Watchglasses are round glass panes with a diameter of around 5 - 10cm, used in various experimental techniques. The border is bent upwards to allow the watchglass to hold small amounts of liquids in order to let them evaporate. The evaporation can be accelerated by heating the watchglass with a Bunsen burner. Watchglasses can also be used to cover Petri dishes or beakers, and are also suited to weighing small amounts of matter or drying them in an airing cupboard. The term watchglass is derived from the former pocket watches' protection glass which was often domed.
Erloju- beirak teknika esperimentaletan erabiltzen diran 5- 10 zm- ko diametroa duten beirazko panel biribilak dira. Ertza gorantz tolestuta dago lurrunketarako likido kantitate txikiak edukitzeko ahalmena izan dezaten. Lurrunketa erloju- beira Bunsen erregailu batekin berotuz bizkortzen da. Erloju- beirak ere Petri plakak edo prezipitazio- ontziak estaltzeko erabil daitezke. Gainaera materia kopuru txikiak pisatzeko edo lehortzeko egokiak dira. Erloju- beira izena aurretik zeregin hauetarako poltsikoko erlojuen beira erabiltzen zenetik dator.