228 EIGHTEENTH CENTURY. FT. in. 



made up the weight which the limestone had lost. He then 

 reversed the experiment, and taking some water which had 

 lime dissolved in it, he passed some 'fixed air' into it, and, 

 as he expected, the gas joined itself to the lime and formed 

 a powdered white chalk at the bottom of the bottle. By 

 these two experiments he proved that limestone is composed 

 of lime and ' fixed air.' 



He then proceeded to examine the gas itself. He found 

 that animals died in it, and that a flame would not burn in 

 it, and also that it was the same gas as that which bubbles 

 out of beer and other liquids when they ferment, and often 

 out of mineral springs. He also proved that there is ' fixed 

 air ' in our breath, by breathing into a glass of lime-water, 

 and thus forming powdered chalk, which fell to the bottom 

 of the glass. 



All this Black discovered about ' carbonic acid,' which is 

 sometimes called * fixed air ; even now, when people speak 

 of it in effervescing drinks. He did not know that it is an 

 acid ; this discovery was made by Bergmann of Sweden, oi 

 whom we must now speak. 



Bergmann shows that Fixed Air is an Acid Works 

 out * Chemical Affinity' of many Substances. Torbern 

 Bergmann, who was born in 1735 * n West Gothland, was 

 the son of a tax-collector, and he had the greatest difficulty 

 in getting permission to study science. His father had in- 

 tended him for the law or the church, and it was not until 

 his scientific books had been burnt, and he had fallen ill 

 with disappointment, that they saw it was useless to oppose 

 him, and he was allowed to take his own course. From 

 that time he was happy ; he put himself under the great 

 Linnaeus, and in 1761 became Professor of Natural Philo- 

 sophy at Upsala, and afterwards of Chemistry at Stockholm. 



