hydroxyl radicle (HO), which is also expressed in the analogy existing between chlorine, Cl 2 , and hydrogen peroxide, (HO) 2 .
As regards the chloranhydrides corresponding to acids and non-metals, they bear but little resemblance to metallic salts. They are nearly all volatile, and have a powerful suffocating smell which irritates the eyes and respiratory organs. They react on water like many anhydrides of the acids, with the evolution of heat and liberation of hydrochloric acid, forming acid hydrates. For this reason they cannot usually be obtained from hydrates—that is, acids—by the action of hydrochloric acid, as in that case water would be formed together with them, and water decomposes them, converting them into hydrates. There are many intermediate chlorine compounds between true saline metallic chlorides like sodium chloride and true acid chloranhydrides, just as there are all kinds of transitions between bases and acids. Acid chloranhydrides are not only obtained from chlorine and non-metals, but also from many lower oxides, by the aid of chlorine. Thus, for example, CO, NO, NO2, SO2, and other lower oxides which are capable of combining with oxygen may also combine with a corresponding quantity of chlorine. Thus COCl2, NOCl, NO2Cl, SO2Cl2, &c., are obtained. They correspond with the hydrates CO(OH)2, NO(OH), NO2(OH), SO2(OH)2, &c., and to the anhydrides CO2, N2O3, N2O5, SO3, &c. Here we should notice two aspects of the matter: (1) chlorine combines with that with which oxygen is able to combine, because it is in many respects equally if not more energetic than oxygen and replaces it in the proportion Cl2: O; (2) that highest limit of possible combination which is proper to a given element or grouping of elements is very easily and often attained by combination with chlorine. If phosphorus gives PCl3 and PCl5, it is evident that PCl5 is the higher form of combination compared with PCl3. To the form PCl5, or in general PX5, correspond PH4I, PO(OH)3, POCl3, &c. If chlorine does not always directly give compounds of the highest possible forms for a given element, then generally the lower forms combine with it in order to reach or approach the limit. This is particularly clear in hydrocarbons, where we see the limit CnH2n+2 very distinctly. The unsaturated hydrocarbons are sometimes able to combine with chlorine with the greatest ease and thus reach the limit. Thus ethylene, C2H4, combines with Cl2, forming the so-called Dutch liquid or ethylene chloride, C2H4Cl2, because it then reaches the limit CnX2n+2. In this and all similar cases the combined chlorine is able by reactions of substitution to give a hydroxide and a whole series of other derivatives. Thus a hydroxide called glycol, C2H4(OH)2, is obtained from C2H4Cl2.
Chlorine in the presence of water very often acts directly as an oxidising agent . A substance A combines with chlorine and gives, for example, ACl 2 , and this in turn a hydroxide, A(OH) 2 , which on losing water forms AO. Here the chlorine has oxidised the substance A. This frequently happens in the simultaneous action of water and chlorine: A + H 2 O + Cl 2 = 2HCl + AO. Examples of this oxidising action of chlorine may frequently be observed both in practical chemistry and technical processes. Thus, for instance, chlorine in the presence of water oxidises sulphur and metallic sulphides. In this case the sulphur is converted into sulphuric acid, and the chlorine into hydrochloric acid, or a metallic chloride if a metallic sulphide be taken. A mixture of carbonic oxide and chlorine passed into water gives carbonic anhydride and hydrochloric acid. Sulphurous anhydride is oxidised by chlorine in the presence of water into sulphuric acid, just as it is by the action of nitric acid: