50 Chemistry. [Lecture 25. 



gas, on the contrary, will not of itself support 

 combustion, because the presence of oxygen ga 

 is absolutely necessary to this effect, which is in 

 this case the result of the union of these two 

 gasses. 



Hydrogen combines with the other simple 

 combustibles, forming sulphuretted hydrogen 

 gas, phosphuretted hydrogen gas, carburetted 

 hydrogen gas, &c. 



The latter gas, obtained by the combustion 

 of coal, is that which is employed for the pur- 

 poses of illumination. It is this species of gas 

 which forms thejire-damp or blower, so destruc- 

 tive by its explosion, on the contact with flame 

 in coal mines. Against this evil, Sir H. Davy 

 has opposed an excellent contrivance, the safety- 

 lamp, in which the flame of the 'lamp, being 

 surrounded with wire gauze, the communication 

 of flame to the external explosive gas is prevented 

 by the cooling power of the metallic tissue. 



Hydrogen gas is not so pernicious when re- 

 spired as some other of the gasses. If much 

 diluted with common air, indeed, it may be 

 breathed without injury. 



V. PHOSPHORUS is one of those simply acidi- 

 fiable and inflammable substances which we find 

 in a solid form, though I do not know that it is 

 any where found native ; all that is used in philo- 

 sophy and commerce being obtained by an arti- 

 ficial process. As in the state of an acid it 

 forms one of the constituent parts of bones. 



