484 PRINCIPLES OF CHEMISTRY 



(and consequently with KC10 3 also) acting in the same manner as it 

 acts on the lower acids : HC10 3 + 5HC1 = 3H 2 O + 3C1 2 . 



By cautiously acting on potassium chlorate with sulphuric acid, the 

 diootide (chloric peroxide), C10 2 , 39 is obtained (Davy, Millon). This gas 

 is easily liquefied in a freezing mixture, and boils at -t- 10. The 

 vapour density (about 35 if H = 1) shows that the molecule of this 

 substance is C10 2 . 40 In a gaseous or liquid state it very easily explodes 

 (for instance, at 60, or by contact with organic compounds or finely 

 divided substances, &c.), forming Cl and O 2 , and in many instances 41 

 therefore it acts as an oxidising agent, although (like nitric peroxide) 

 it may itself be further oxidised. 42 In dissolving in water or alkalis 

 chloric peroxide gives chlorous and hypochlorous acids 2C10 2 -f 2KHO 

 as KC10 3 + KC10 2 + H 2 and therefore, like nitric peroxide, 

 the dioxide may be .regarded as an intermediate oxide between the 

 (unknown) anhydrides of chlorous and chloric acids : 4C10 2 = C1 2 8 



+ ci 2 cv 3 



As the salts of chloric acid, HC10 3 , are produced by the splitting 

 up of the salts of hypochlorous acid, so in the same way the salts of 



39 To prepare C10 2 100 grams of sulphuric acid are cooled in a mixture of ice and 

 salt, and 15 grains of powdered potassium chlorate are gradually added to the acid, which 

 is then carefully distilled at 20 to 40, the vapour given off being condensed in a- 

 freezing mixture. Potassium perchlorate is then formed: 8KC10 3 +2H 2 S0 4 =2KHSO4 

 + KC104+2C1O 2 + H2O. The reaction may result in an explosion. Calvert and Da vies 

 obtained chloric peroxide .without the least danger by heating a mixture of oxalic 

 acid and potassium chlorate in a test tube in a water-bath. In this case 2KC1C>3 

 + 3C 2 H 2 4 2H 2 O = 2C 2 HKO 4 + 2CO 2 + 2C1O 2 + 8H<jO. The reaction is still further f acili. 

 fcated by the addition of a small quantity of sulphuric acid. If a solution of HC1 acta 

 upon KC10 3 at the ordinary temperature, a mixture of C1 2 and C10 2 is formed, but if the 

 temperature be raised to 80 the greater part of the C1O 2 decomposes, and when passed 

 through a hot solution of MnCL it oxidises it. Gooch and Kreider proposed (1894) to 

 employ this method for preparing small quantities of chlorine in the laboratory. 



40 By analogy with nitric peroxide it might be expected that at low temperatures a 

 doubling of the molecule into C1 2 O 4 would take place, as the reactions of C1O 2 point to 

 its being a mixed anhydride of HC1O 2 and HC10 3 . 



41 Owing to the formation of this chlorine dioxide, a mixture of potassium chlorate 

 and sugar is ignited by a drop of sulphuric acid. This property was formerly made 

 use of for making matches, and is now sometimes employed for setting fire to explosive 

 charges by means of an arrangement in which the acid is caused to fall on the mixture 

 at the moment required. An interesting experiment on the combustion of phosphorus 

 under water may be conducted with chlorine dioxide. Pieces of phosphorus and of 

 potassium chlorate are placed under water, and sulphuric acid is poured on to them 

 (through a long funnel) ; the phosphorus then burns at the expense of the chlorine 

 dioxide. 



** Potassium permanganate oxidises chlorine dioxide into chloric acid (Fiirst). 



** The euchlorine obtained by Davy by gently heating potassium chlorate with hydro- 

 chloric acid is (Pebal) a mixture of chlorine dioxide and free chlorine* The liquid and 

 gaseous chlorine oxide (Note 85), which Millon considered to be C1 2 O 3 , probably contains 

 a mixture of CIO;, (vapour density 35), C1 2 3 (whose vapour density should be 59), and 

 chlorine (vapour density 85'5), since its vapour density was determined to be about 40. 



