Mettler Toledo Excellence XP Bedienungsanleitung Seite 14

Density determination kit for Excellence XP/XS precision balances
14
Air bubbles
With poorly wetting liquids (e.g. water without wetting agent), it is possible that air bubbles remain adhered
to the immersed parts (solid, sinker, holder) and influence the result owing to their buoyancy. A bubble with
a diameter of 1 mm causes a buoyancy of 0.5 mg, whereas one of diameter 2 mm results in a buoyancy
as high as 4 mg. To avoid air bubbles, we advise the following precautionary measures:
– Degrease solvent-resistant solids
– Clean holders and sinker at regular intervals, never touched parts which are immersed with your hand
– Gently shake holders and sinker on first-time immersion to dislodge any air bubbles
– Remove tenaciously adhering air bubbles with a fine brush
– Use enclosed or commercial wetting agent or organic liquids (the density change experienced by distilled
water on the addition of wetting agent can be neglected).
Porosity of the solid
When solid bodies are immersed in a liquid, usually not all the air in the pores is displaced. This leads to
buoyancy errors and thus the density of porous bodies can only be determined approximately.