1 , 1 PRINCIPLES OK CHEMISTRY 



liu'ht. v. Inch \vas at one time proposed for illuminating lighthouses. 

 At present in the majority of cases electric light, osving to its constancy 

 and other advantages, has replaced it for this purpose. The light 

 produced bv lime in detonating gas is called the /JrHnimond fif/Jtf or 



The above cases form examples of the combustion of (dements in 

 oxvgen, but exactly similar phenomena are observed in the conJiuxtion 

 of itiii j:ini //'/\. So, for instance, the solid, colourless, shmv substance, 

 naphthalene. (',,,! F s , burns in air with a smoky (lame, whilst in oxygen 

 it continues to burn with a very brilliant llame. Alcohol, oil. and 

 other substances burn brilliantly in oxygen on conducting the oxygen 

 by a tube to the flame of lamps burning these substances. A high 

 temperature is thus evolved, which is sometimes taken advantage of 

 in chemical practice. 



I n order to understand why combustion in oxvgen proceeds more 

 rapidlv. and is accompanied by a more 1 intense heat etl'ect, than com- 

 bustion in air.it must be recollected that air is oxvgen diluted with 

 nitrogen, which does not support combustion, and therefore fewer par- 

 ticles of oxygen flow to the surface of a substance burning in air than 

 when burning in pure oxygen. The chief reason of the intensity of com- 

 bustion in oxygen is the high temperature acquired by the substance 

 burning in it. Let us consider as an example the combustion of sulphur 

 in air and in oxygen. If 1 gram of sulphur burns in air or oxvgen it 

 evolves in either case I'L'oO unitsof heat /.''., evolves sufficient heat for 

 heating i' _'"><> grams of water 1" ('. This heat is first of all transmitted 

 to th'- sulphurous anhydride, HO.,, formed by the combination of sulphur 

 with oxygen. In its combustion 1 gram of sulphur forms '2 grams 

 of sulphurous anhydride /'.'., the sulphur combines \\ith 1 gram of 

 o\vg ( 'H. In order that 1 gram of sulphur should have access to 1 gram 

 of oxvgen in air. it is necessary that .">! grams of nitrogen should 

 simultaneously reach the sulphur, because air contains seventy-seven 

 parts of nitrogen (by weight) per twenty-three parts of oxvgen. Thus 

 in the combustion of 1 gram of sulphur, the L'l'on units of heat are 

 t ransmitl od to '2 grains of sulphurous oxide and toat least ."> I grams of 

 nitrogen. As (Hr>f) units of heat are required to raise 1 gram of 

 sulphurous anhydride I ('., therefore L' grams require <).'}] units. So 

 also ."> 1 grains of nitrogen require " I '/ O'L'll or O-S."> unitsof heat, 

 and therefore in order to raise both gases 1 ( '. n-., I 4- n-s:l or I'll 

 units of heat are required, lint as the combustion of the sulphur 

 evohcs '-'.I'-"' 1 ' units of heat, therefore the gases miuht be heated (if 



their sjH-citic heats remained constant) to ~ or 1D71 < '. That 



