Sparingly soluble

C2H4N2O3, NH2CONHCOOH. Unknown in the free state as it breaks down immediately to urea and COi- The NH4, Ba, Ca, K and Na salts are known and are prepared by treating ethyl allophanate with the appropriate hydroxide. The esters with alcohols and phenols are crystalline solids, sparingly soluble in water and alcohol. They are formed by passing cyanic acid into alcohols or a solution of an alcohol or phenol in benzene. The amide of allophanic acid is biuret. Alcohols are sometimes isolated and identified by means of their allophanates. 

C4H6N2O2. Sublimes 260"C sparingly soluble in water hydrolysed by alkalis or mineral acids to glycylglycine. It and substituted dike-topiperazines are formed by the condensation of amino-acids, and are obtained in small quantities on the hydrolysis of proteins. 

Greenish-yellow needles or prisms, m.p. 148-149 C, sparingly soluble in cold water. Gives crystalline condensation products with aldehydes. 

C7H6O5. Colourless crystals with one molecule of water, m.p. 253" C, sparingly soluble in water and alcohol. It occurs free in woody tissue, in gall-nuts and in tea, and is a constituent of the tannins, from which it can be obtained by fermentation or by acid hydrolysis. It gives a blue-black colour with Fe and is used in the manufacture 6f inks. On heating it gives pyrogallol. 

Lead II) chloride, PbCl2. Insoluble cold water, sparingly soluble hot. Matlockite is PbFCl. PbCL forms many complex chlorides and also basic chlorides. Cassel yellow (approx. PbCl2 7PbO) is prepared by fusion of the constituents and is used as a pigment. 

CH OfiSj, H2C(S03H)2- a colourless, crystalline solid which readily absorbs water vapour decomposes on distillation. The potassium salt is prepared by heating methylene chloride with an aqueous solution of potassium sulphite under pressure at 150-I60" C. The free acid is obtained by decomposing the sparingly soluble barium salt with sulphuric acid. The aryl esters are very stable, but the alkyl esters decompose on heating to give ethers. Resembles malonic acid in some of its reactions. 

Colourless crystals m.p. 50 C, b.p. 301 C. Basic and forms sparingly soluble salts with mineral acids. Prepared by the reduction of 1-nitronaphthalene with iron and a trace of hydrochloric acid or by the action of ammonia upon l-naphlhol at a high temperature and pressure. 

In the case of a sparingly soluble salt that dissociates into v positive ions M and negative ions A, the solubility S is given by... 

The hydroxides M (OH)2 are generally less soluble and are of lower base strength. The Group I hydroxides are almost unique in possessing good solubility—most metal hydroxides are insoluble or sparingly soluble hence sodium hydroxide and, to a lesser extent potassium hydroxide, are widely used as sources of the hydroxide ion OH" both in the laboratory and on a large scale. 

The reaction between CaiOH), + COj to produce sparingly soluble CaCOj is the common test for carbon dioxide. 

Phosphine is a colourless gas at room temperature, boiling point 183K. with an unpleasant odour it is extremely poisonous. Like ammonia, phosphine has an essentially tetrahedral structure with one position occupied by a lone pair of electrons. Phosphorus, however, is a larger atom than nitrogen and the lone pair of electrons on the phosphorus are much less concentrated in space. Thus phosphine has a very much smaller dipole moment than ammonia. Hence phosphine is not associated (like ammonia) in the liquid state (see data in Table 9.2) and it is only sparingly soluble in water. 

On the addition of sodium hydroxide, the sparingly soluble sodium salt of methyl-orange, NaOsSCeHgN .NCgHgNfCHj), will crystallise out. 

Physical properties. Above members all colourless. Acetone, CH3COCH3, b.p. 56 soluble in water, characteristic odour. Ethyl methyl ketone, b.p. 80°, and diethyl ketone, b.p. 102 , are moderately and sparingly soluble in water respectively. Acetophenone,C6H5COCH3, m.p. 20, sparingly soluble, and benzophenone, m.p.48 ,... 

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