OF ARTS AND SCIENCES. 55 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



A SIMPLE METHOD OF CORRECTING THE WEIGHT 

 OF A BODY FOR THE BUOYANCY OF THE ATMOS- 

 PHERE WHEN THE VOLUME IS UNKNOWN. 



By Josiah Parsons Cooke. 



Presented May 9th, 1883. 



It is a familiar fact, that, in the usual method of accurate weighing, the 

 buoyancy of the atmosphere produces a sensible effect, whenever the 

 volume of the load differs materially from that of the equipoise. But, 

 as in all the ordinary processes of chemical analysis, the analyst deals 

 solely with relative weights, the presence of a perfectly dry atmosphere 

 does not influence his results, unless the conditions of temperature and 

 pressure have changed between the successive weighings ; and even 

 then the effect is insignificant in most cases. Still, when the volume 

 of the vessel weighed is considerable, differing from that of the weights 

 by as little even as twenty-five cubic centimeters (for example, in 

 weighing the absorption tubes used in "organic analysis "), the error 

 caused by variations in the density of the atmosphere may be sufficient 

 seriously to impair the accuracy of the result. 



In weighing large vessels — as in determining the density of a gas 

 — the effect of any variation of buoyancy is eliminated by the well- 

 known methods of calculating the results ; but the formulas usually 

 given for that purpose involve as known quantities the volume of the 

 vessel, the volume of the weights, the density of the air under the 

 standard conditions, as well as the temperature and pressure at the time 

 of the several observations ; and, since the calculations are somewhat 

 complex, and the required data not always readily obtained, the for- 

 mulas are seldom applied unless the volume of the load is quite large. 

 Moreover, in these formulas the effect of each factor cannot readily 



