CARBON MONOXIDE. 199 



plicated; first, the sulphuric acid and sodium formate act on one 

 another by double decomposition in such a way as to form a sub- 

 stance termed " acid sulphate of sodium," together with a volatile 

 acid body closely akin to vinegar, and known us formic acid; and 

 then this formic acid becomes decomposed into water vapour or 

 steam and carbon monoxide which comes off as a gas. 



Expt. 220. To show that Carbon Monoxide forms Carbon 

 Dioxide on burning. Collect a small jar of carbon monoxide, 

 remove the saucer, and apply a light (whether the jar is held 

 mouth downwards or upwards is of but little consequence); the 

 gas will burn with a blue flame if pure, not giving out much 

 light. Quickly place the jar on the table, mouth upwards, and 

 pour in some limewater ; close the jar with the palm of the hand 

 or with a cork, and shake up; the limewater will be turned 

 milky, showing that carbon dioxide is now present (Expt. 152). 

 In this case gaseous carbon monoxide and gaseous oxygen have 

 united to form gaseous carbon dioxide, so that no change of state 

 has occurred on the whole. 



Expt. 221. Explosive Nature of Mixtures of Carbon Mon- 

 oxide and Oxygen. Collect in a soda-water bottle some carbon 

 monoxide (as in Expt. 208), until about two-thirds of the water 

 present in the bottle are displaced ; then fill it with oxygen, so that 

 the mixture of gases present will be approximately two volumes of 

 carbon monoxide and one of oxygen. Apply a light to the mouth 

 of the bottle, and a tolerably loud report will ensue. It is as well 

 to wrap a towel round the bottle first, to avoid danger from 

 splintered glass should the bottle break. After the explosion, 

 quickly pour into the bottle some limewater and shake up as in 

 the last experiment; the limew T ater will be rendered milky by 

 the carbon dioxide formed. 



Expt. 222. To prepare Nitric Oxide Gas. Into a gas generator 

 (fig. 56) introduce some copper turnings, and then pour diluted 

 nitric acid down the funnel; the acid will speedily act on the 

 copper, dissolving it and evolving a gas termed nitric oxide (Expt. 

 116) different from the nitrous oxide or laughing gas obtained in 

 Expt. 187. When the air has been all expelled from the apparatus 

 the gas may be collected over water in the pneumatic trough. 



Expt. 223. To produce Red Fumes by combining Nitric 

 Oxide and Oxygen. Nitric oxide is, when pure, a colourless gas, 

 but when brought into contact with oxygen the two gases com- 

 bine to form a red coloured gas differing from either, especially 

 in being much more soluble in water. When nitric acid comes 

 in contact with copper (as in Expt. 222), red fumes are at 

 first visible; these arise from the action of the nitric oxide first 



