small degree, are termed t ndijj'' r< it' <>,i-'i<l<-s. Such a re the peroxides, of 

 Nvhich mention li;is before brcli made. 



1 he class (it oxides capable of entering into mutual combination 

 we Nvill term sit/ hi'' <>.<></>, >. Thev t'all into two chief i^roups at least, 

 a- regards t he mo-t extreme members. Tin- members of one group do not 

 combine with each other, l>ut combine with the members of the other 

 u;roup. As representative <f one group niav lie taken the oxides of 

 the metals, magnesium, sodium, calcium. iVc. Representatives of the 

 othi-r uToup are the oxides formed by the non-metals, sulphur, phos- 

 phorus, earbon. If we take, for instance, the oxide of calcium or 

 lime, and bring it into contact with oxides of the second ^roup, there 

 ensues very readv combination. r J"lius. for instance, if \\-e mix calcium 

 oxid'- \\~ith oxide of phosphorus, thev combine \\ith i^reat tacilitv. with 

 the evolution of much heat. If we pass the vapour of sulphuric an- 

 hvdride. obtained by the combination of sulphurous oxide with oxv^en, 

 over pieces of lime heated to redness, then the sulphuric anhydride is 

 absorbed by the lime, with the formation of a substance called 

 calcium sulphate. I he oxides of the first kind, which contain 

 metals, are termed imxir a. r, <!,.-< iii' Imws. Lime is a familiar example 

 of this class. The oxides of the second group, which are capable of 

 combining with the bases, are termed a ithi/<lri< ' x <>f /// <iri</s or <n'n1 

 a. i-iil, N. Sulphuric anhydride, S( ). , may l>e taken as a type of the 

 v;roup. It is foi'iued by the combination of sulphur with oxygen : by 

 the addition ot a fresh (juantitv of oxx'gen to the above-mentioned 

 sulphurous anhvdride, S( ).,. b\ - passing it and oxvgen o\'er incandescent 

 sponu;v platinum. ( 'arbonic anliydride loften termed "carbonic acid,' 

 (.'O.,). [ihosphoric anliydride, sulphurous anhydride, are all acid oxides, 

 fur thev can combine \\iih such oxides as lime or calcium oxide, 

 magnesia or magnesium oxide, .MgO, soda or sodium oxide. Na.,<), 

 iV ' ' . 



It a i;]\eii element form one basic oxide, it is termed the n.i-i<li : for 

 example, calcium oxide, magnesium OXlile. potassium oxide. Some 

 indill'ereiit oxid-s ai'e also called 'oxides ' it' i he\ ha \ e not t lie projiert ies 

 of peroxides. ;ind ai 1 he same time do not si IONS' the properties of acid 

 anh vd rides tor mst a nee. carbonic oxide, ot which men t ion has already 

 been made. If an clou'-lit forms t NS'o basic oxides (or t NS o indlHerent 

 oxide- not haxin^ the characteristics of a peroxide) then that of the 

 lower degree of ox ida t ion i- ca lied a stilio.i'i<li that is. su box ides contain 

 Ies- ox Vgen than oxides. 'Mills. \s hen copper Is hea t ed to 1'ei I ness 111 a 

 furnai-e it increases in \vei^ht and absorbs oxvifen, until for '"> pails 

 of copper thel'e is absorbed not more than > pa rt - of ox \gen b\- NS'eigllt, 

 tormiiiL;' a red muss. NS'hich is suboxide ot copper : but if the roasting 



