Many salts of the acid are known and, with the exception of those of the alkali metals, they are difficultly soluble in water.
Thus benzene, (CH) gives thiophene, (CH) S, from which it is difficultly distinguished; pyridine, (CH) N, gives thiazole, (CH) N S, which is a very similar substance; naphthalene gives thionaphthen, C 11 S, with which it shows great analogies, especially in the derivatives.
For substances of a difficultly combustible nature he adopted the method in common use to-day, viz.
After having previously roasted the tube and copper oxide, and reduced the copper spiral a, the weighed calcium chloride tube and potash bulbs are put in position, the boat containing the substance is inserted (in the case of a difficultly combustible substance it is desirable to mix it with cupric oxide or lead chromate), the copper spiral (d) replaced, and the air and oxygen supply connected up. The apparatus is then tested for leaks.
Difficultly volatile liquids may be weighed directly into the boat; volatile liquids are weighed in thin hermetically sealed bulbs, the necks of which are broken just before they are placed in the combustion tube.
They are quite insoluble in water and in salt solutions, and difficultly soluble in dilute acids and alkalies.
Lead nitrate, Pb(N03)2, is obtained by dissolving the metal or oxide in aqueous nitric acid; it forms white crystals, difficultly soluble in cold water, readily in hot water and almost insoluble in strong nitric acid.
All sugars are colourless solids or syrups, which char on strong heating; they are soluble in water, forming sweet solutions but difficultly soluble in alcohol.
When slowly crystallized it forms large monoclinic prisms which are readily soluble in water but difficultly soluble in alcohol.
It is difficultly fermented by yeast, but readily by the lactic acid bacillus.
It is a crystalline powder difficultly soluble in water and melting at 210° C. (with decomposition).
It is one of the most difficultly liquefiable gases, its critical temperature being - 139'5° C., and its critical pressure 35'5 atmos.
Arecaidine forms white crystals easily soluble in water, and difficultly soluble in alcohol.
Boric acid crystallizes from water in white nacreous laminae belonging to the triclinic system; it is difficultly soluble in cold water, but dissolves readily in hot water.
Again, the diazonium chlorides combine with platinic chloride to form difficultly soluble double platinum salts, such as (C 6 H 5 N 2 C1) 2 PtC1 4; similar gold salts, C 6 H,N 2 C1 AuC1 3, are known.
Nickel fluoride, NiF 2, obtained by the action of hydrofluoric acid on nickel chloride, crystallizes in yellowish green prisms which volatilise above m000° C. It is difficultly soluble in water, and combines with the alkaline fluorides to form double salts.
Occasionally this residue contains a small amount of iron in a difficultly soluble form; in that case the solution is slightly diluted with water and filtered into a larger flask.
Its salts are known as bromates, and are as a general rule difficultly soluble in water, and decomposed by heat, with evolution of oxygen.
In its properties it shows some analogy to the halogen acids, since it forms difficultly soluble lead, silver and mercurous salts.