390 CHEMICAL DISCOVERY AND INVENTION 



University of Manchester. Dixon found that carbon monoxide 

 mixed with oxygen, when dried as perfectly as possible, by long 

 contact with phosphoric oxide, does not explode when an electric 

 spark is passed through the gas. The admission of a minute 

 trace of water vapour at once restores to the mixture its in- 

 flammability. This discovery has been very fruitful in the way 

 of discussion, and a hypothesis put forward soon afterwards to 

 the effect that chemical combination between two substances 

 was impossible without the presence of a small quantity of a 

 third substance met with a good deal of favour. This hypo- 

 thesis seemed to be further supported by discoveries of a similar 

 kind made a few years later by Dr. H. Brereton Baker, now 

 Professor in the Imperial College of Science and Technology at 

 South Kensington. Dr. Baker's experiments showed that carbon, 

 sulphur, and even phosphorus, when carefully dried, refuse to 

 burn in oxygen when heated above the temperature at which 

 they usually ignite. He also found that ammonia mixed with 

 hydrogen chloride, and nitric oxide with oxygen are indifferent 

 when the gases are well dried. Whether in all cases a third sub- 

 stance is essential to the act of chemical combination must, how- 

 ever, be still regarded as an open question, notwithstanding the 

 interesting suggestiveness of the experiments referred to. Much 

 has yet to be learnt as to the constitution of gases and the real 

 nature of chemical action, especially since the doctrine concern- 

 ing electrons and their functions has become generally accepted 

 (see pp. 118 and 212). 



Notwithstanding the greatly increased knowledge in our time 

 about the properties of inflammable gases and of the conditions 

 prevailing in coal pits, it is, unhappily, true that disastrous 

 explosions continue to occur, in which many lives are lost, as 

 they were before the invention of the safety lamp, in 1817, by 

 Sir Humphry Davy. This fact is, of course, no ground for 

 argument against the utility of the safety lamp. 



The explosions which occur are due either to abuse of the 

 lamp, to gross neglect of rules by miners, to blown-out shots, or 

 some other cause. Among the sources of danger not recognised 

 a few years ago is the accumulation of fine coal-dust in many 

 workings. 



Attention was first called to the subject by Mr. William 

 Galloway so long ago as 1876, and much discussion and experi- 

 mentation has been carried on since that time. The presence of 



