378 SMITH'S INTERMEDIATE CHEMISTRY 



dicates an acid-salt (p. 192), an easily hydrolyzed salt (e.g. FeCl 3 , 

 6H 2 0) or organic acid. Continue heating, inclining the tube 

 mouth downwards, removing condensed water with filter paper 

 until no more comes off, and heat the residue. 



A gas is given off. The gas may be violet (some iodides) or 

 brown (some nitrates, p. 311, and some bromides). If brown, 

 lower a glass rod dipped in silver nitrate solution into the gas 

 in the tube. Bromine will give a white precipitate (AgBr, p. 

 202). In case of a negative result try the test for nitrates. 



The gas may be colorless. If it has an odor, it may be am- 

 monia from a salt of ammonium, sulphur dioxide from a bisulphite 

 (p. 258) or from oxidation of a sulphide (p. 258). A stifling odor 

 with fumes may be sulphur trioxide from some sulphates or de- 

 composition products from some organic matters. 



The gas is colorless and odorless. It may be oxygen (test with 

 long, glowing splinter of wood) from a peroxide, chlorate, or ni- 

 trate (of K or Na). To learn which of these it is, dissolve or sus- 

 pend a little of the substance in water, add dilute sulphuric acid, 

 and test for hydrogen peroxide (p. 223). In case of a negative 

 result examine the residue (as in p. 379). 



A colorless, odorless gas may be carbon dioxide, coming from a 

 bicarbonate or a carbonate (except of K or Na) . Lower a glass rod 

 dipped in lime-water into the gas in the test-tube (white precipi- 

 tate, CaCO 3 J,). 



The substance carbonizes or chars and gives an odor of smolder- 

 ing wood or burning flesh. The compound is organic. Identify, 

 by properties (pp. 346-50, 353). 



Heating may produce no effect. On the other hand, more than 

 one of these effects (e.g. both water and sulphur dioxide from a 

 bisulphite) may be given by the same specimens. 



If heating produces any effect, continue heating until all change 

 ceases, and preserve the residue for use in p. 379. 



In most cases other distinctive properties and tests will be 

 found on the pages referred to. 



