338 SCIENTIFIC RECREATIONS. 



receive certain names. The following table will explain the terms used ; for 

 instance, we find that 



Compounds of Oxygen are termed Oxides, as oxide of copper. 



Hydrogen Hydrides, as hydride of potassium. 



Chlorine Chlorides, as chloride of sodium. 



Nitrogen Nitrides, as nitride of boron. 



j, Bromine Bromides, as bromide of potassium. 



Iodine Iodides, as iodide of potassium. 



Sulphur 



Selenium Selenides, as selenide of mercury. 



Carbon Carburets* J as carbide of nitr S en > and so on - 



The above examples refer to the union in single proportion of each, 

 and are called Binary Compounds. When more than one atom of each 

 element exists in different proportions we have different terms to express such 

 union. If one atom of oxygen be in the compound it is called a "monoxide,"" 

 or " protoxide " ; two atoms of oxygen in combination is termed " dioxide," 

 or "binoxide"; three, "trioxide," or " tritoxide " ; four is the " tetroxide," 

 or " per-oxide," etc. When more than one atom, but not two atoms is 

 involved, we speak of the sesgvi-oxide (one-and-a-half), " oxide " being: 

 interchangeable for " sulphide " or " chloride," according to the element. 



There are other distinctions adopted when metals form two series of 

 combinations, such as ous and ic, which apply, as will be seen, to acids, 

 SulphunV and sulphun?//.y acids, nitric and nitrous acid are familiar examples. 

 In these cases we shall find that in the acids ending in " ous " oxygen 

 is present in less quantity than in the acids ending in ic. The symbolic 

 form will prove this directly, the number of atoms of oxygen being written 



below, 



Sulphurous Acid = H 2 SO 3 . Nitrous Acid HNO-j. 



Sulphuric Acid = H 2 SO 4 . Nitric Acid = HNO 3 . 



Whenever a stronger compound of oxygen is discovered than that 

 denominated by ic, chemists adopt the plan of dubbing it the per (virep over) y 

 as per-chloric acid, which possesses four atoms of oxygen (HC1O 4 ), chloric 

 acid being HC1O 3 . The opposite Greek term, VTTO (htipo, below), is used for 

 an acid with less than two atoms of oxygen, and in books is written "hypo "- 

 chlorous (for instance). Care has been taken to distinguish between the 

 higher and lower; for "hyper" is used in English to denote excess, as- 

 hyper-critical ; and hypo might to a reader unacquainted with the derivation 

 convey just the opposite meaning to what is intended. 



While speaking of these terminations we may show how these distinctive 

 endings are carried out. We shall find, if we pursue the subject, that when 

 we have a salt of any acid ending in Ic the salt terminates in " ate" Simi- 

 larly the salts of acids ending in ous, end in " ite" To continue the same 

 example we have 



Sulphur<?//j Acid, which forms salts called 

 SulphurzV: Acid, Sulphates. 



Besides these are sulphides, which are results of the unions or com- 



