Some American-Made Chemical Reagents
Journal of Industrial & Engineering Chemistry
ble in the usual way. When all t h e soluble material had been removed, except t h e small amount in the upper rim. the cri~rihle was f l l d about half full of water, suction was applied and a moistened rubber stopper was quickly pressed down on top of the crucible. (The rubber stopper was always polished to a plane surface and washed free from any dust before using t h e first time.) As soon as t h e stopper was firmly held by t h e suction, water was poured on top of t h e holder (see
... holder (see figure) and around the stopper. The water drawn through t h e top rim easily completed t h e washing, as was indicated by the fact t h a t no test for alkalinity could be obtained by addition of a drop of phenolphthalein t o t h e edge of the crucible. Continuous use of t h e crucible holder, since i t was not designed for treatment in this manner, tended t o crack t h e flange from t h e outer portion of t h e holder. A slight modification of t h e flange construction would perhaps lessen this difficulty. they were of the same quality, but a single recrystallization from a filtered solution gave a perfectly satisfactory product. Correspondence with manufacturers and dealers secured some analytical reports which indicated material of high purity. A sagnple furnished as representing the product now sold by one manufacturer made a perfectly clear I O per cent solution with no traces of green color and no precipitate. It therefore appears t h a t no one need now accept potassium ferricyanide which will not make a I O per cent solution without any precipitate or green color. Purification of poor material in stock is worth while in most cases. 11-METHYL O R A N G E ' Similar complaint was made t o t h e Committee of difficulty in procuring satisfactory methyl orange from American manufacturers. At t h e suggestion of t h e Committee, samples were purchased from four different sources. There was at hand for comparison one of a well-known foreign make. A sixth sample was obtained from a lot of methyl orange which was exhibited by a manufacturer a t a meeting. A few grams of t h e best appearing sample (Sample A) were repurified by precipitating the free acid, filtering, dissolving with sodium carbonate solution, and recrystallizing twice. This produced shining crystal leaflets of a beautiful orange-red color which RAPID DETERMINATION OF SMALL AMOUNTS OF COPFER BY THE IODIDE METHOD The precipitate of cupric sulfide (containing not over 0.05 g. copper) is washed free from chlorides (complete removal of iron not being necessary), then moistened with a few drops of strong neutral zinc nitrate solution (free from chlorides), and ignited. The residue of zinc oxide and cupric oxide is quickly dissolved by warming with I cc. of I : 2 hydrochloric acid. Neutralize with 5 per cent potassium hydroxide, acidify with acetic acid, add a little phosphate solution t o prevent the action of iron,l then add 2.5 g. solid sodium iodide and titrate as usual.