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Read about ordinary water and transform the word given in bold at the end of each line into a suitable form that fits the space in the same line.

Mercuric oxide is _1_ as a bright, orange-red, crystalline substance either by _2_ mercury in air or by the pyrolysis of mercuric nitrate. It is also obtained as a yellow precipitate when _3_, basic hydroxides are added to _4_ of mercuric nitrate, the hydroxide undergoing spontaneous _5_. The yellow oxide _6_ from the red only in that its particles are of _7_ size. Upon being heated it changes into the red _8_. The other mercuric salts are _9_ prepared by treating either the oxide or free mercury with the appropriate _10_.

obtain heat solution solutes composition difference small modify usual acidic

Metallic mercury can be obtained by heating the sulphide ore in air with sulphur dioxide as a by-product:

HgS+O₂ Hg+SO₂

Mercury vapour is condensed from the gaseous products. Mercury may be purified by washing it with dilute nitric acid, which oxidizes the more active metallic impurities present, especially zinc and cadmium.

Hot mercury vapour is known to conduct electricity and give out light that is rich in the ultraviolet rays.

The common metals except iron and platinum form alloys with mercury, known as amalgams.

18. Match the definitions in B with the notions in A:

A	B
1. Mercuric oxide	a. An alloy of mercury and a common metal
2. Metallic mercury	b. Crystalline substance obtained by the pyrolysis of mercuric nitrate.
3. Amalgam	c. By-product of the thermal reaction of sulphide ore with sulphur dioxide

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