The density of air was directly measured using a Pt-Ir kilogram prototype and a stainless steel kilogram as buoyancy artifacts (BA) in a balance using an automatic weight exchanger capable of handling four weights. The mass values of two other stainless steel weights as test objects placed on the same weight exchanger were determined by comparing them with the prototype of kilogram and using the air density measured in situ. The in situ BA method produced less uncertainty in obtaining the mass values of test weights than that by the BIPM equation method. The accuracy of the in situ direct determination of the air density could be improved by utilizing a stainless steel BA whose true mass and volume could have been known more accurately. BA then could measure the mass of any object with less uncertainty in situ.