66 



SCIENTIFIC AMUSEMENTS. 



as when moist air is chilled ; just as the cooler air is incapable of 

 retaining intermixed with it all the water-vapour at first present, 

 so that the surplus deposits as liquid water, forming mist or dew 

 (Chapter III.) ; so a hot saturated solution, when allowed to cool, 

 allows some of the dissolved solid to reappear in the solid form, 

 generally in the form of crystals of larger or smaller size according 

 to circumstances ; these crystals have usually a tendency to deposit 

 on any foreign solid body placed in the cooling fluid, so as to coat 

 it over with little crystallised masses. 



Boil some water in a small saucepan, and add sugar to it as long 

 as any dissolves, taking care not to burn the syrup. Lay some 

 pieces of stick across the saucepan with bits of string hanging 

 down from them so as to dip into the syrup ; or put thin bits of 

 stick into the pan, so as to stand nearly upright. Now leave the 

 whole at rest for 24 .hours ; at the end of this time the strings 

 and immersed sticks will be coated over with crystals of sugar, 

 forming sugar candy ; by leaving these in the syrup some days 

 longer, the crystals will gradually grow larger. 



Sugar that has been overheated, or brownish imperfectly puri- 

 fied sugar (containing treacle, &c.), generally requires a longer time 

 to deposit crystals than pure white loaf-sugar, as the products of 

 the action of heat on the sugar, and the other impurities, have the 

 power of stopping more or less the separation of solid crystals from 



the solution. Crystal- 

 lised fruits are made by 

 steeping dried fruits in 

 syrup, so that sugar crys- 

 tals form all over them. 



Expt. 59. To make 

 Crystallised Baskets. 

 Very pretty objects may 

 be made by placing 

 wicker-work baskets or 

 skeleton figures, such as 

 a crown made of wire 

 lapped over with cotton 

 or wick, in a saturated 

 solution of alum in hot 

 water and allowing to 

 stand for some days ; the 

 alum separates in well- 

 defined crystals all over 

 the surface, the crystals so formed growing larger the longer they 

 are left immersed, because the water slowly evaporates. Fig. 38 



Fig. 38. Alum Crystals. 



