FORMATION OF ACIDS. 207 



iron stand so as to wet the paper thoroughly with the liquid. 

 The carbon disulphide, being highly volatile, will soon evapo- 

 rate leaving a film of phosphorus on the paper; this will soon 

 begin to emit fumes, and by and by will burst into flame. The 

 popular term " Fenian fire " is derived from the reputed use of 

 this liquid by the Fenians for the purpose of setting fire to houses, 

 &c., by throwing in through the window or down a chimney a 

 bottle full of the phosphorus solution, so that the bottle might 

 break and thus cover carpets, curtains, bedclothes, &c., with 

 phosphorus solution which would speedily set them on fire. 



Caution. On account of its tendency to produce spontaneous 

 inflammation when the carbon disulphide evaporates, this liquid 

 is highly dangerous to keep; it should only be prepared in small 

 quantity, and when done with any left over from the experiment 

 should be poured away on the ground in the open air so as to 

 obviate the risk of fire. 



Production of Acids by Combustion. 



Shortly after the discovery of oxygen it was noticed that when 

 such substances as sulphur and phosphorus are burned therein 

 and the products of combustion dissolved in water, acid fluids 

 were obtained (Expts. 225 and 234), neutralising alkalies and red- 

 dening certain vegetable colours, such as litmus. Accordingly the 

 term oxygen was applied to the gas (from 6vs = acid and y/vaw = I 

 produce), it being supposed that it was indispensable to the 

 formation of acids. Later experiments have shown that this was 

 an incorrect idea and that the name is consequently a misnomer ; 

 because, firstly, the substances formed when sulphur and phos- 

 phorus, &c., are burnt in oxygen are not themselves acids, but only 

 become so on further combination with ivater; secondly, many 

 other substances such as magnesium, iron, and zinc (Expts. 231, 

 232, 233) when burnt in oxygen do not form acids, even on further 

 addition of water; and thirdly, because acids exist containing no 

 oxygen, e.g., hydrochloric acid, which consists of hydrogen and 

 chlorine only. 



Expt. 238. To prepare Sulphurous Acid Into a bottle of 

 oxygen introduce a ladle with a little burning sulphur, as in Expt. 

 225; when the sulphur has burnt away quickly introduce a wine- 

 glassful of distilled water, cork the bottle, and shake up well; 

 the water will dissolve the gas (sulphur dioxide) formed by the 



is not prone to spontaneous combination with the oxygen of the air and 

 consequently taking fire, so that it may be kept in an ordinary bottle or box 

 freely exposed to the air without inflaming. 



