SCIENTIFIC TERMS. 137 



Aerostation, the art of ballooning or navigating in the air. 



Affinity, an inclination which certain bodies have to combine chemi- 

 cally. See page 14. 



Agate, a species of transparent quartz. 



Air-gun, an instrument to propel bullets by means of the air. See 

 page 39. 



Air-pump, a pneumatic machine for exhausting the air. See page 38. 



Ajutage, a sort of tube used in water-works for jets d'eau. 



Albumen, one of the radical parts of animal substances. It exists in 

 its most perfect state in the white of eggs, and in the serum of the 

 blood ; it also abounds in milk, and to this it is chiefly indebted for 

 its nutritious qualities. 



Alcohol, highly rectified spirits of wine. It constitutes the basis of 

 all spirituous liquors, and in this country it is procured from wheat, 

 barley, molasses, &c. ; in the wine countries it is obtained from 

 wine, whence the term spirits of wine. Alcohol is used as a solvent 

 of resinous substances and essential oils ; it is also used in thermo- 

 meters for measuring extreme degrees of cold, as it will not freeze. 

 Tinctures of various substances are extracted by means of diluted 

 alcohol. 



Alembic, a vessel used in Chemistry for distillation. 



Alkalies, peculiar substances which have a caustic taste, and a strong 

 tendency to combine with acids, and thus form various salts. They 

 change the blue juices of vegetables to a green, and the yellow to a 

 brown. 



Alloy, a combination of two or more metals ; thus brass is an alloy of 

 copper and zinc. 



Alluvial, " Deposition," soil formed by the destruction of mountains 

 through the agency of water. 



Aluminum, the metallic base of Alumina or common clay. 



Alum, a well-known mineral salt, of an acid taste, generally prepared 

 artificially from Alum-slate, though sometimes it is produced natu- 

 rally. Alum is of very great use in the arts. By its means the 

 colours are fixed in dying ; in tanning it is used to restore the cohe- 

 sion of the skins which had been impaired by the action of the 

 lime ; bakers use it to whiten their bread ; vintners to fine down 

 their wines ; in the dairy it assists in the separation of the butter, 

 and fishermen often use it to dry their fish. In medicine as a 

 styptic and tonic it is particularly valuable. There is scarcely any 

 substance so generally useful and" so plentiful as Alum. 



Amalgam, a combination of mercury with another metal. 



Amethyst, a transparent gem of a purple colour. 



Ammonia, the volatile alkali. See page 74. 



Ammonite, a fossil shell of a spiral shape. It takes its name from 

 Jupiter Ammon. whose statues were represented with rams' horns. 

 It is from the smallest size to three feet in diameter. 



Amygdaloid, a compound mineral composed of spar, green earth, &c,, 

 imbedded in green stone, or in wacke. 



Analysis, the resolution of a substance into its component parts. 



Anemometer, an instrument for measuring the force of the wind. For 

 Meteorological instruments, see page 58. 



