EXAMINATION OF COMMON SUBSTANCES 99 



Blue vitriol in solution with lime or soda is used as a fungicide for 

 spraying potato plants and fruit trees. It is also used in electroplating, 

 and in certain electric batteries. 



40. EXAMINATION OF SAL AMMONIAC. 



i. Examine as described in Chapter XVTI. 



Sal ammoniac. Sal ammoniac is a white crystalline powder. It has 

 a taste rather like salt, but not so pleasant. It is very soluble in water. 

 When heated it does not melt, but is converted into a vapour, from 

 which the solid is re-formed higher up on the cooler parts of the test- 

 tube. A solid which on heating changes from a solid to a vapour, 

 without becoming liquid, is said to sublime. The process is called 

 sublimation. 



Sal ammoniac is used for charging Leclanche cells. It is also used 

 as a flux in soldering and in the making of galvanized iron. 



41. EXAMINATION OF GREEN VITRIOL. 



i. Examine as described in Chapter XVII. 



Green vitriol. Green vitriol is a green crystalline solid. It has a 

 peculiar taste rather like ink (of which it is a constituent). It dis- 

 solves in water, forming a pale green solution which soon turns 

 yellowish. On gently heating a crystal of it becomes a whitish colour 

 and gives off water. When strongly heated it turns to a dark red 

 colour and sharp smelling fumes are given off. The action of heat on 

 green vitriol will be studied more fully later, Chap. XXIII. 



42. EXAMINATION OF WASHING SODA. 



i. Examine as described in Chapter XVII. 



ii. Effect of exposure in air. Wash a large crystal of soda with distilled 

 water, dry with filter paper and leave it on a watch-glass in the open 

 laboratory. Examine next class day. 



iii. Water of crystallisation. Find the percentage of water of crystal- 

 lisation in soda. 



iv. Effect of strong heating Try the effect of (a) strong heating and (/>) 

 water on the residue from iii. 



Washing soda. Washing soda is a transparent crystalline solid, with 

 a bitter taste. It is very soluble in water, and the solution turns red 

 litmus blue. When left exposed in ah 1 it loses its crystalline appearance 

 and becomes coated with a white powder. The same effect can be 



