LESSONS IN CHEMISTRY. 157 



glazing cards, etc. Barium chloride, BaCl 2? is much used in lab- 

 oratory work as a test for the presence of sulphuric acid. Barium 

 compounds give a yellowish green flame. 



STRONTIUM is less abundant than barium and is of little interest. 

 It occurs in nature chiefly as the mineral celestine which is the 

 strontium nitrate. This salt gives a bright red color to flames, 

 and is often used in the preparation of fire works. 



MAGNESIUM (Mg) is a silver white metal. It burns at a low 

 temperature with a brilliant white light, which may be used to 

 illuminate objects for photographing. It is widely distributed 

 in nature as an ingredient of dolomite or magnesian limestone, 

 soapstone, asbestos, horenblend and talc. Most of these min- 

 erals have a soapy feel. Magnesium sulphate MgS0 4 H-7H 2 is 

 the epsom salts of the shops, and the oxide is the common mag- 

 nesia. When dolomite is burned it becomes what is called water 

 lime, which makes a mortar that will harden under water. 



ZINC (Zn) is a bluish white metal of a crystalline structure, 

 light, easily fusible, but not easily corroded by atmospheric 

 influences. The strength of iron and durability of zinc are com- 

 bined in the so-called galvanized iron, which is made by dipping 

 well cleaned iron in melted zinc, much as tin plate is made. Zinc 

 is an ingredient of brass and German silver. 



Zinc oxide is used in painting as zinc white, and zinc sulphate 

 (ZnS0 4 -h7H 2 0) is used in calico printing and to some extent in 

 medicine as white vitriol. Zinc is easily attacked by acids, and 

 the chemical action of acids on zinc is the most common source 

 of the galvanic current. Zinc precipitates lead, copper and silver 

 from solutions. A very interesting experiment is to place a strip 

 of zinc in a solution of acetate of lead. The lead quickly begins 

 to collect on the zinc forming what is called the lead tree. Zinc 

 occurs in nature most abundantly as the carbonate and as the 

 sulphide, which is the black jack of the lead miner. 



