. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . hich are suspended slips of bibu-lous paper impregnated with the basic acetate oflead (i part of sugar of lead to 8-9 parts of water).Such papers become darkened in the presence of sul-phuretted hydrogen, &c., in degree varying with theamount of this agent present; the faintest indicationwill generally be found in a slight discoloration of theextreme margin of the papers. Sulphurous acid, and sulphur compounds other than sul- «
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . hich are suspended slips of bibu-lous paper impregnated with the basic acetate oflead (i part of sugar of lead to 8-9 parts of water).Such papers become darkened in the presence of sul-phuretted hydrogen, &c., in degree varying with theamount of this agent present; the faintest indicationwill generally be found in a slight discoloration of theextreme margin of the papers. Sulphurous acid, and sulphur compounds other than sul- « For the illustrations of apparatus required in gas analysis, I amindebted to William Sugg and Co., Gas Engineers, London. ANALYSIS OF COAL GAS. 247 phuyetted hydrogen.—These are estimated by collectingthe sulphur as sulphuric acid, into which it is convertedby combustion ; precipitating this by baric chloride asthe sulphate of baryta, and then estimating the sulphurin the precipitate (of BaSOJ. The gas is passed through a meter, by means of whichthe rate of flow can be adjusted and registered to half acubic foot per hour, and in which a self-acting move-. OM B Fig. 39.—Apparatus for testing the presence of sulphuretted hydro-gen. ment shuts off the gas when 10 cubic feet have passedthrough. The meter employed is shown in figure dial of the meter is divided into 100 parts, andeach complete revolution of the index hand representsthat one cubic foot of gas has passed through theapparatus; and each division, therefore, representsy^Q of a cubic foot. The position of the long index handon the dial must, accordingly, be carefully noted at thecommencement of each test. 248 LABORATORY WORK. When making the estimation no other gas should beburning in the same room, and, according to the direc-tions of the Referees, the gas (which has been freed fromsulphuretted hydrogen) is to be burnt in a small Bunsenburner mounted upon a short cylindrical stand (figs. 41and 42), perforated
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