58 SCIENTIFIC AMUSEMENTS. 



case of brimstone or sulphur, when heated to boiling, if the 

 vapour is allowed to condense on a surface heated above the 

 melting-point of sulphur (about 111 C.) it condenses as liquid 

 brimstone which runs down, just as water would do on distillation. 

 If the surface is below this temperature, the sulphur condenses as 

 small solid crystals, just like hoarfrost ; whilst if sulphur vapour 

 is quickly chilled, it solidifies to " flowers of sulphur," partly 

 crystallised like fine snow and partly consisting of minute spheri- 

 cal particles or utricles, resembling miniature hail. 



Sublimation. 



Some few solids on heating pass directly into the vaporous con- 

 dition, and, vice versa, their vapours condensing directly to solids 

 without liquefying previously. When a solid is heated so that its 

 vapours condense again in a different part of the apparatus, the 

 process is termed sublimation, being to the solid exactly what 

 distillation is to a liquid. 



Expt. 49. To sublime Salammoniac and Camphor. Place in 

 a dry test-tube a few grains of salammoniac (chloride of ammonium) 

 and apply heat ; the solid substance will soon disappear from the 

 hot bottom of the test-tube, but nearer the mouth a ring of white 

 condensed solid matter will become visible ; this solid is sublimed 

 salammoniac. 



Eepeat this experiment, using a few grains of camphor ; very 

 similar results will be observed. When camphor is kept in half- 

 empty bottles it generally sublimes to some extent spontaneously 

 in the bottles, so that the upper part becomes covered over with 

 particles of sublimed camphor often well crystallised. It is a 

 curious fa^b, and one for which no clear explanation is known, 

 that the camphor which thus sublimes usually deposits chiefly on 

 the side of the bottle which faces the light, and comparatively 

 little on the other side. You can easily verify this by corking up 

 a little camphor in a bottle, and leaving it for some weeks on a 

 shelf, where as much light falls on the bottle as possible, the 

 camphor bottles in druggists' shops often show this peculiarity, 

 which is not due simply to one side of the bottle being cooler than 

 the other, as might perhaps be supposed. 



Expt. 50. To sublime Iodine. Kepeat the previous experiments 

 with a few fragments of iodine instead of salammoniac or camphor ; 

 you will notice that the hot part of the tube becomes filled 

 with a beautiful deep violet-tinted vapour, which cools in the 

 upper part of the tube to little black shining crystals. Iodine is 

 one of the comparatively few substances that form coloured vapours 



