Dr. Thomas Andrews : The Great Chemist 121 



from the electrolysis of water contained hydrogen. Other scientists 

 believed it to be composed wholly of oxygen. It was soon shown, 

 however, that pure and dry oxygen could be partially converted 

 into ozone by passing through it an electric spark. 



It was also noticed that in the formation of ozone in oxygen 

 the volume was reduced, and it was argued that ozone was an 

 altered or allotropic form of oxygen, having a density greater than 

 the parent gas. Andrews' experiments were undertaken to settle 

 this question and he succeeded in proving that, no matter in what 

 way Ozone was prepared, it was always the same body, with the 

 same properties, and that that obtained from the electrolysis of 

 water did not contain Hydrogen as had been supposed. It was 

 found that Oxygen could only be partially changed into Ozone by 

 the action of the spark, but it was also discovered that certain 

 reagents seemed to absorb the Ozone when the combination took 

 place, and that by continuing the process and absorbing the Ozone 

 as formed, the whole of the Oxygen could thus be ultimately 

 transformed. It was soon apparent that the amount of Ozone 

 destroyed, as was supposed, by the chemical reagent used, and 

 accounted for by its increase in weight corresponded approximately 

 to the reduction in volume of the oxygen when the spark was 

 passed through it. It was then necessary to investigate the 

 matter further and discover the density of the allotropic modi- 

 fication of oxygen which he had proved to be formed. In 1857 

 the first account of the experiments undertaken in conjunction 

 with P. G. Tait, then Professor of Mathematics in Belfast and a 

 member of our society^ appeared, and was followed by publication 

 of a further series in 1859 and 1860. 



Never was Andrews' unrivalled accuracy in experiment better 

 shown than in this series, which ran up against a stone wall by 

 suggesting an infinite density for Ozone. It is true that the two 

 experimenters saw another solution to the difficulty, which was 

 really the true solution, but which was named only to be rejected 

 as too improbable. Soret later proved that the density of Ozone 

 was one and a half times that of Oxygen, and that the solution 

 rejected by Andrews and Tait was the true one. 



