History of Air-Analysis 17 



fe>entes saisons, dans differentes circonstances. On pourrait faire marcher ensemble 

 des experiences correspondates par la combustion du phosphore. J'ai toujours eu le 

 projet de me livrer a ces recherches, auxquelles j'6tais naturellement conduit par les ex- 

 periences que j'ai faites sur la salubrity de l'air des salles de spectacle et des dortoires des 

 hopitaux; mais je n'ai pu encore realiser mon projet. 



While Scheele first attempted a study of the effect of season and 

 weather conditions on the oxygen content, we find Lavoisier empha- 

 sizing the importance of recognizing the influence of geographical locality 

 upon the composition of the atmosphere. 



Alkaline sulphides were used by Guyton 1 to absorb the oxygen quan- 

 titatively from the air; calcium sulphide was likewise employed by de 

 Marti 2 in his analyses of the air of Catalonia. Upon comparing the dif- 

 ferent methods nitric oxide, the Volta hydrogen eudiometer, phosphorus, 

 moist iron and sulphur, and the alkaline sulphides de Marti decided 

 the last was the most satisfactory. The experiments were made during 

 1787, and his results are of especial interest, as they show his remarkable 

 intuitiveness. 



Among other refinements, de Marti recognized the importance of sat- 

 urating his absorbing solution with nitrogen before use. He says regard- 

 ing his researches: 



The proof by sulphuret is that best calculated to ascertain the quantity of vital air 

 contained in any gaseous fluid, since it will leave the mephitic air, and the other kinds of 

 air which do not combine with it, without fear of any other gaseous substance being pro- 

 duced, or any lost, except the quantity of vital air, which alone has an affinity with the sul- 

 phuret, as I assured myself in 1787. A hundred parts of atmospheric air exposed to sul- 

 phuret lost between 0.21 and 0.23; and as several other proofs on the same air, made with 

 nitrous gas, had taught me that it experienced no sensible variation, I was then convinced 

 that the air which we breathe in Catalonia is constantly composed of from 0.21 to 0.23 of 

 vital air, and from 0.77 to 0.79 of azotic gas. To ascertain whether there might not be 

 variations afterwards in the proportion of these two principles which constitute in the 

 atmosphere that elastic substance on which our life chiefly depends, I continued my 

 experiments by means of sulphuret. 



I repeated them so many times with atmospheric air, and on so great a number of 

 days, that the uniformity in my results demonstrates not only the exactness of this 

 method, but it seems to result from my observations made on the southern coast of 

 this province: 



1st, That the wind never caused the variation of a hundredth part in the respective 

 quantities of vital air and azotic gas which compose the elastic fluid of our atmosphere, 

 since I have always found that a hundred parts contained 79 of the latter and 21 of the 

 former, without ever reaching 22. 



2nd, That neither the moisture nor dryness of the atmosphere, nor the state of the 

 latter in being more or less charged with exhalations, nor serene nor rainy weather, oc- 

 casioned any difference. 



3d, That the proportion of the quantities of the two same principles was equally 

 constant during the days that Reaumur's thermometer stood at the freezing point, as 

 well as during those when it indicated 24 degrees of heat. 



1 Guyton, Chemisches Annalen, 1788, 1, p. 316; ibid, 1796, 1, p. 22. 



2 de Marti, Journal de Physique, 1801, 52, p. 173; also printed in Philosophical Maga- 

 zine, 1801, 9, p. 250. 



