DISCOVERY BY EXAMINING THE EFFECTS OF CONTACT. 557 



iestroyed colours, and tinged the bladder yellow as nitric 

 icid does.' ' Scheele's mode of collecting chlorine gas in 

 a bladder did not enable him to determine its characters 

 with so much precision as was afterwards done. But his 

 accuracy was so great that everything which he stated 

 respecting it was correct so far as it went.' l It was by 

 examining the action of hydrogen and oxygen upon each 

 other, under different circumstances, that the formation 

 of water by synthesis was first discovered. 2 Smithson 

 Tennant was the first to demonstrate, in the year 1791, 

 the existence of a phosphide of calcium, by heating to- 

 gether lime and phosphorus. 3 



The discovery of hydrogen acids was similarly effected. 

 After the time of Lavoisier, it was found that his general 

 statement or theory, that all acids contain oxygen, was 

 not correct. By means of an experiment, made before 

 several eminent scientific men in Edinburgh, Davy, in the 

 year 1812, showed that when dry ammonia was allowed to 

 unite with dry ' muriatic acid ' gas, little or no water was 

 produced, and therefore no oxygen was present. 



h. By examining the influence of time upon phe- 

 nomena. Time and space are the most fundamental 

 conditions of all things. The influence of time upon phe- 

 nomena is often neglected; and our knowledge of the 

 effect of this condition is the most imperfect of all, 

 largely because of the very limited duration of human 

 life. By subjecting substances to long-continued pro- 

 cesses, a multitude of new truths would probably be found 

 of which we are at present quite unaware. The forma- 

 tion of crystals, gems, precious stones, diamonds, &c., in 

 the earth is probably due to actions continued over long 

 periods of time. The discoveries by Andrew Crosse, of 



1 Thomson, History of Chemistry, vol. ii. p. 66. 



See pages 540, 541. 8 See page 518. 



