124 PRACTICAL LESSONS IN SCIENCE. 



two volumes of water vapor, containing 2,000 molecules or 6, 000 

 atoms. The two-atom molecules of hydrogen and oxygen were 

 rearranged into three-atom molecules of water vapor, diminish- 

 ing the bulk by one-third. With ammonia the case is similar, one 

 volume of nitrogen containing 1,000 molecules or 2,000 atoms, 

 unites with three volumes of hydrogen containing 3,000 mole- 

 cules or 6,000 atoms, forming two volumes of ammonia, con- 

 taining 2,000 molecules with 8,000 atoms. The two-atom 

 molecules were broken up and rearranged into four-atom mole- 

 cules and the volume diminished by one-half. Thus the atomic 

 theory, Avogadro's principle, the theory of valence and the 

 phenomena of combination by volume, all seem to harmonize 

 with the facts of definite and multiple proportions in chemical 

 combinations, and to sustain and mutually verify each other. 

 The law of definite proportions has been demonstrated, the 

 others are still theories. 



It has been found that elements at the instant they are set 

 free from compounds are much more active and can effect 

 changes which they cannot effect under other circumstances. 

 Hydrogen gas passed into nitric acid causes no change, but 

 hydrogen liberated in direct contact with nitric acid reduces the 

 acid and forms the lower oxides of nitrogen. Examples of simi- 

 lar action are of frequent occurrence. An element at the instant 

 of its liberation is said to be in the nascent state or atomic state 

 when it seems to be more active than after the atoms have com- 

 bined into molecules. 



BROMINE (Br) is a dark brown liquid heavier than water having 

 an irritating disagreeable odor, hence the name, meaning a stench. 

 It is the only non-metal which is a liquid at ordinary tempera- 

 tures. It occurs in seawater and other natural brines, as 

 magnesium bromide, which is the main source of the bromine of 

 commerce. It is generally obtained from bittern, the residue 

 which remains after sodium chloride has been crystallized out 

 from the natural brines. Bromine forms compounds with hydro- 

 gen and oxygen, which are analogous to those of chlorine, and in 

 physical and chemical properties is somewhat similar to that 



