Abstract: The polarographic behavior of tri-valent arsenic in HCl solution has been studied. AS⁺⁺⁺ in 1—3 M HCl solution, without the addition of gelatiu solution, showed two well-defined waves. The first wave was more suitable for quantitative analysis, the diffusion current being proportional to the coacentration of arsenic within the range 10^-6-2×10^-3M. A mere trace of gelatin disturbed the wave from and caused the half-wave potential to shift to a more negative value. When the concentration of gelatin exceeded 0.02%, the two polarographic waves merged into a very spread-out wave, rendering the halt-wave potential and diffusion current unmeasurable.