ir>8 



-. Tin- SUOM nice- called ! !-<>. i-'nl' x'-' eyohe oxygen at a e;reater o 

 le>s heat (and also by the action of many acids). They usually contaii 

 nift;ils combined with a laruv quantity of oxygen. Peroxides arc tin 

 hiu'he-t oxides df certain metals ; those metals \vhidi form them irene 

 rally Lfive seyeral compounds with oxygen. Those of tin- lowe-t decree 

 of oxidation, containing the least amount of oxygen, are generally sub 

 stances which are capable of easily reacting on acids for instance 

 with sulphuric, acid. Such low oxides art 4 called bases. Peroxide: 

 contain more oxygen than the ba-es formed by the same metals. Fo 

 example, lead oxide contains 7'1 parts of oxygen in 1 < >< I parts, and i: 

 basic, but lead peroxide contains ]'.}'.} parts of oxygen in lou parts 

 ^^<t ii'/<i in x>< jn'i'n.i'n.Ji' is a similar substance, which is a solid of a darl- 

 colour, and occurs in nature. It is employed in the manufacture! 

 under the name of black oxide of manganese (in (lerman. ' Braunstein, 

 the pyrolusite of the mineralogist). Peroxides are able to eyolyt 

 oxygen at a more or less elevated temperature. They do not then pan 

 with all their oxygen, but with only a portion of it. and are c<>nyerte< 

 into a lower oxide or base. Thus, for example, lead peroxide, on heat- 

 in U\ u'ives oxygen and lead oxide. The decomposition of this peroxidt 

 proceeds Somewhat easily on heating, eyen in a glass vessel, but manga- 

 nese peroxide <nl\" exolyes oxygen at a strong red heat, and therefore 

 oxygen can only be obtained from it in iron, or other metallic, or clay 

 yessels. This used to be the method for obtaining oxygen. .Man^'anest! 

 peroxide only ]>arts with one-third of its oxygen (accordiiiiLj to the 

 equation .">.M n().,= M n :( ( ), + ().,), whilst t wo-tliirds remain in the solid 

 substance which forms the residue, from the heating. Metallic peroxides 

 are also capable of eyolvimj; oxygen on heating with sulpliuric acid. 

 'J'hey then e\'ol\e so much oxygen as is in excess of that necessary tor 

 the formation of the base, the latter reacting on the >ulplmric acid 

 forming a compound (salt) with it. Thus barium peroxide, when 

 heated with sulphuric acid, forms ox vgen and barium oxide, which gives 

 a compound with sulphuric acid which is termed barium sulphate 

 (BaO. J +H^SO I ^l>aS() 1 -f-H./)-r-O). This reaction usually proceeds 

 with irreater ease than the decomposition of peroxides by heat 

 a lone. Kor t lie purposes of experiment powdered man^am-M- peroxide is 

 usually taken and mixed with strong sulphuric acid in a lla.-d<. and the 

 apparatti- set up a- -ln>wn in Fig. L'S. r l'he gas \\-hicli is e\ol\ed is 



