380 SMITH'S INTERMEDIATE CHEMISTRY 



or two of concentrated sulphuric acid to the residue. If the 

 specimen now gives a yellow gas (nitrous anhydride), the original 

 substance was a nitrate (of K or Na), from which the nitrite was 

 formed by heating (p. 311). If it gives a colorless, fuming gas 

 (HC1), the original substance was a chlorate (p. 30). 



Examination of a Liquid. Test the specimen with litmus 

 paper. A marked acid reaction may be due to an acid, such as 

 concentrated or dilute sulphuric acid (p. 270), concentrated or 

 dilute nitric acid (p. 309), concentrated or dilute hydrochloric 

 acid (p. 131), hydrobromic acid (p. 202), hydriodic acid (p. 205), 

 phosphoric acid (p. 322), sulphurous acid (p. 259), or an organic 

 acid (p. 348); also an acid-salt (p. 192), or a hydrolyzed salt (p. 

 369). 



If it bleaches litmus paper, it may be chlorine-water or bromine- 

 water (odor). 



If it is markedly alkaline in reaction, it may be a solution 

 of a base (NaOH, KOH, NH 4 OH, etc.) or a hydrolyzed salt (p. 

 355). 



Note the odor. Ammonium hydroxide, hydrogen sulphide solu- 

 tion, sulphurous acid, concentrated nitric acid and concentrated 

 halide acids all have odors. Alcohol, acetic acid, carbon disul- 

 phide, carbon tetrachloride, and hydrocarbons (e.g. gasoline) 

 have odors easily distinguished from those of the foregoing. 



Evaporate a few drops to dryness on a watch crystal. A solid 

 residue shows that the original substance was a solution in 

 water (or possibly alcohol or some other solvent, if the vapor has an 

 odor indicating this). If there is a solid residue, a quantity of it 

 may be obtained by evaporating a larger amount of the liquid, 

 and may then be treated as a solid (pp. 377-9). 



If the specimen leaves no residue, and is not acid or alkaline 

 but has an odor, it may be one of the volatile organic compounds 

 named above. If it is odorless, it may be a solution of hydrogen 

 peroxide (p. 222) or simply pure water. 



