CHEMICAL SCIENCE. 207 



of manganese," he adds, "is opalescent and crystalline; that of 

 chromium more fluid, and less variable at ordinary temperatures. 

 When the latter is heated in a small porcelain capsule in the air, 

 as the mercury flies ofl' in vapor it carries oft' mechanically with 

 it particles of chromium, which take fire, producing a singular 

 scintillation, which is best observed in a darkened room. At 

 length the chromium remaining in the capsule suddenly becomes 

 incandescent, and burns to oxide." — Mechanics'' Magazine. 



BUKNESTG OF A FRICTION MATCH. 



Among the varied operations of the arts there is perhaps no 

 other involving so many chemical and physical changes, and so 

 many philosophical principles, as the burning of a friction match. 



First in importance is the intense affinity of phosphorus for 

 oxygen, as it is this property which makes a friction match possi- 

 ble. This affinity is so strong that when pliosphorus is exposed 

 to contact with the oxygen of the atmosphere at ordinary tem- 

 peratures, the two substances combine slowly, generating light 

 which is visible as a faint glow in the dark ; and if the temperature 

 is raised to about 120°, the combination goes on with that rapidity 

 which we call combustion. It is easy to pi'oduce this degree of 

 tempei-ature of friction, — hence the possibility of the friction 

 match. 



It is necessary, indeed, to modify the inflammability of phos- 

 phorus for its use in a friction match, and this is done by mixing 

 it with a little gum. The gum also protects it from slow combus- 

 tion in the atmosphere. 



The flame of phosphorus, though intensely hot, will not set fire 

 to pine wood ; it is, therefore, necessary to interpose some sub- 

 stance more readily inflammable than wood : the substance usu- 

 ally employed js sulphur. Pine wood ignites at a temperature of 

 about 600°, and sulphur at 450° to 500°. The phosphorus, in 

 burning, kindles the sulphur, and the sulphur flame sets fire to 

 the wood. 



The refusal of the phosphorus flame to kindle Avood is fruitful 

 of suggestions. The quantity of heat generated by the burning 

 of any substance is in proportion to the quantity of oxygen with 

 which tlie substance combines. One atom of phospliorus, in 

 biu-ning, comltines with five atoms' of oxj-gen, producing phos- 

 phoric acid, P O5. The atom of phosphorus weighs 32, and the 

 atom of oxygen 8, so the proportion by weight is 32 pounds of 

 phosphorus to 40 of oxygen. Sulphur, in burning, combines with 

 oxygen in the proportion of one atom of sulphur to two of oxy- 

 gen, S O2, and, as the atomic weight of sulphur is 16, the propor- 

 tion by weight is 32 of sulphur to 32 of oxygen ; consequently 

 phosphorus should generate more heat in burning than sulphur. 



Again, this law is modified by either the oxygen or the com- 

 bustible undergoing a change of form in combining. If a sub- 

 stance is changed from the gaseous to the solid state, heat is 

 evolved ; if from the solid to the gaseous, heat is absorbed. Now, 

 phosphoric acid is a solid, while sulphurous acid is a gas. Phos- 



