CHEMISTRY. 



lime, forming chloride of lime, or bleaching- 

 powder ; when sulphuric acid is added to this 

 substance, sulphate of lime is formed, and chlorine 

 is set free. 



Chlorine has only a very slight affinity for oxy- 

 gen, so that the two elements do not directly 

 combine; and their compounds, when indirectly 

 produced, decompose very easily into chlorine and 

 oxygen, the decomposition usually taking place 

 with explosive violence. In these decompositions, 

 heat is given out. 



Of these we may mention Chloric Acid. An- 

 hydrous chloric acid (C1 2 O 6 ), corresponding to 

 anhydrous nitric acid (N 2 O 6 ), has not yet been 

 obtained, but many of its salts are well known. 

 Hydrated chloric acid (hydric chlorate, H 2 O,C1 2 O 6 

 or HClOs) is a very explosive and powerfully oxi- 

 dising liquid. Chlorate of potash (K2O,C1 2 O 6 or 

 KC1O 3 ) is important as a source of oxygen, and 

 as an ingredient in the composition with which 

 some kinds of lucifer-matches are tipped, and in 

 many fireworks. 



BROMINE and IODINE are elements closely re- 

 sembling chlorine in chemical character. They form 

 bromides and iodides with metals, hydrobromic 

 and hydriodic acids with hydrogen, and bromates 

 and iodates corresponding to the chlorates. Their 

 affinity for hydrogen and the metals is in the order 

 chlorine, bromine, iodine ; being greatest in the 

 case of chlorine, least in that of iodine. Their 

 affinity for oxygen is in exactly the opposite order ; 

 being greatest in the case of iodine, least in that 

 of chlorine 



Bromides occur in small quantity in sea-water 

 and many mineral springs, from the ' mother- 

 liquor ' of which (or liquid left after the removal of 

 the less soluble chloride of sodium) bromine is 

 obtained. Compounds of iodine occur in extremely 

 small quantity in sea-water, from which they are 

 removed by sea-weeds. Iodine is obtained from 

 the ' kelp' or ash of such sea-weeds. Bromine is a 

 volatile brown liquid ; iodine, a volatile black solid, 

 yielding a beautiful purple vapour when heated. 



SULPHUR occurs native in many volcanic dis- 

 tricts, most of the sulphur of commerce being 

 obtained from Sicily. It is purified by distillation, 

 and is met with in commerce either as ' flowers of 

 sulphur ' that is, a fine powder produced by rapidly 

 cooling the sulphur-vapour or as roll-sulphur, 

 cast in cylindrical moulds. When heated, sulphur 

 fuses, at a temperature of about 234 Fah- 

 renheit, forming a mobile liquid of a brownish 

 yellow colour. If this liquid is allowed to cool, 

 it solidifies into an ' allotropic ' modification of 

 sulphur. This form of sulphur differs from the 

 usual one : in colour, it is brownish yellow, instead 

 of bright yellow ; in specific gravity, it is somewhat 

 lighter than common sulphur ; and in crystalline 

 form. When kept, however, it changes back again 

 to the common form. If fused sulphur is heated, 

 it begins to become thick like treacle at a tem- 

 perature very little above 250 F. The thickness 

 increases as the temperature rises, until, at about 

 430 F. the vessel containing it can be inverted 

 without any of the sulphur pouring out ; about 

 ^40 F. it is again more liquid, and can be poured 

 out. If at this stage the sulphur is rapidly cooled 

 by pouring it into water, it is obtained in a 

 plastic form, elastic like india-rubber. This modi- 

 fication, when kept, passes back into the common 

 form of sulphur. 



Compounds of Sulphur and Oxygen. When 

 sulphur is burned in air or oxygen, it unites with 

 oxygen, and forms anhydrous sulphurous acid, a 

 colourless transparent gas, consisting of equal 

 weights of sulphur and oxygen. Its formula is 

 SO.;, its specific gravity is 2-25. It can easily be 

 condensed to a colourless liquid, and dissolves 

 readily in water ; one volume of water dissolving 

 about 30 volumes of the gas at ordinary tempera- 

 tures. The gas has the pungent smell of burning 

 sulphur, and cannot be breathed unless mixed 

 with a large quantity of air. It unites with bases, 

 forming sulphites, such as normal sulphite of 

 soda (Na 2 O,SO 2 or Na 2 SO 8 ), acid sulphite of soda 

 (Na 2 0,S0 2 ,H 2 0,S0 2 or NaHSO 3 ). Sulphurous 

 acid and the sulphites act as reducing agents 

 (p. 314), taking up oxygen to form sulphuric acid 

 or sulphates. Sulphurous acid acts also as a 

 bleaching agent, rendering certain animal and 

 vegetable colouring-matters colourless, and is used 

 for bleaching straw and woollen goods. 



Sulphurous acid is a weak acid, and the sulphites 

 are decomposed by most strong acids. 



Anhydrous sulphuric acid (SO 3 ) is a white crys- 

 talline solid, which unites with 'the production of 

 much heat with water to form hydrated sulphuric 

 acid (H 2 O,SO 3 or HgSO^. This is a colourless 

 liquid, of specific gravity about 18-4 as compared 

 with water. It is obtained by the oxidation of sul- 

 phurous acid. The operation is conducted in 

 large leaden chambers, into which are introduced 

 i. Sulphurous acid, formed by burning sulphur 

 or iron pyrites (a compound of sulphur and iron) ; 

 2. Steam ; 3. Nitric acid ; and 4. Atmospheric 

 air. The nitric acid oxidises the sulphurous acid 

 to sulphuric acid, which unites with water from 

 the steam the nitric acid being reduced to 

 nitric oxide (NO) (p. 321); this immediately takes 

 up oxygen from the air, and forms peroxide of 

 nitrogen (NO 2 ), which again oxidises more sul- 

 phurous acid, and is reduced to nitric oxide. By a 

 constant repetition of this process, a small quan- 

 tity of nitric acid suffices for the oxidation of a large 

 quantity of sulphurous acid. The sulphuric acid 

 thus formed is concentrated by heat, which drives 

 off much of the water, and leaves an acid nearly 

 corresponding to the formula H 2 O,SO 3 or H 2 SO 4 . 



Hydrated sulphuric acid has a great attraction 

 for water, and gives out much heat when mixed 

 with it It is a powerfully corrosive substance, 

 destroying animal and vegetable tissues, and is 

 sometimes used as a caustic in surgery. It is a 

 very strong acid, driving out most other acids 

 from their salts, and is used for preparing hydro- 

 chloric, nitric, acetic, and many other acids. 

 With bases it forms sulphates, such as normal 

 sulphate of potash (K 2 O,SO 3 or K 2 SO 4 ); acid sul- 

 phate of potash (K 2 O,SO 3 ,H 2 O,SO 3 or KHSO 4 ) ; 

 sulphate of lime (CaO,SO 3 or CaSOJ, &c. It is 

 often called oil of vitriol, because it can be obtained 

 by distilling green vitriol or ferrous sulphate 

 (FeO,SO 3 or FeSO 4 ). If the green vitriol be dry, 

 anhydrous sulphuric acid is obtained. A mixture 

 or solution of anhydrous sulphuric acid in hydrated 

 sulphuric acid is known as Nordhausen or fuming 

 sulphuric acid ; it is used for dissolving indigo. 



Sulphur unites with hydrogen, forming sul- 

 phuretted hydrogen (H 2 S); this is a colourless 

 transparent gas, of specific gravity 1-19. It can 

 be condensed by cold and pressure to a colourless 

 liquid. Water dissolves at ordinary temperatures 



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