24 SCIENTIFIC AMUSEMENTS. 



a crucible or ladle and then pour the melted metal into a tub of 

 cold water from as great a height as possible, conveniently by 

 standing on a step ladder. As the melted zinc comes in contact 

 with the water it becomes suddenly chilled, and forms thin pieces 

 often of peculiar shape, and much more bulky than the original 

 lumps of metal. Finally the granulated zinc is drained from the 

 water, dried on a towel and by exposure to the air in a thin 

 layer on a newspaper, and bottled for future use in various 

 chemical experiments, more especially those where hydrogen gas is 

 required (Expts. 10, 104, and subsequent ones). 



Tin, lead, and various other metals can be granulated in the 

 same way. 



Expt. 17. To make Explosive Glass Drops. In order to melt 

 glass a sound crucible, capable of standing a high temperature, is 

 indispensable, as well as a fire with a good draught so as to heat 

 the crucible sufficiently. If the glass is thoroughly melted and 

 then dropped into water it frequently does not fly about and 

 granulate as melted metal does, but the drops solidify into solid 

 pear-shaped lumps with long thin tails. Glass thus quickly cooled 

 possesses the peculiar property that the pear-shaped end will stand 

 a pretty heavy blow without breaking ; but if the thin end be 

 broken off or even scratched, the whole crumbles to powder. At 

 the instrument dealers these glass drops may be purchased under 

 the name of " Prince Rupert's drops," it being supposed that 

 Prince Kupert first observed the peculiarity of glass thus treated. 



Of late years glass articles have been sold said to be " tough- 

 ened" by rapidly cooling them in water, or better in oil, after 

 they have been worked into shape whilst hot; such toughened 

 glass will often resist a wonderful amount of hard usage without 

 breaking; but sometimes a slight scratch will cause the whole 

 article to shiver to fragments like a Prince Rupert's drop; for 

 which reason " toughened glass " has not come so extensively into 

 use for household and other purposes as might have been expected 

 from its diminished fragility in ordinary wear and tear. 



Expt. 18. To Crystallise Metals by Melting. If you try to 

 break across a properly cast rod of lead prepared as in Expt. 15, 

 you will find that it will bend sooner than break, lead being a 

 soft metal not brittle when cast ; but if you try to bend a thin 

 rod of zinc cast in the same way you will find that the rod will 

 snap in two sooner than bend, because cast zinc is not soft and 

 flexible, but somewhat brittle. On examining the broken surfaces 

 of the fractured rod you will notice that they are bright and shin- 

 ing, cast zinc being what is termed crystalline. Some kinds of 

 metals crystallise very finely when they are melted and allowed to 



