The decomposition of zinc dust is accompanied by a lively evolution of gas; it is therefore necessary to continue the digestion of the sample till no more hydrogen is given off. Zinc dust contains both metals and their oxides, and methods which, from the volume of hydrogen generated, determine indirectly the percentage of metallic zinc do not give the real composition of the zinc dust. For the determination of the metallic components the material is digested with a solution of copper sulphate, which dissolves zinc and cadmium; the liquid is filtered, acidified, and decomposed with hydrogen sulphide, or treated with a solution of ammonium carbonate. The use of cupric chloride is not advisable, as it corrodes lead, and gives rise to the formation of soluble chloride of lead, which complicates the separation of zinc from cadmium. The best mode of operation is the following: Both copper sulphate and zinc dust are weighed separately, the former is dissolved in water and the latter introduced into the solution of copper sulphate in small portions until it appears colorless. During the operation the vessel is freely shaken, lumps are comminuted with a glass rod, and a few drops of the liquid are ultimately tested with hydrogen sulphide or ammonia. The remainder of zinc dust is then weighed, and its value deducted from the original weight. Zinc and cadmium of the filtrate are determined as above. On repeating this method several times most satisfactory results are obtained. Another mode of operating is to employ an excess of copper sulphate and to determine the copper dissolved in the filtrate. The separation of copper from cadmium being difficult and laborious, and the volumetric estimation with potassium cyanide not practicable, it is not prudent to apply this method. When calcined zinciferous pyrites have to be examined, the estimation of zinc is similar to that employed in the analysis of zinc ore. The sample is exhausted with water, filtered, and, to eliminate calcium sulphate and basic iron sulphate, evaporated to dryness. It is then dissolved in a small quantity of alcohol and water, refiltered, and the filtrate decomposed with ammonium carbonate. The original residue is treated with a solution of ammonium carbonate, which dissolves arsenious acid and basic zinc sulphate, filtered, and united with the first filtrate. When iron and manganese are present, the filtrates are treated with bromine. The united filtrates are boiled or examined volumetrically with sodium sulphide. * * * * * PETROLEUM AS FUEL IN LOCOMOTIVE ENGINES.[2] [Footnote 2: Abstract of paper read before the Institution of Mechanical Engineers.] By Mr. THOMAS URQUHART.