236 



SCIENTIFIC AMUSEMENTS. 



into the air, they take fire spontaneously as they fall. Metals in 

 this condition are said to be pyrophoric. 



Thus, at the ordinary temperature solid lead does not combine 

 quickly with oxygen, especially if perfectly dry ; but when 

 obtained as pyrophoric metal, it takes fire instantly on coming in 

 contact with the air. To obtain pyrophoric lead add a solution 

 of tartaric acid to one of sugar of lead (lead acetate) ; a heavy 

 precipitate^ of lead tartrate will fall down, which may be washed 

 by decantation (Expt. 120) in a basin, and then dried over a 

 steam bath (Expt. 89). If lumps have formed by clotting 

 together, powder them, and introduce the powder into a long 

 glass tube corked at one end, or (better still) drawn out and closed 

 by melting together the drawn out portions (Expt. 48). Cautiously 

 heat the tube and contents with one or more Bunsen lamps, 

 commencing at the sealed-up end ; the tartrate of lead will be 

 decomposed by the heat (somewhat as coal, &c., in Expts. 200, 

 201, 202), gases being evolved and metallic lead in a fine state of 

 division being formed. When gases cease to come off, the open 

 end of the tube must be tightly corked up (or better still " her- 

 metically sealed" by drawing out and fusing together like the 

 other end) and the whole allowed to cool. On opening the tube 

 and shaking out the powder contained, a shower of sparks will be 

 produced, which will be still more brilliant if the particles are 

 allowed to fall into a jar of oxygen. 



Many other metals can be obtained in the pyrophoric form by 



somewhat similar means. In Expt. 

 268, if very finely divided oxide 

 of copper be used and the hydro- 

 gen be made to act on it with as 

 little heating as possible, the par- 

 ticles of copper ultimately obtained 

 are often pyrophoric, especially if 

 shaken out of the tube before they 

 are quite cooled. Very finely pow- 

 dered oxides of iron and other 

 'metals treated in the same way 

 will often similarly furnish pyro- 

 phoric iron, &c. 



Expt. 283. To keep Wire Bed 

 hot by Means of Coal Gas with- 

 out Flame. Obtain a piece of 

 thin platinum wire some 15 or 

 18 inches long, and coil up round a pencil all but 1 or 2 inches 

 (fig. 97). Light a Bunsen gas burner and hold in the flame the 



Fig. 97. Platinum Spiral and 

 Bunsen burner. 



