When substances readily combine with water to form hydrates, the heat of solution in water is usually positive; when, on the other hand, they do not readily form hydrates, or when they are already hydrated, the heat of solution is usually negative.
The alkalis are used almost exclusively in the condition of caustic lyessolutions of their respective hydrates in water.
Berzelius's investigation of the action of the electric current on salts clearly demonstrated the invaluable assistance that electrolysis could render to the isolator of elements; and the adoption of this method by Sir Humphry Davy for the analysis of the hydrates of the metals of the alkalis and alkaline earths, and the results which he thus achieved, established its potency.
If phosphoric acid is absent, aluminium, chromium and ferric hydrates are precipitated.
It forms crystallizable salts with potassium and calcium hydrates, and functions as a weak acid forming salts named plumbates.
Various hydrates have been described, but they cannot be formed by precipitating a uranyl salt with an alkali, this reagent giving rise to salts termed uranates.
(2) A similar oxide (flores jovis) is produced by burning tin in air at high temperatures or exposing any of the hydrates to a strong red heat.
The chloride unites energetically with water to form crystalline hydrates (e.g.
Tin and antimony (also arsenic) are converted by it (ultimately) into hydrates of their highest oxides Sn0 2, Sb205 (As 2 O 5) - the oxides of tin and antimony being insoluble in water and in the acid itself.
Dumas, who regarded them as hydrates of olefiant gas (ethylene); on the other they yielded chloroform, chloral and aldehyde, as well as other compounds of less general interest, and also the method of forming mirrors by depositing silver from a slightly ammoniacal solution by acet aldehyde.
In modern chemistry alkali is a general term used for compounds which have the property of neutralizing acids, and is applied more particularly to the highly soluble hydrates of sodium and potassium and of the three rarer "alkali metals," caesium, rubidium and lithium, also to aqueous ammonia.
In a smaller degree these alkaline properties are shared by the less soluble hydrates of the "metals of the alkaline earths," calcium, barium and strontium, and by thallium hydrate.
His analytical skill enabled him to demonstrate the inaccuracy of the researches by which Berthollet attempted to support the opposite view, and to show among other things that some of the compounds which Berthollet treated as oxides were in reality hydrates containing chemically combined water, and the upshot was that by 1808 he had fully vindicated his position.
Davy, inspired by his successful isolation of the metals sodium and potassium by the electrolysis of their hydrates, attempted to decompose a mixture of lime and mercuric oxide by the electric current; an amalgam of calcium was obtained, but the separation of the mercury was so difficult that even Davy himself was not sure as to whether he had obtained pure metallic calcium.
Several hydrates are known: 2NaOH 7H 2 O is obtained as large monoclinic crystals by' cooling a solution of specific gravity 1.365 to -8'; Pickering (Journ.
On solution in water, heat is evolved and hydrates formed.
Both these hydrates occur in the mineral kingdom, the former as natron and the latter as thermonatrite.
As we have seen, the maxima of the various curve-branches at C, E, G, and J correspond with the melting points of the various hydrates at 37°, 32.5°, 56° and 73.5° respectively; and at these points melting or solidification of the whole mass can occur at constant temperature.
On the hydrates of nitric acid see V.
Both these soluble hydrates are readily coagulated by traces of a salt, acid or alkali; Crum's hydrate does not combine with dye-stuffs, neither is it soluble in excess of acid, while Graham's compound readily forms lakes, and readily dissolves when coagulated in acids.
Under all these three conditions the diamond is associated with fragments of the rocks of the country and the minerals derived from them, 'especially quartz, hornstone, jasper, the polymorphous oxide of titanium (rutile, anatase and brookite), oxides and hydrates of iron (magnetite, ilmenite, haematite, limonite), oxide of tin, iron pyrites, tourmaline, garnet, xenotime, monazite, kyanite, diaspore, sphene, topaz, and several phosphates, and also gold.
Nickel sulphate, NiSO 4, is obtained anhydrous as a yellow powder when any of its hydrates are heated.
It forms hydrates containing one, two, five, six and seven molecules of water.
Hydrates, such as starches and sugars; fats; proteids, such as meat and eggs; salts; and last, but not least, water.
It combines with water, forming the hydrates SbC1 5 -1-1 2 0 and SbC1 3.4H 2 O; it also combines with phosphorus oxychloride, hydrocyanic acid, and cyanogen chloride.
Such substances are silver nitrate (lunar caustic), the caustic alkalis (potassium and sodium hydrates), zinc chloride, an acid solution of mercuric nitrate, and pure carbolic acid.
Both the monoand di-hydrates form frbeing mixtures with snow.
Other hydrates have also been described.
It forms several hydrates, the medicinal value of which was recognized in very remote times.
Two series of synthetic hydrates were recognized by Muck and Tommasi: the " red " hydrates, obtained by precipitating ferric salts with alkalis, and the " yellow " hydrates, obtained by oxidizing moist ferrous hydroxide or carbonates.
Van Bemmelen has shown that the red hydrates are really colloids, the amount of water retained being such that its vapour pressure equals the pressure of the aqueous vapour in the superincumbent atmosphere.
By heating freshly prepared red ferric hydrate with water under 5000 atmospheres pressure Ruff (Ber., 1901, 34, p. 34 1 7) obtained definite hydrates corresponding to the minerals limonite (30°-42, 5°), gothite (4 2.5°-62, 5°), and hydrohaematite (above 62.5°).
Other hydrates are known.