After settling it is evaporated in iron pans.
The chlorides MgC1 21 A1C13, CrC1 3, FeC1 3, suffer a similar decomposition when evaporated with water in the heat.
Sodium aurosulphide, NaAuS 4H 2 O, is prepared by fusing gold with sodium sulphide and sulphur, the melt being extracted with water, filtered in an atmosphere of nitrogen, and evaporated in a vacuum over sulphuric acid.
The clear juice thus obtained is evaporated in a multiple-effect evaporator and crystallized in a vacuum pan, and the sugar is purged in centrifugals.
The solution obtained may be evaporated in vacuo until it attains a density of 1.46 when, if partially saturated with potassium hydroxide and filtered, it yields crystals of potassium pentathionate, K 2 S 5 0 6.3H 2 0.
And filtered, and neutralized with powdered chalk and a little milk of lime; the precipitate of calcium citrate so obtained is decomposed with dilute sulphuric acid, the solution filtered, evaporated to remove calcium sulphate and concentrated, preferably in vacuum pans.
A later method consists in boiling the weed with sodium carbonate; the liquid is filtered and hydrochloric acid added to the filtrate, when alginic acid is precipitated; this is also filtered off, the filtrate neutralized by caustic soda, and the whole evaporated to dryness and carbonized, the residue obtained being known as kelp substitute.
A hydrated chloride of composition 2CeC1 3.15H 2 O is also known, and is obtained when a solution of cerous oxide in hydrochloric acid is evaporated over sulphuric acid.
The liquid is then evaporated under a vacuum of 27 to 28 in.
Large quantities are also evaporated and exported.