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meafure, as is exprefied in the plate 

 by BB in Fig. 1. Then I obferve 

 with what number of the fcale the 

 firft divifion of the glafs tube above 

 the column of water coincides, 

 which fhews me at once how many 

 fub-divifions are remaining from 

 the two meafures of airs, or from 

 the 200 fubdivifions let up in the 

 tube, and thus indicates the degree 

 of goodnefs of common air, or in- 

 deed of any air approaching in 

 goodnefs to common air, or being 

 of an inferior quality. But this 

 method will not do in examining 

 dephlogifticated air, as this air re- 

 quires more nitrous air to bring it 

 to a full faturation. By this fimple 

 and eafy method the whole opera- 

 tion is performed in three or four 

 minutes ; and its accuracy is fuch, 

 that frequently in ten trials, made 



with 



