Large bulk matter search for fractional charge particles

We have carried out the largest search for stable particles with fractional electric charge, based on an oil drop method that incorporates a horizontal electric field and upward air flow. No evidence for such particles was found, giving a 95% confidence level upper limit of $1.17\times {10}^{-22}$ particles per nucleon on the abundance of fractional charge particles in silicone oil for $0.18e<~|Q_{\mathrm{residual}}|<~0.82e.$ Since this is the first use of this new method we describe the advantages and limitations of the method.