482 PRINCIPLES OF CHEM1STRT 



Part of the salt namely, two-thirds of it parts with its oxygen in 

 order to oxidise -the remaining third. 36 From an intermediate sub- 

 stance, RX, two extremes, R and RX 3 are formed, just as nitrous 

 anhydride splits up into nitric oxide and nitric anhydride (or nitric 

 acid). The resulting salt, MC10 3 , corresponds with chloric acid and 

 potassium chlorate, KC1O 3 . It is evident. that a similar saft may be 

 obtained directly by the action of chlorine on an alkali if its solu- 

 tion be heated, because RC1O will be first formed, and then RC1O 3 ; 

 for example, 6KHO + 3C1 2 = KC10 3 + 5KC1 + 3H 2 O. Chlorates 

 are so prepared ; for instance, potassium chlorate, which is easily 

 separated from potassium chloride, being sparingly soluble in cold 

 water. 37 



56 Hydrochloric acid, which is an example of compounds of this kind, is a satu- 

 rated substance which does not combine directly with oxygen, but in which, nevertheless, 

 a considerable quantity of oxygen may be inserted between the elements forming it. 

 The same may be observed in a number of other cases. Thus oxygen may be added 

 or inserted between the elements, sometimes in considerable quantities, in the saturated 

 hydrocarbons ; for instance, in C 5 H 8 , three atoms of oxygen produce an alcohol, glycerin 

 or glycerol, C 5 H S (OH) 3 . We shall meet with similar examples hereafter. This is 

 generally explained by regarding oxygen as a bivalent element that is, as capable of 

 combining with two different elements, such as chlorine, hydrogen, &c. On the basis of 

 this view, it may be inserted between each pair of combined elements ; the oxygen will 

 then be combined with one of the elements by one of its affinities and with the other 

 element by its other affinity. This view does not, however, express the entire truth 

 of the matter, even when -applied to the compounds of chlorine, Hypochlorous acid, 

 HOC1 that is, hydrochloric acid in which one atom of oxygen is inserted is, as we have 

 already seen, a substance of small stability ; it might therefore be expected that on the 

 addition of a fresh quantity of oxygen, a still less stable substance would be obtained, 

 because, according to the above view, the chlorine and hydrogen, which form such a 

 stable compound together, are then still further removed from each other. But it appears 

 that chloric and perchloric acid, HC1O 3 and HC1O 4 , are much more stable substances. 

 Furthermore, the addition of oxygen has also its limit, it can only be added to a certain 

 extent. If the above representation were true and not merely hypothetical, there 

 would be no limit to the combination of oxygen, and the more it entered into one continuous 

 chain the more unstable would be the resultant compound. But not more than four 

 atoms of oxygen can be added to hydrogen sulphide, nor to hydrochloric acid, nor to 

 hydrogen phosphide. This peculiarity must lie in the properties of oxygen itself ; four 

 atoms of oxygen seemj have the power of forming a kind of radicle which retains two 

 or several atoms of various other substances for example, chlorine and hydrogen, 

 hydrogen and sulphur, sodium and manganese, phosphorus and metals, &c., forming 

 comparatively stable compounds, NaClO 4 , Na2SO 4 , NaMnO 4 , Na5PO 4 , &c. See Chapter X. 

 Note 1 and Chapter XV. 



57 If chlorine be passed through a cold solution of potash, a bleaching compound, 

 potassium chloride and hypochlorite, EC1 + EC1O, is formed, but if it be passed through 

 a hot solution potassium chlorate is formed. As this is sparingly soluble in water, it 

 chokes the gas-conducting tube, which should therefore be widened out at the end. 



Potassium chlorate is usually obtained on a large scale from calcium chlorate, which 

 is prepared by passing chlorine (as long as it is absorbed) into water containing lime, the 

 mixture being kept warm. A mixture of calcium chlorate and chloride is thus formed 

 in the solution. Potassium chloride is then added to the warm solution, and on cooling 

 a precipitate of potassium chlorate is formed as a substance which is sparingly soluble in 



