CHEMISTRY: Analytical) .
3o. Drying oven. The hole at the top carries a cork through which a thermometer is in serted. Material to be dried is placed (in a suitable con tainer) on the tray. The holes in the tray allow the sterns of funnels (holding filter paper) to be inserted.
A burner is placed under the oven. Similar ovens may be heated electrically. A steam oven is similar but is sur rounded by a "jacket" in which steam circulates.
31. Gooch crucible with rubber cone, glass adapter and filter flask. The bottom of the crucible is perforated with small holes, and a mat of asbestos is formed on it by pouring in a pulp of asbestos and water, sucking it nearly dry and completely drying it in the oven. Used for filter ing, washing, drying and weighing precipitates.
32. Carbon dioxide apparatus (Schrotter) . The apparatus is weighed with all constituents separated ; the hydrochloric acid (HC1) is then allowed gradually to flow on to the solid; the carbon dioxide (CO2) given off carries some aqueous vapour which is retained by the concentrated sulphuric acid (H2SO4), and after warming, cooling and passing air through to displace all the carbon dioxide, the apparatus is reweighed, the loss of weight being due to the carbon dioxide given off.
33. Apparatus for detection and estimation of traces of arsenic (Thorpe) . The suspected material is treated so that its arsenic is obtained in acid solution, which is electrolysed and thereby reduced to arsine, AsH3 ; this is dried by calcium chloride and purified by lead acetate in tube A, and decomposed by heat from a micro-burner B ; it then deposits arsenic as a "mirror" at C, the density and colour (yellow, brown or black) depend ing upon the amount of arsenic.
34. Standard flask. Contains the stipulated volume when filled to the mark with a liquid at 15° C. Used for preparing "standard" solutions, i.e., those containing a definite quantity of solid dissolved in, e.g., 1,000 cu.cm. of solution.
35. Mouth blowpipe ; used for directing a small flame jet on to the substance being analysed (usually supported on a block of charcoal) .
36. Crucible tongs ; may be tipped with platinum for refined work. These should be placed with points upwards, so as to avoid contamination such as would occur if the points were down wards touching a working-bench.
37. Pipettes (not to scale) . (a) If filled exactly to the mark by suction, will then deliver the stipulated volume on draining for 15 seconds after continuous flow has ceased. (b) Can be used for gradual addition of small quantities which are read off on the scale.
Special Apparatus.
38. Victor Meyer apparatus. A liquid such as aniline is kept boiling in the outer bulb. The side arm holds a small stoppered tube containing a weighed quantity of a liquid. When the apparatus ceases to emit bubbles of air, the small tube is tipped into the inner bulb (a little sand or mercury being present to break the fall and save fracture), and the vapour of the liquid displaces its own volume of air, which ascends the eudiometer, displacing water or mercury, and is there measured. Vapour densities are thus determined (see ASSOCIATION ; and STOI CHIOMETRY) .
lo. Soxhlet extractor. The material to be extracted (crushed seeds or cocoa) is placed in a "thimble" of filter paper. Ether is boiled in the flask, passes by the side tube A to the reflux condenser C, the liquid drops into the thimble where it accu mulates till it reaches the level of the top of the side arm B, and then siphons over to the flask. Several extractions remove all the fat, which can then be weighed in the flask if all the ether is evaporated from the flask through a non-return con denser.
40. Beckmann thermometer (top only) . For showing small tem perature changes (of 5° or less) with an accuracy of 000i° C. By taking mercury from, or returning it to, the reservoir, the range can be altered at will. (A. D. M.)