28 CHEMISTRY. 



Gasom'etry. — The science, art, or practice of mrasuring gnsm. 

 It teaches, also, the nature and properties of these elastic 

 fluids. 



Hy'drates. — Compounds containini^ water as one of their 

 proximate elements, and in definite proportion. 



Hydrom'eter (Or. hnddr, water, and mefron, measure). — An 

 instrument for determining the specific gravity of liquid.s. 



Hydrom'etry (Ur. hudOr, water, and metroa^ measure). — The 

 art of determining the specific gravity of liquids. 



Incompat'ibles. — Substances 'h'liich cannot be united in solu- 

 tion without decomposition or chemical change. 



Isom'erism. — An identity of elements and of atomic propor- 

 tions, with a difference in the amount combined in the 

 compound molecule, and of its essential qualities ; as in 

 the case of the physically unlike compounds of carbon and 

 hydrogen, consisting one of 1 part each, another of 2 parts 

 each, and a third of 4 parts each. 



Met'alepsy (Gr. metaltpsis, participation). — Change or varia- 

 tion in a series of compounds under a type, by substitutions 

 of different elements or substances for an ecjuivalent in the 

 type, as when a substance contains hydrogen, and, when 

 subjected to change, takes up an equivalent for each atom 

 of hydrogen it loses ; called also theory of substitutions. 



Met'alloids. — A name sometimes applied to the metallic bases 

 of the alkalies and earths. 



Oxida'tion. — The process of converting metals or other sub- 

 stances into oxides, by combining with them a certain por- 

 tion of oxygen. 



Radical. — An element (or molecular group, and thence called 

 compound radical), whether insoluble or not, which may be 

 transferred from one combination to another in exchange 

 for one or more atoms of hydrogen or its representatives. 



Rectifica'tion. — The process of refining or purifying any sub- 

 stance by repeated distillation, which separates the grosser 

 parts. 



Saccharom'eter (L. sacchamm, sugar, Gr. metron, measure). 

 — A hydrometer for determining the density of syrups. 



Specific Gravity. — The weight of a body compared with 

 another of the same bulk taken as a standard. Water is 

 the standard for solids and liquids, common air for gases. 

 Thus, the exact weight of a cubic inch of gold, compared with 

 that of a cubic inch of water, is called its specific gravity. 



