On Heating

Historically an earth was a non-metallic substance, nearly insoluble in water and unchanged on heating. The alkaline earth oxides, e.g. CaO, have an alkaline reaction in addition to being clearly earths . 

Anthranol is isomeric with anthrone, and behaves in its reactions as a typical hydroxylic compound. The equilibrium mixture between the two compounds consists mainly of the keto form anthranol is largely converted into anthrone on heating. 

Antimony penioxide, Sb20j, is yellow (Sb plus cone. HNO3). Decomposes to Sb02 on heating. Gives antimonates(V) with alkalis. Used as a flame retardant. 

It is the simplest compound containing the -N = N- chromophore, but is of no practical importance since it lacks affinity for fibres. Normally it exists in the most stable trans form, but may be converted to a less stable, bright red as form, m.p. 71 -S C by ultra-violet irradiation. Cis to irans isomerization occurs rapidly on heating. 

Copper Il) sulphide, CuS. Black solid, Cu plus excess S or copper(II) salt plus H2S. Decomposes to copper(l) sulphide, CU2S, on heating. 

It has a limited use in the preparation of the phthalocyanine pigments into which it is readily converted on heating with metallic salts. 

Dewar benzene is a valence isomer of benzene, to which it reverts on heating. 

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. 

HOOCCH2CH2CH2COOH. M.p. 97-98 C, b.p. 302-304°C. Prepared by treating 1,3-dichloropropane with sodium cyanide and heating the product with NaOH. Forms an anhydride on heating at 230-280 C. glutathione, glutamylcysteinylglycine, GSH, CioH. NaOfiS. M.p. 190-192 C (decomp.). 

C, obtained from the wool oil of Bulnesia sarmienti, Lorenz. On heating with sulphur it gives guaiazulene. 

Ironiffl) sulphate, Fe2(S04)3, 12, 10, 9, 7, 6, 3 and 0 H2O. Formed from Fe(IIl) salts plus (NH4)2S04. Decomposes to FcjOj and SO3 on heating. Sulphate complexes and alums are also known. 

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