A potential source of dangerous concentrations of hydrogen cyanide exists in the plating room of the Machine Shop where open plating baths containing cyanide salts are maintained and where solid cyanide salts are stored. Also the use of hydrogen sulfide in certain steps of the waste disposal process has lead to noticeable and sometimes objectionable concentrations of this gas in the air of the "WD" Building. In view of the toxic properties of these two gases, it was desirable to set up suitable tests to determine the actual concentrations present in the air of the respective working areas.