REDUCTION TO AIR. 279 



of the experimental determinations de facto introduces 

 gross errors in practice. 



We will here only refer to the errors of 12 and 66 milli- 

 grammes " inadvertantly " committed by Stas in Nos. 8 and 

 6 of his famous syntheses of silver nitrate. See pp. 175-176. 



We may also recall the remarkable " rise " in Nos. 5 and 

 8 of the determinations of arsenic, though the reduction of 

 necessity involves a lowering of the ratio. See p. 230. 



By a most astonishing play of fate, in all these cases of 

 "inadvertency" the result was a "smoothening of the 

 curve," a most notable diminution of the deviations from a 

 constant mean, a truly wonderful diminution of residual 

 "errors." 



How strange that such inadvertent errors should reduce 

 the actual errors so as to reduce the final probable error of 

 the mean! 



We have strongly advised to leave the weighings without 

 reducing them to vacuum. 



We must insist on giving the actual weighings in air in all 

 cases, even if the weighings reduced to vacuum are given also. 



The former are the true results of observation ; the latter 

 \ve have seen to be often affected with very large errors, due 

 to errors of calculation or other causes. 



I shall here show how superfluous this entire reduction to 

 vacuum is, and how the exact comparison can be made by 

 the following most simple process of calculation. 



This process consists in calculating the change of our 

 absolute atomic ratio due to the buoyancy of the air. 



In other words, we prefer to reduce our absolute weights 

 to air, the very opposite of the common process. 



By the well known method, reduction to vacuum there is 

 a certain small factor k milligramme per gramme to be 

 added to the apparent weight or the weight in air. 



Consequently, the apparent weight will be obtained from 

 the absolute weight, by subtracting this small amount. 



These factors have been tabulated by Kohlrausch (Leit- 

 faden, IV Aufl., 1880, p. 286; also Ostwald, Hand und 

 Hilfsbuch, 1893; p. 47; also my General Chemistry, 1897, 

 pp. 220 and 231). 



