a glass sleeve shaped to fit, and the glass is fused on to the metal, pinched with tweezers and strongly heated. The seal must be carefully annealed. With soft glasses the copper glass interface is coloured red, while with harder glasses the colour is more of a yellowish red. 

Copper to soft glass seals are most easily made since the difference in expansion rates is least here, but satisfactory seals of copper to Pyrex can be formed with a little more care. A further factor with... 

Other workers who have reported STM under solution include Itaya et. al. (59) and Fan et. al. (Fan, F-R.F. Bard, A.J. Anal. Chem.. submitted). Their instruments each employ three orthogonal piezoelectric elements as tip translators and both use glass tip insulation, though their tip preparation techniques differ. In the former case, a 10 pm Pt wire was sealed into a capillary and subsequently etched, while the latter workers used a 65 pm Pt wire which was sealed in soft glass, turned on a lathe, and then sonicated in concentrated... 

Environmental water samples to be analyzed for metals are best stored in quartz or Teflon containers. However, because these containers are expensive, polypropylene containers are often used. Borosilicate glass may also be used, but soft glass should be avoided because it can leach traces of metals into the water. If silver is to be determined, the containers should be light absorbing (dark colored). Samples should be preserved by adding concentrated nitric acid so that the pH of the water is less than two. The iron in well water samples, for example, will precipitate as iron oxide upon exposure to air and would be lost to the analysis if not for this acidification. 

It is found that in alkaline solutions (Ph > H for soft glass) the glass no longer functions as a hydrogen electrode but is affected by an alteration in the sodium ion concentration of the solution. With sodium amalgams, in fact, glass may serve as a sodium electrode of constant thermodynamic potential. 

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