Lead Acetate Yellow

Lead acetate Yellow precipitate of lead chromate soluble in dilute nitric acid insoluble in acetic acid... 

Chromates.—(1.) HaS in acid solution, brownish color, changing to green. (3.) Ammonium sulfhydrate, greenish ppt. (3.> Barium chlorid, yellowish ppt. (4.) Silver nitrate, brownish-red ppt., soluble in HNOsOr KHtHO. (5.) Lead acetate, yellow ppt.> soluble in potash, insoluble in acetic acid. 

Needles from HjO. M.p. about 165° deooin Very sol. EtOH, AcOH. Less sol. HjO. HJ, or Ac,0 —> iocoumarin. Aik. K, e(CN)g. —> thionaphthene. NaHg —2-meroapto-hydrocinnamio add. Lead acetate —> yellow ppt. 

Allow the reddish-yellow solution to cool to about 40° and then filter off at the pump the polyene which has separated this filtration should be performed as rapidly as possible to avoid contamination with lead acetate, and a Buchner funnel of not less than 6 cm. diameter should therefore be used to avoid clogging the filter. Wash the crude production the filter with... 

Identification. When a solution of ferric chloride is added to a cold, saturated vanillin solution, a blue color appears that changes to brown upon warming to 20°C for a few minutes. On cooling, a white to off-white precipitate (dehydrodivanillin) of silky needles is formed. Vanillin can also be identified by the white to slightly yellow precipitate formed by the addition of lead acetate to a cold aqueous solution of vanillin. 

Tests for Caramel.—Valuable indications of the nature of an extract are obtained in the process of determination of vanillin and coumarin. Pure extracts of vanilla beans give, with lead acetate, a bulky, more or less glutinous, brown-grey precipitate, and a yellow or straw-coloured filtrate, whereas purely artificial extracts coloured with caramel give a slight dark brown precipitate and a dark brown filtrate. If both vanilla bean extract and caramel are present the precipitate is more or less bulky and dark coloured, and the filtrate is more or less brown. The soluticm remaining after extraction of the vanillin and coumarin with ether, if dark coloured, should be tested for caramel. 

Lead Oxide, Yellow, or Litharge (Lead Monoxide, Lead Protoxide or Plumbous Oxide). PbO, mw 223.21, yellow to yellowish-red, heavy, odorless pdr or minute, cryst scales mp 888°, bp (vol at red heat) d 9.53g/cc insol in w, ale sol in acet ac, dil nitric acid, in warm solns of fixed alkali hydroxides. It may be prepd in the lab by heating Pb nitrate, carbonate or hydroxide commercially, it is made by heating Pb to a temp considerably above its mp and continually skimming off the litharge produced. It is used in some primer compns... 

Prepare about 30 g. of normal lead chromate, PbCr04 (Exercise 23), by the double decomposition of lead acetate and potassium dichromate and wash the precipitate until it is free from soluble lead salts. Suspend the yellow chromate in a dilute solution of sodium hydroxide (1 20) and boil until the color has changed to a bright brick red. This material is a basic chromate known as chrome red, having the composition represented by the formula PbCr04-PbO ... 

Lead Selenocyanate has been obtained as a lemon-yellow compound by the action of lead acetate on potassium selenocyanate. It is soluble in boiling water but is slightly decomposed. The salt may be exposed without decomposition to a temperature of 100° C., but when moist assumes a pink tint.1... 

Lead Metavanadate, Pb(VOg)2.—Acid solutions of vanadates on being treated with lead salts give rise to yellow basic vanadates the composition of which varies with the conditions. The precipitation of normal lead vanadate is, therefore, difficult. It has been accomplished by the addition of lead acetate to ammonium metavanadate solution in the presence of acetic acid.2 The lead precipitates contain all the vanadic acid originally present in solution, and precipitation of vanadates with lead salts has, therefore, been employed for the quantitative estimation of vanadium.3 The mineral deschenite consists chiefly of lead metavanadate a portion of the lead is, however, frequently replaced by zinc.4... 

Lead Pyroarsenite, Pb2As205, is a white powder formed by decomposing normal lead acetate with amnioniacal arsenious oxide solution,7 or with potassium tetrarsenite8 or pyroarsenite,9 According to Simon,10 it is also formed by the combination of arsenious oxide vapour with lead oxide Stavenhagen,11 however, found the product to be merely a mixture of oxides. When heated, lead pyroarsenite fuses to form a yellow glass. It liberates ammonia from ammonium salts even in the cold. 

A colloidal solution of lead arsenite has been obtained by the following method. A solution of lead acetate is treated with a 10 per cent, solution of sodium lvsalbinate, and after washing the precipitate with hot water, it is dissolved in a dilute aqueous solution of sodium hydroxide containing sodium dihvdrogen arsenite. The liquid, after keeping for some hours, is filtered and dialysed until the outside liquor is free from arsenic. The solution in the dialyser is concentrated, mixed with alcohol and ether, and dried over sulphuric acid in a vacuum. A pale yellow horny mass remains, which dissolves readily in water to form a sol.3... 

Cyclodesulfurization of thioureide 213 with lead acetate or yellow mercuric oxide in methanol, followed by acetylation with acetic anhydride, affords two products, acetylaminobenzimidazole and (glycosylamino)benz-imidazole 216 however, the latter was formed in very poor yield.99 The... 

GelatiAe.—5 grams of the powdered chocolate are treated with 50 c.c. of boiling water, 5 c.c. of 10% lead acetate solution being then added and the liquid filtered. The filtrate is tested with a few drops of saturated aqueous picric acid solution in presence of gelatine, a yellow precipitate forms. 

A yellow coloration of the fused mass indicates chromium. The mass is taken up in the platinum dish with water and acetic acid then added a little at a time until the reaction is acid. In a small portion of the acetic acid solution the presence of chromium may be confirmed by means of lead acetate. The acetic add solution and any undissolved part of the mass are concentrated to a small volume in a porcelain dish over a naked flume and then taken to dryness on a water-bath. The residue is heated for some time in an air-oven at iio° and then treated with water and hydrochloric acid and filtered. The filtrate is tested for tin and copper by means of hydrogen sulphide. 

The former is deposited in yellow crystals, mixed with sulphur when acetoxime is treated with phosphorus pentasulphide in carbon bisulphide soln. the insoluble product extracted with alcohol and the alcoholic soln. heated to boiling the compound separates from cold water in large, transparent, seemingly monoclinic prisms, melts at 146° 150° with decomposition, and is readily soluble in water, but only sparingly in alcohol, and insoluble in ether and carbon bisulphide. It decomposes carbonates, gives a colourless precipitate with lead acetate, and is decomposed by hot dilute nitric acid with separation of sulphur and formation of phosphoric acid it is also decomposed by mercuric oxide, the filtrate from the precipitated mercury sulphide giving all the reactions of phosphoric acid. 

Paper tape H2S analyzers use paper strips treated with lead acetate colored stains of PbS detected by photocells (Kimbell, 1982) color ranges from light yellow to silvery black extremely high signal amplification required to measure stains far too hght in color for rapid and continuous measurement of II2S at low ppb level. 

Lead acetate Potassium dichromate and concentrated sulfuric acid Sodium nitrite Copper sulfate Mercury (II) chloride Yellow precipitate of lead iodide soluble in excess hot water Liberation of iodine Liberation of iodine Brown mixed precipitate Scarlet precipitate of mercury (II) iodide... 

Melanin compounds may appear brown, black, or red. The type of melanin determines hair color, and the density of melanin granules determines the shade. Dark shades of dyed hair contain higher concentrations of dyes. Most hair colors are combinations of organic compounds chosen to produce particular shades. Resorcinol produces a yellow color aminohydroxy-toluene produces a redder hair, and nitrophenylenediamine dye results in very red hair. Graded dyes favored by men often contain lead acetate. The lead ions penetrate into hair and form lead sulfide (PbS), a dark-colored compound. 

As in Experiments 12 and 13 the solid effervesces in the concentrated sulphuric acid and the gas evolved fogs the breath (even more markedly in this case), turns litmus red, and gives a dense smoke with ammonia. When the tube is warmed, the beautiful purple iodine vapor is seen inside and nearly black crystals collect on the cooler upper walls. Lead acetate paper is colored dark brown. Sometimes a powdery light yellow substance (sulphur) is seen collecting on the walls of the tube. 

Lead Platinocyanide, PbPt(CN)4, is readily prepared by mixing boiling saturated solutions of potassium platinocyanide and lead acetate. The solution remains clear, but on cooling the lead salt separates out as a yellowish white crystalline powder.4 It is anhydrous, and becomes yellow on warming in air, then white whilst at higher temperatures cyanogen is liberated, the residue containing metallic lead and platinum. 

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