IN POPULAR CHEMISTRY. 99 



the cuprous and the cupric salts. The two oxides are com- 

 monly known as the red and the black. 



(8.) Phosphorus forms two oxides, phosphorous anhydride 

 (P 2 O 3 ) and phosphoric anhydride (P 2 O 5 ). 



39. Is charcoal lighter than H 2 O ? 



Charcoal appears at first sight to be lighter than water, as 

 a piece of it floats on the surface of this liquid ; this is, how- 

 ever, due to the porous nature of the charcoal, for if it be 

 finely powdered it sinks to the bottom of the water. ROSCOE. 



40. Name the.vitriols. 



The compounds of sulphuric acid, commonly called "the 

 vitriols," are as follows: 



1. Sulphate of iron, Green vitriol. 



2. Sulphate of copper, Blue vitriol. 



3. Sulphate of zinc, White vitriol. 



41. Is My univalent or bivalent ? Zn ? 



Mg belongs to the zinc class of metals which comprises 

 magnesium, zinc, cadmium, and indium. These are all bivalent. 



42. Name some dibasic acid. 



Sulphuric acid. 



43. Name a neutral salt. An acid salt. 



Sodium sulphate is neutral (Na 2 SO 4 ). Hydro-sodium sul- 

 phate is acid (HNaSOJ. 



44. Calculate the percentage of water contained in 

 crystallized copper sulphate. Sodium sulphate. Calcium 

 sulphate. Alum. 



(1.) CuSO 4 , 5H 3 O = 249.5. 

 5H 2 = 90. 



Hence, -$% = .36 = 36 % of copper sulphate is water. 



(2.) Na 2 SO 4 , 10H 2 O = 322. 

 10H 2 O = 180. 



Hence, iff = .55 = 55 % of sodium sulphate is water, 



