THE HALOGENS 483 



If dilute sulphuric acid be added to a solution of potassium chlorate, 

 chloric acid is liberated, but it cannot be separated by distilla- 

 tion, as it is decomposed in the process. To obtain the free acid, 

 sulphuric acid must be added to a solutio'n of barium chlorate. 3 * The 

 sulphuric acid gives a precipitate of barium sulphate, and free chloric 

 acid remains in solution. The solution may be evaporated under 

 the receiver of an air-pump. This solution is colourless, has no 

 smell, and acts as a powerful acid (it neutralises sodium hydroxide, 

 decomposes sodium carbonate, gives hydrogen with zinc, &c.) ; when 

 heated above 40, however, it decomposes, forming chlorine, oxygen, 

 and perchloric acid : 4HC1O 3 = 2HC1O 4 + H 2 O + C1 2 + O 3 . In a 

 concentrated condition the acid acts as an exceedingly energetic 

 oxidiser, so that organic substances brought into contact with it burst 

 into flame. Iodine, sulphurous acid, and similar oxidisable substances 

 form higher oxidation products and reduce the chloric acid to hydro- 

 chloric acid. Hydrochloric acid gas gives chlorine with chloric acid 



cold water, especially in the presence of other salts. The double decomposition taking 

 place is Ca(ClO 3 )._, + 2KC1 = CaClo + 2KC1O 3 . On a small scale in the laboratory potassium 

 chlorate is best prepared from a strong solution of bleaching powder by passing chlorine 

 through it and then adding potassium chloride. KClOs is always formed by the action 

 of an electric current on a solution of KC1, especially at 80 (Haussermann and Naschold, 

 1894), so that this method is now used on a large scale. 



Potassium chlorate crystallises easily in large colourless tabular crystals. Its solu- 

 bility in 100 parts of water at' = 3 parts, 20 = 8 parts, 40 = 14 parts, 60 = 25 parts, 

 80 = 40 parts. For comparison we will cite the following figures showing the solubility 

 of potassium chloride and perchlorate in 100 parts of water : potassium chloride at = 28 

 parts, 20==S5 parts, 40 = 40 parts, 100 = 57 parts; potassium perchlorate at about 

 1. part, 20 about If part, 100"^ about 18 parts. When heated, potassium chlorate melts 

 (the melting point has been given as from 335-376 ; according to the latest determination 

 by Carnelley, 359) and decomposes with the evolution of oxygen, potassium perchlorate 

 being at first formed, as will afterwards be described (see Note 47). A mixture of 

 potassium chlorate and nitric and hydrochloric acids effects oxidation and chlorination 

 in solutions. It deflagrates when thrown upon incandescent carbon, and when mixed 

 with sulphur (J by weight) it ignites it on being struck, in which case an explosion 

 takes place. The same occurs with many metallic sulphides and organic substances; 

 Such mixtures are also ignited by a drop of sulphuric acid. All these effects are due to the 

 large amount of oxygen contained in potassium chlorate, and to the ease with which it 

 is evolved. A mixture of two parts of potassium chlorate, one part of sugar, and one 

 part of yellow prussiate of potash acts like gunpowder, but bums too rapidly,, and 

 therefore bursts the guns, and it also has a very strong oxidising-action on their metal. 

 The sodium salt, NaClO 3 , is much more soluble than the potassium salt, and it? is 

 therefore more difficult to free it from sodium chloride, &c. The barium salt? 'is also" 

 more soluble than the potassium salt; = 24 parts, 20 = 87 parts, 80 = 98 parts' 6f salt 

 per 100 of water. 



38 Barium chlorate, Ba(ClO 3 ) 2 ,H 2 O, is prepared in the following way : impure chloric 

 acid is first prepared and saturated with baryta, and the barium salt purified by crystal- 

 lisation. The impure free chloric acid is obtained by converting the potassium in potas- 

 sium chlorate into an insoluble salt. This is done by adding tartaric or hydrofluosilicio 

 acid to a solution of potassium chlorate, because potassium tartrate and potassium silico- 

 fluoride are very sparingly soluble in water. Chloric acid is easily soluble in water. 



