512 SMITH'S INTERMEDIATE CHEMISTRY 



stills, and evaporating pans are made of copper. It is used for 

 sheathing ships and for bolts, because it resists corrosion by sea 

 water. 



It enters into important alloys, such as brass (18 to 40 per cent 

 of zinc), and bronze for coins (4 per cent tin and 1 per cent zinc), 

 for gun-metal (10 per cent tin), and for bell-metal (20 to 24 per 

 cent tin). Aluminium bronze (5 to 10 per cent aluminium) is used 

 for the hulls of yachts. All of these are composed in part of com- 

 pounds, such as Cu 3 Sn and Cu 2 Zn 3 . 



Cupric Sulphate CuSO 4 ,5H 2 O. The hydrated sulphate, 

 bluestone or blue vitriol, is made by continuously agitating granu- 

 lated copper with air and warm dilute sulphuric acid : 



2Cu + O 2 + 2H 2 S0 4 -> 2CuSO 4 + 2H 2 O. 



The blue crystals form on strips of lead suspended in the warm, 

 saturated solution. 



Because of slight hydrolysis, giving an active acid and a weak 

 base Cu(OH) 2 , the aqueous solution is acid in reaction. 



Cupric sulphate is used in battery solutions. The salt is em- 

 ployed in minute proportions to destroy algae, which otherwise 

 confer a disagreeable taste and odor on water that has been stand- 

 ing in reservoirs. Seed for cereals is moistened with a dilute solu- 

 tion to prevent " smuts." 



Cupric Hydroxide Cu(OH) 2 . The hydroxide is a blue, 

 gelatinous precipitate, formed when an alkali is added to cupric 

 sulphate solution. It is used as a mordant. A mixture of cupric 

 sulphate solution and milk of lime (Ca(OH) 2 ), Bordeaux mix- 

 4u% containing this precipitate, is used extensively as a spray 

 on grape vines and other plants, to prevent the growth of fungi. 



Cupric hydroxide dissolves in ammonium hydroxide solution, 

 giving a liquid of deep blue color. The explanation of this, accord- 

 ing to the ionic hypothesis, is as follows. The solubility product 



