CARE & MAINTENANCE
 

HEATING & COOLING

Glass may suffer damage in three ways:
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    Thick walled glassware should not be subjected to direct flame or other localized heat source. Vessels of this type are best heated with the use of an electric immersion heater
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    Avoid heating glassware over electric heaters with open elements. Uneven heat of this type can induce localized stress and increase the chances of breakage
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    Remember that a hot plate will retain heat long after the appliance has been switched off
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    Always ensure that the surface of the hot plate is larger in area than the base of the vessel being heated. An under sized plate for the job in hand will invite uneven heating and promote breakage of glassware
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    Always ensure that manufacturer’s instructions are followed when using electrical heat sources
        MIXING & STIRRING
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    Always use a ‘policemen’ or similar device on stirring rods of the vessel
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    When using a glass vessel with a magnetic stirrer always use a covered follower to prevent abrading the inside of the vessel
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    When using glass or metal mechanical stirrer in a glass vessel always predetermine the height of the stirrer before use to ensure there is no contact between the stirrer blade and the bottom or sides of the vessel
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    Never mix sulphuric acid and water inside a glass measuring cylinder. The heat of reaction can break the base of the cylinder
        VACUUM & PRESSURE
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    Never use a glassware beyond the recommended safe limit
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    Always use a safety screen when working with glassware subjected to pressure or vacuum
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    Never subject glassware to sudden pressure changes. Always apply and release positive and negative pressures gradually
     
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It may break under thermal stress in the ‘steady state’,that is when there is established a constant thermal gradient through the glass.
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It may break under the transient stress of a ‘thermalshock’ that is sudden heating or cooling
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It may, if heated beyond certain temperature, acquire apermanent stress on cooling which could causesubsequent failure
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The following advice will assist in avoiding failures during heating and cooling procedures:
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Never leave vessel unattended when evaporation work in being carried out. The vessel may crack or explode as“dryness” condition is approached if the heat source isas the liquid level drops
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Always the caution when removing glassware from aheat source and avoid placing on a cold or damp surface
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Although the ware can withstand extreme temperatures, sudden temperature changes may cause the vessel to break
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Always cool vessels slowly to prevent thermal breakage
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Never apply heat to badly scratched or etched vessel,as the thermal strength will have been greatly reduced
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Never apply point source heating to a vessel, as this will greatly increase the chance of breakage
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Always diffuse the heat source by using a metal gauzeor air / water bath. Alternatively, ensure even heating of the vessel by slow movement of the vessel in relation to the heat source
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Adjust Bunsen burner to get a large soft flame. It will heat slowly but also more uniformly. Uniform heat is critical factor for some chemical reactions
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Ensures that the flame contacts the vessel below the liquid level. Heating above that level will invite breakage of the vessels
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Always use anti-bumping devices in the vessel, such as powdered pumice or glass wool when rapid heating of the vessel and contents is required
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Never use material with sharp edges such as broken porcelain asan anti- bumping device. This will causeinternalabrasionsand educe the mechanical and thermal strength of the vessel.