History of Air-Analysis 15 



sulphate saturated with nitric oxide would absorb 5 to 6 c.c. of oxygen. 

 Comparative tests were made with phosphorus and alkaline sulphides. 



In his analyses of atmospheric air with a saturated solution of nitric 

 oxide, he never found a change in the constituents. The air on October 

 3, 1800, on the sea, at the mouth of the Severn, with a strong west wind 

 blowing over the Atlantic Ocean, contained 21 per cent of oxygen. Ex- 

 actly the same amount was found in air brought from the coast of Guinea 

 to Dr. Beddoes by two Liverpool surgeons. Davy's ingenious use of the 

 ferrous-sulphate solution of nitric oxide was short-lived, for he himself 

 found that the alkaline sulphides always gave a somewhat larger absorp- 

 tion. 



Allen and Pepys 1 employed the ferrous sulphate-nitric oxide method 

 to analyze not only air, but some gaseous mixtures rich in oxygen. They 

 report that outdoor air was continuously found to contain 21 per cent of 

 oxygen. 



The last writer to make any considerable use of the nitric-oxide eudiom- 

 eter was Dalton, 2 who, comparing the Volta hydrogen eudiometer with 

 the nitric-oxide eudiometer and the sulphide of lime absorption method, 

 says: 



The nitrous gas eudiometer is of singular utility on many occasions. No other can 

 exceed it in accuracy when mixtures contain very little, as one or two per cent of oxygen; 

 or on the other hand when nearly the whole of the gas is oxygen. But when the mixture 

 of gases contains from twenty to eighty per cent of oxygen, as in the case of common air, 

 it is not the best when great exactness is required. 



THE BEGINNINGS OF ACCURATE AIR-ANALYSIS. 



The early historical interest attaching to the development and exten- 

 sive use of the nitric-oxide eudiometer justifies the special treatment 

 which has been given of this method; nevertheless other absorbents for 

 oxygen were used. The large number of scientists experimenting daily 

 with the newly discovered gas, oxygen, and acquiring information with 

 regard to its properties, rapidly brought together a series of methods for 

 determining this gas in air. While the nitric-oxide method has long been 

 discarded as utterly worthless, the alkaline sulphides first employed by 

 Scheele were for some time used in air-analyses, and phosphorus for absorb- 

 ing oxygen, likewise employed by Scheele, has even to-day an extensive 

 use. The explosion of air with hydrogen, first employed by Volta, has also 

 withstood the critical attacks of over 100 years and to-day is much used. 



As Scheele found from his experiments with different absorptive agents 

 variations in the oxygen content of air, so Lavoisier likewise, using various 

 agents, was unable to find any satisfactory value for the percentage of 



oxygen, for we find in his reports varying values assigned to the oxygen 







1 Pepys, Philosophical Transactions, 1807, Part I, p. 247; Allen and Pepys, Philo- 

 sophical Transactions, 1808, 8, p. 255. 



2 Dalton, Philosophical Magazine, 1838, 3d ser., 12, p. 158. 



