278 LECTUEES TO SCIENCE TEACHERS. 



accuracy with which he conducted his experiments it may 

 be mentioned that he determined the expansion of air 

 in the retort when nothing else was present. He first 

 warmed it, and generally found the water was displaced ; 

 then heating it to a low red-heat he measured the amount 

 of expansion which took place under those conditions, 

 and found it due to the difference in volume. On heat- 

 ing it to a bright white heat the volume increased to 

 three times. He then placed in his retort various sub- 

 stances, almost anything he could lay his hands on, 

 organic or inorganic, and submitted them to what we 

 should now call destructive distillation. The gases pro- 

 duced filled this bolthead more or less, and he noticed 

 the volume at the end of the heating and after it had 

 cooled, and then after allowing it to stand over water 

 for some days. We know at the present time that when 

 organic bodies are heated, one of the products is carbonic 

 anhydride, which is soluble in water; and consequently 

 in Hales' experiments the gas was continually disappearing, 

 or, as he described it, it lost its elasticity ; but still, as he 

 thought he was dealing with common air, he never imagined 

 he had anything but common air in these old experiments. 

 He imagined that the gas had again become solid, or else 

 that it was re absorbed by the body left in the retort. 

 However, he was a man of considerable intelligence, a 

 philosophic clergyman. He was rector of Faringdon in 

 Hampshire, and the minister of Teddington in Middlesex. 

 He says at the end of his paper : " If those who un- 

 happily spent their time and substance in search after an 

 imaginary production that was to reduce all things to 

 gold, had instead of that fruitless pursuit bestowed their 

 labour in searching after this much-neglected volatile 

 Hermes, which has so often escaped through their burst 

 receivers in the disguise of a subtle spirit, as mere flatu- 

 lent explosive matter, they would then, instead of reaping 

 vanity, have found their researches rewarded with very 

 considerable and useful discoveries." This is so absolutely 

 true that I can scarcely refrain from bringing it before 

 you, although it is 150 years old. 



The measurement of the goodness of the air seems to 

 have been first attempted by Fontaiia about 1770, and 

 afterwards by Priestley in 1774, and about the same time 



