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654.

Watchglass

655.

Watchglasses are round glass panes with a diameter of around 5 - 10 cm which are used in the 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. Moreover watchglasses are suited to weighing small amounts of matter or alternatively drying them in the airing cupboard. The term watchglass is derived from the former pocket watches' protection glass which was often domed.

657.

A dehydrator is a laboratory apparatus which is often made of glass and serves to dry chemical matters, that is, to remove water or liquid from a sample.
[tab][tab][tab]In principle it is a glass bowl with cap which has a planar grinding so that the bowl is air tight closeable. The dehydrator's lower part is ordinarily filled with a drying agent e.g. calcium chloride, silica gel, phosphoric anhydride or sulphuric acid. The sample to be dried is placed on a diaphanous cartridge of plastic or ceramics above the drying agent.
[tab][tab][tab]The drying agent is hygroscopic, which means that it dehumidifies its environment by absorbing water vapor. The dry atmosphere then takes up water from the sample to be dried.

658.

Spatula

659.

The spatula is a laboratory tool to scrape off, grind and transport chemicals. The material they are made of (e.g. iron, titanium, platinum) and their design (e.g. flat spatula or spoon spatula) can be different.

660.

Water Jet Pump

661.

The water jet pump has two entry pipes and one exit and consists in principle of two pipes one inside the other. At the water entry a water jet shoots under full pressure out of a nozzle into a slightly larger pipe. Thereby the water jet carries away air or fluid from the second entry. <br> this is caused by the negative pressure in a drifting fluid. Thus it is an application of the hydrodynamic paradox. This says that objects close to drifting fluids are aspirated instead of being pushed away.

662.

Refractometer

663.

With a refractometer the refractive index of optical media is determined. If the refractive index of a chemical is known it can be used after a synthesis to determine the sample's purity or to audit the synthesis' success.

664.

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