Let the liquid to be examined be introduced into a Döbereiner’s lamp [Fig. 10], or an apparatus constructed with a bottle and a funnel upon the same principle [Fig. 11]; and dilute the liquid with distilled water, until the lower cavity of the apparatus be nearly full, leaving space however for the tube of the funnel, a fragment of zinc, and some sulphuric acid. Put in a cylinder or rod of zinc, _a_; and then add sulphuric acid until a moderate effervescence ensue. Close the junction of the two vessels, and then, allowing a little gas to escape at _c_, shut the stop-cock, and let the gas fill the vessel A, by driving the liquid up into B. Having meanwhile fitted by a cork to the exit-tube, _c_, the glass tube, _d e_, which is loosely stuffed with raw cotton at the end _d g_, and has a bent plate of copper or tinned iron hung over it at _f_,—open the stop-cock, allow a little gas to escape so as to expel the air in _d e_, and then kindle the gas at _e_, which must be contracted to a capillary opening. Keep the flame low, and hold the surface of a white porcelain vessel across the middle of it for a few seconds. If no stain be produced on the porcelain, there is no arsenic in the fluid. If a stain be formed, regulate the escape of gas by the stop-cock so that the fluid may not rise above the middle of the lower vessel of the apparatus, and apply the heat of a spirit-lamp flame to the tube _d e_ on the left hand of the plate _f_, the purpose of which is to prevent the heat being communicated beyond that point. By and by, if there be arsenic in the fluid, a brilliant metallic ring will appear beyond _f_, owing to decomposition of arseniuretted-hydrogen gas. As soon as the crust is thick enough to present its properties characteristically, withdraw the spirit-lamp; place the tube _e h_ so that the flame at _e_ shall be completely within the ball, _i_; let the tube incline very slightly in the direction from _k_ to _l_; and allow a stream of cold water to trickle down upon the portion _k l_, which should be wrapped in a single layer of calico. Oxide of arsenic will gradually condense, partly in white powder or minute sparkling crystals in the ball and between _i_ and _k_, and partly between _k_ and _l_ in the form of a solution, which collects at the bend _l_. The solution which may be increased in quantity by boiling a little distilled water upon the powder in the ball and bend _i k_, is then to be subjected in small portions to the three liquid reagents, ammoniacal nitrate of silver, ammoniacal sulphate of copper, and hydrosulphuric acid.