402 



SCIENTIFIC RECREATIONS. 



which is quickly tarnished. Silver is often present in lead ore, and is 

 extracted by Pattison's process, which consists in the adaptation of the 



knowledge that lead containing silver 

 becomes solid, after melting, at a 

 lower temperature than lead does when 

 pure. Pure lead therefore solidifies 

 sooner. 



One great use of lead is for our 

 domestic water-pipes, which remind us 

 in winter of their presence so disagree- 

 ably. Shot is made from lead, and 

 bullets are cast from the same metal. 

 Shot-making is very simple, and before 

 the days of breech-loading guns and 

 cartridges, no doubt many readers have 

 cast bullets in the kitchen and run 

 them into the mould over a basin of 

 water or a box of sand. For sporting 

 purposes lead is mixed with arsenic, 

 and when it is melted it is poured 

 through a sort of sieve (as in the cut) 

 at the top of a high tower. (See figs. 

 I an( ^ The latter illustration 



Fig. 4 i2.-shot tower. 



gives the section of the shot tower ; A is the furnace, B is the tank 

 for melting the lead, and the metal is permitted by the workman at c to 

 run through the sieve in fine streams. As the lead falls it congeals into 

 drops, which are received in water below to cool them. They are, of course, 

 not all round, and must be sorted. This operation is performed by placing 

 them on a board tilted up, and under which are two boxes. The round 

 shot rush over the first holes and drop into the second box, but the uneven 

 ones are caught lagging, and drop into box No. I. They are accordingly 

 sent to the furnace again. 



The next process is to sort the good shot for size. This is done by 



sieves O ne having holes a little larger than 

 the size of shot required. This sieve passes 

 through it all of the right size and smaller, 

 and keeps the bigger ones. Those that have 

 passed this examination are then put into 

 Fig. 4i3-sieve for making S hot. anot her sieve, which has holes in it a little 

 smaller than the size of shot wanted. This sieve retains the right shot, 

 and lets the smaller sizes pass, and so on. The shot are sized and num- 

 bered, glazed by rolling them in a barrel with graphite, and then they are 

 ready for use. Bullets are made by machinery by the thousand, and made 

 up into cartridges with great speed. 



The compounds of lead are also poisonous, and produce " colic," to 



