SUBLIMATION. 59 



when heated, as well as belonging to the comparatively small class 

 of solids that sublime without previous fusion; its name is derived 

 from the former circumstance (1008775 = Greek for violet-coloured). 



Expt. 51. To sublime Carbonate of Ammonium. Repeat the 

 previous experiment with some solid carbonate of ammonium ; 

 sublimation will occur as before, and the upper part of the test- 

 tube will become covered with minute crystals. The vapour 

 given off in this experiment is alkaline, so that if a red litmus test- 

 paper be moistened and placed in the mouth of the tube it will be 

 turned blue (Expts. 142, 203). 



Carbonate of ammonium constitutes the basis of ordinary smelling 

 salts ; a drop or two of oil of bergamot, or some analogous sweet- 

 smelling essential oil, is added to the coarsely-powdered salt, so 

 that the vapours given off consist not only of ammonia, but also of 

 essential oil, thus modifying the odour. A little quicklime added 

 to the mixture makes the production of ammoniacal vapours much 

 more vigorous. 



Expt. 52. To separate different kinds of Solids by Sublima- 

 tion. Just as water may be separated from saline matters by 

 distillation (Expts. 36 and 37), so may volatile solids like salam- 

 moniac, camphor, and iodine be separated from non-volatile solid 

 matter by sublimation. 



Mix intimately together a little fine sand and salammoniac, 

 place the mixture in a test-tube, and apply heat ; a sublimate of 

 pure salammoniac will be obtained, whilst the sand will remain 

 unchanged at the bottom of the tube. 



Mix a little common salt (dry and in fine powder) with some 

 camphor, and heat the mixture gently in a watch-glass covered ovei 

 with a second one, the two being placed mouth to mouth, taking 

 care not to crack them by too strong a heat. By nd by the 

 camphor will have all sublimed into the upper glass to which it 

 will stick, whilst the salt will remain in the lower one. You car 

 prove that the lower glass contains salt by dissolving the contents 

 in distilled water (after cooling) and adding a little nitrate of 

 silver solution as a test (Expt. 37) ; if you shake up the sublimed 

 camphor with water, and test this fluid in the same way, you will 

 find that no salt is present therein, or at most only a trace due to 

 the mechanical carrying away of minute particles of salt by the 

 camphor-vapour whilst escaping, just as air might carry dust 

 with it. 



Expt. 53. Preparation of Crystals by Sublimation. Many 

 substances when sublimed deposit on the side of the subliming 

 vessel as crystals ; but generally the crystals are but small, and not 

 easily examined without a magnifying glass. Some few bodies, 



