CHEMISTRY OF THE EIGHTEENTH CENTURY. 353 



isted, that it combined with matter and passed from its combination 

 with one body to join another, that caloric (heat} is the result of its 

 combination with inflammable air, etc. Bergmann had charged Scheele 

 to investigate the composition of air, and in his researches on this sub- 

 ject, when he is dealing with facts, Scheele shows himself admirably 

 qualified for the task. The arrangement by which he determined the 

 proportion of " dephlogisticated air" (oxygen) 

 contained in the atmosphere is shown in Fig. 

 172. A bell jar containing air is inverted in 

 the vessel A over water. A tall stand within 

 B supports a small cup c, in which is placed a 

 mixture of iron-filings and sulphur moistened 

 with water. The capacity of the vessel B was 

 determined, and marked on a scale E on the 

 side of the bell jar for various levels of the 

 water within, allowance being made for the 

 space occupied by the stand. After some 

 time the oxygen of the air is completely ab- 

 sorbed. Bergmann thus estimated that -^-rds FIG. 172. 

 of atmosphere consisted of oxygen. 



In mineral chemistry Scheele is distinguished by his study of a 

 substance which was then called magnesia nigra, i.e., black magnesia. 

 This is no other than the substance we now call black oxide of man- 

 ganese. He found, on heating this substance with sulphuric acid, a 

 pinkish-white salt (sulphate of manganese) was the product. He found 

 also that during the solution of the black oxide of manganese in the 

 acid, gas was evolved, which was no other than oxygen. In trying the 

 action of the several acids on the black oxide he came to hydrochloric 

 acid, or, as it was then called, "muriatic acid;" and the gaseous body 

 evolved when these substances are heated together could not be over- 

 looked. But let us hear his own account of the matter : " I poured," 

 he says, *' an ounce of muriatic acid on half an ounce of powdered 

 black magnesia. This mixture, left to itself in the cold, became yellow 

 coloured, and on warming it a strong smell of aqua-regia was percep- 

 tible. In order to study this phenomenon, I proceeded in this way : I 

 fastened an empty bladder on the end of the tube of the retort, which 

 contained the mixture of black magnesia and muriatic acid. As the 

 effervescence of the liquid proceeded the bladder swelled up; and 

 when it was filled I removed it, and found that the gaseous substance 

 it contained had coloured it yellow, just as aqua-regia would have 

 done. The gas was not fixed air (carbonic acid gas) ; its smell was 

 extremely powerful and penetrating, and it particularly affected the 

 nostrils and the lungs. In fact, one would have taken it for the 

 vapour of aqua-regia." Scheele afterwards collected this gas in bottles 

 according to Hales' method (p. 342), and gave a description of the 

 properties of the new substance. It corrodes the corks, turning 



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