ACTIONS OF DOUBLE COMBINATION. 209 



hydrated, or combined with water, the product is a powerful acid ; 

 whereas slaked lime is an almost equally powerful antacid (Expt. 138). 

 Expt. 241. Combination of Liquids to form Liquids and 

 Solids. Chemical actions where two substances both in the liquid 

 state directly combine together (without the intervention of a 

 solvent to produce liquefaction) are comparatively rare, but are not 

 unknown. If melted sulphur be poured into a crucible containing 

 melted lead or zinc the two liquid substances combine together 

 and form metallic sulphides ; much as iron and copper combine with 

 sulphur (Expts. 205, 206). If a little mercury be poured into a 

 cup and a few drops of bromine added thereto and the whole 

 stirred together a vigorous action will take place, and the two 

 liquids will unite together forming ' solid bromide of mercury. 

 This experiment is one which should only be performed inside a 

 glassed-in draught place (Expt. 1 45), not only on account of the 

 danger of inhaling vapour of bromine (Compare Expts. 167 and 

 162) but also because fumes of mercury and bromide of mercury are 

 apt to be evolved, which also are highly deleterious when breathed. 



Actions of Double Combination. 



Expt. 242. Combustion of Sulphuretted Hydrogen. If sul- 

 phuretted hydrogen be generated instead of hydrogen in the appa- 

 ratus represented by fig. 56, using fragments of sulphide of iron 

 instead of granulated zinc, it can be burnt at a jet just as well as 

 hydrogen, the same precautions being requisite as to complete expul- 

 sion of air from the generator before applying a light in order to 

 avoid the chance of explosion (Expt. 207). Hold over the flame a 

 cold glass tumbler and you will see that water is deposited, just as 

 with hydrogen ; but besides this, the gas sulphur dioxide is formed, 

 as can be readily shown by its odour, and by collecting some of the hot 

 products of combustion in an inverted jar held over the flame, shak- 

 ing them up with water, and adding the solution to water rendered 

 blue with starch paste and a drop of weak iodine solution (Expt. 164). 

 In this case the sulphuretted hydrogen may be regarded as first 

 being decomposed into the two constituents sulphur and hydrogen, 

 each of which then burns, uniting with the oxygen of the air to 

 form sulphur dioxide and water vapour respectively ; thus afford- 

 ing an illustration of an action of double combination (Chapter I. ). 



Expt. 243. Combustion of Carbon Bisulphide. Carbon di- 

 sulphide is a volatile bad-smelling fluid consisting of carbon united 

 with sulphur ; it burns readily with a pale flame like that of a 

 spirit lamp, producing as the result of the combustion carbon 

 dioxide and sulphur dioxide gases. As in the last experiment, the 

 substance may be regarded as being first split up into its consti- 



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