184 FRAGMENTS OF SCIENCE. 



but it so squeezes the more condensable vapours, and 

 acts with such condensing power upon the oxygen of 

 the air, as to bring both within the combining distance, 

 thus enabling the oxygen to attack and destroy the 

 vapours in the pores of the charcoal. In this way, 

 effluvia of all kinds may be virtually burnt up ; and 

 this is the principle of the excellent charcoal respirators 

 invented by Dr. Stenhouse. Armed with one of these, 

 you may go into the foulest-smelling places without 

 having your nose offended. 



But, while powerful to arrest vapours, the charcoal 

 respirator is ineffectual as regards smoke. The smoke- 

 particles get freely through the respirator. With a num- 

 ber of such respirators, tested in a proper room, from 

 half a minute to a minute was the limit of endurance. 

 This might be exceeded by Faraday's simple method of 

 emptying the lungs completely, and then rilling them 

 before going into a smoky atmosphere. In fact, each 

 solid smoke particle is itself a bit of charcoal, and 

 carries on it, and in it, its little load of irritating 

 vapour. It is this, far more than the particles of 

 carbon themselves, that produces the irritation. Hence 

 two causes of offence are to be removed : the carbon 

 particles which convey the irritant by adhesion and 

 condensation, and the free vapour which accompanies 

 the particles. The cotton-wool moistened with gly- 

 cerine I knew would arrest the first ; fragments of 

 charcoal I hoped would stop the second. In the first 

 fireman's respirator, Mr. Carrick's arrangement of two 

 valves, the one for inhalation, the other for exhalation, 

 was preserved. But the portion of the respirator which 

 holds the filtering and absorbent substances, was pro- 

 longed to a depth of four or five inches (see fig. 5). Under 

 the partition of wire-gauze q r at the bottom of the space 

 which fronts the mouth was placed a layer of cotton- 



