58 CHEMISTR V FOR A GRICUL TURAL S TU DENTS 



their great malleability and ductility and high conductivity for 

 heat and electricity. 



It is worthy of note that metals belonging to the same class are often 

 associated with each other in nature. Thus gold and silver are invariably 

 found together. Metals of weak chemical activity are usually found in 

 the free state, e.g. gold, silver, and platinum, and occasionally copper and 

 mercury. Metals of the other groups exist naturally in the combined state. 

 Of such metals many occur as oxides. Loadstone and haematite, emery, 

 tinstone, and pyrolusite are oxides of iron, aluminium, tin, and manganese 

 respectively. 



Physical Properties of the Metals. — Metals are distinguished from 

 non-metals in their power of forming alloys with each other. This renders 

 it possible to impart to a metal the colour, permanence, hardness, tenacity, 

 etc., which is required. Thus brass — an alloy of copper and zinc which 

 has the permanence of copper — is more useful because much harder. The 

 following are the constituents of some of the principal alloys : — 



British gold coin — gold, 22 ; copper 2 (22 " carat'* gold, pure gold being 

 24 carat). 



British silver coin — silver, 925 ; copper, ^^. 



British bronze coin — copper, 95 ; tin, 4 ; zinc, I. 



Brass — copper, 2 ; zinc, i. 



Aluminium gold — copper, 9; aluminium, i. 



Pewter — tin, i ; lead, i. 



Britannia metal — tin, 84 ; antimony, 10 ; copper, 4 ; bismuth, 2. 



Type metal — lead, 75 ; antimony, 20 ; tin, 5. 



Gun metal — copper, 9 ; tin, i. 



Common solder — tin, i ; lead, 2. 



An amalgam is an alloy with mercury. 



The force of attraction that causes the cohesion of particles is exhibited 

 to a different extent in different metals. When the cohesion is small, as in 

 antimony and bismuth, the metals are brittle ; when great, as in gold and 

 silver, the metals are tenacious, malleable, or ductile. One grain of gold, 

 the most malleable of all metals, can be beaten out into 56 square inches of 

 gold leaf. One grain of silver, one of the most ductile of metals, can be 

 drawn into 500 feet of wire. This cohesive force in metals is measured by 

 the breaking strain. 



Metals as a rule are good conductors of heat, but they differ in their 

 conductivity. If upon one end of rods of several different metals a small 

 piece of wax or phosphonis be placed, and the other end be heated, the 

 heat will be conducted from one end to the other, as shown by the melting 



