CH. xxvil. CHEMICAL AFFINITY. 227 



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. This he showed 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, of 

 whom we must now speak. 



Bergmann shows that Fixed Air is an Acid Works 

 out the ' Chemical Affinity ' of many substances. Tor- 

 bern Bergmann, who was born in 1735 in West Gothland, 

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

 culty in getting permission to study science. His parents had 

 intended 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. 

 Bergmann made a great advance in chemistry by working 

 out the ' chemical affinity ' of many substances, and showing 

 how to make use of it to test or try mineral waters. 



Nearly a hundred years before Bergmann began to study 

 chemistry, Newton, when writing on attraction, had pointed 

 out that when substances are mixed together some kinds 

 attract each other very strongly and join together, making 

 one compound substance. For instance, he said, if you 

 put copper into nitric acid the copper will dissolve and dis- 

 appear ; but if you plunge a piece of iron into the liquid the 

 17 



