Lead acetate paper

Sulphur. Moisten the centre of a filter-paper with lead acetate solution. Then add about 10 ml. of dilute hydrochloric acid to the residue in the evaporating-basin, and at once cover the latter with the paper. If zinc sulphide is present in the residue, the hydrogen sulphide evolved will give a definite daA brown coloration with the lead acetate paper. The presence of hydrogen sulphide can often be confirmed by its odour. 

Upon fusion with caustic alkah (for experimental details, see Section IV,33,2) and acidification of the aqueous extract, hydrogen sulphide is evolved (detected by lead acetate paper). This test is given by aU organic compounds of divalent sulphur (RSH, R SR" and R SSR"). 

When an organic compound is heated with a mixture of zinc powder and sodium carbonate, the nitrogen and halogens are converted into sodium cyanide and sodium hahdes respectively, and the sulphur into zinc sulphide (insoluble in water). The sodium cyanide and sodium hahdes are extracted with water and detected as in Lassaigne s method, whilst the zinc sulphide in the residue is decomposed with dilute acid and the hydrogen sulphide is identified with sodium plumbite or lead acetate paper. The test for nitrogen is thus not affected by the presence of sulphur this constitutes an advantage of the method. 

An Alka-Seltzer tablet gives off carbon dioxide when dissolved in aqueous solution. The gas is used to drive hydrogen sulfide out of drilling fluid samples. The H S then reacts with lead acetate paper in the bottle cap. The degree of discoloration is related to hydrogen sulfide concentrations. 

Do not rely on the sense of smell to detect hydrogen sulphide leaks. Strips of v/et lead acetate paper turn black on exposure to hydrogen sulphide and offer a simple indicator, as do colour indicator tubes. For plant-scale operations, instrumental multi-point detectors and alarms are likely to be more appropriate. 

Excretion of hydrogen sulfide was documented after dermal exposure in rabbits. Trunk fiir of rabbits was clipped and left intact or abraded for exposure to hydrogen sulfide gas (unknown concentrations) for 1.5-2 hours the animals then breathed clean air (Laug and Draize 1942). Evidence for the excretion of hydrogen sulfide by the rabbits was a sulfide reaction of the expired air with lead acetate paper (Laug and Draize 1942). Sulfides in the expired air were noted in one rabbit with intact skin after 7 minutes of exposure. This study was limited by the lack of measurement of exposure concentrations and the small number of animals used. 

In the lead acetate test (ASTM D2420), the vaporized gas is passed over moist lead acetate paper under controlled conditions. Hydrogen sulfide reacts with lead... 

Corrosive sulfnr componnds can be detected by their effect on copper and the form in which the general copper strip corrosion test (ASTM D1838) for petrolenm prodncts is applied to liqnefied petrolenm gas. Hydrogen sulfide can be detected by its action on moist lead acetate paper, and a procedure is also used as a measure of sulfur compounds. The method follows the principle of the standard Doctor test. 

The compound is treated with concentrated HCl H2S is hberated and is identified from its odor which also turns lead acetate paper black. The hberated H2S is transported onto a GC port by helium carrier gas and determined by an FID, TCD or FPD. Antimony in the solution may be analyzed by flame or furnace AA or by ICP spectrophotometry. The solid powder may be characterized by X—ray diffraction technique. 

Hydrogen Sulphide as an Acid. — In the anhydrous condition, whether as gas or liquid, hydrogen sulphide has no acidic properties. When moist or in aqueous solution, however, it behaves as a feeble acid, whence the occasional name hydrosulphuric acid. For the characteristic test with lead acetate paper or for the reddening of litmus paper, the presence of at least a little moisture is essential.3... 

Hydrogen Sulphide. — Heat 1 gm. of animal charcoal with 40 cc. of water and 10 cc. of hydrochloric acid, and test the escaping vapors with moistened lead acetate paper. The latter should not acquire a brown color. 

Lead Acetate Paper.—Used for detecting I S, with which it gives a brown coloration. Filter paper is soaked in a solution of 5 gms. lead acetate (or nitrate) per litre, and dried in an atmosphere free from H2S. Ferrous sulphate paper may also be used for detection of H S, but does not keep. 

Detection of Sulphur Dioxide.—This test is made on sugars from juices decolorised by means of sulphurous acid. To a solution of 10-15 grams of the sugar in about 25 c.c. of water in a flask are added a scrap of pure zinc (or 0-3-0-4 gram of magnesium wire) and 5 c.c. of pure hydrochloric acid. In presence of sulphur dioxide, hydrogen sulphide is evolved and may be detected by the odour or by means of a strip of lead acetate paper. 

Detection of Sulphur Dioxide.—Sulphurous anhydride, which is often added to tanning extracts, either as such or more often as sulphites, to enhance their keeping qualities, may be detected by treating 10 grams of the extract in a beaker with 20 c.c. of hydrochloric acid and 20 c.c. of water, a piece of pure zinc being added and the beaker covered with a clock-glass under which is suspended a strip of lead acetate paper if the extract contains sulphurous anhydride, the paper becomes brown or assumes a blackish tint with metallic reflection. If the paper remains white for 15 minutes, absence of sulphurous acid may be assumed. 

Lead acetate paper test. A paper moistened with lead acetate solution turns black due to the formation of lead sulfide on exposure to H2S. 

Dilute hydrochloric acid or sulfuric acid Silver nitrate Lead acetate Sodium nitroprusside solution Sulfides, S2 Hydrogen sulfide gas is evolved and detected by odor or lead acetate paper Black precipitate of silver sulfide soluble in hot, dilute nitric acid Black precipitate of lead sulfide Transient purple color in the presence of solutions of alkalis... 

Hydrogen sulfide gas evolved, detected by holding lead acetate paper to mouth of test tube Evolution of sulfur dioxide gas Red compound of unknown composition... 

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. 

Reducing Sugars Dissolve 500 mg of sample in 10 mL of water, warm, and make the solution alkaline with 1 mL of 6 N ammonium hydroxide. Pass hydrogen sulfide gas into the solution to precipitate the iron, and allow the mixture to stand for 30 min to coagulate the precipitate. Filter, and wash the precipitate with two successive 5-mL portions of water. Acidify the combined filtrate and washings with hydrochloric acid, and add 2 mL of 2.7 N hydrochloric acid in excess. Boil the solution until the vapors no longer darken lead acetate paper, and continue to boil, if necessary, until the solution has been concentrated to about 10 mL. Cool, add 5 mL of sodium carbonate TS and 20 mL of water, filter, and adjust the volume of the filtrate to 100 mL with water. Add 2 mL of alkaline cupric tartrate TS to 5 mL of filtrate, and boil for 1 min. No red precipitate forms within 1 min. 

No studies were found that examined excretion in humans after dermal exposure to hydrogen sulfide. One study conducted in rabbits provides evidence of excretion of hydrogen sulfide after dermal exposure (Laug and Draize 1942). The fur on the trunk of the animals was clipped, left intact, or abraded and then the animals were exposed to hydrogen sulfide (concentration not reported) for 1.5-2 h. The animals were then exposed to clean air. Expired air from the animals reacted with lead acetate paper, indicating the presence of sulfide (Laug and Draize 1942). 

Zinc and sulphuric acid hydrogen sulphide gas is evolved, which may be detected by holding lead acetate paper to the mouth of the test-tube (cf. Section IV.6, reaction 1) ... 

The characteristic colours and solubilities of many metallic sulphides have already been discussed in connection with the reactions of the cations in Chapter III. The sulphides of iron, manganese, zinc, and the alkali metals are decomposed by dilute hydrochloric acid with the evolution of hydrogen sulphide those of lead, cadmium, nickel, cobalt, antimony, and tin(IV) require concentrated hydrochloric acid for decomposition others, such as mercury(II) sulphide, are insoluble in concentrated hydrochloric acid, but dissolve in aqua regia with the separation of sulphur. The presence of sulphide in insoluble sulphides may be detected by reduction with nascent hydrogen (derived from zinc or tin and hydrochloric acid) to the metal and hydrogen sulphide, the latter being identified with lead acetate paper (see reaction 1 below). An alternative method is to fuse the sulphide with anhydrous sodium carbonate, extract the mass with water, and to treat the filtered solution with freshly prepared sodium nitroprusside solution, when a purple colour will be obtained the sodium carbonate solution may also be treated with lead nitrate solution when black lead sulphide is precipitated. 

The test is usually carried out by adding the reagent to the solution acidified with dilute hydrochloric acid carbonates, sulphites, and phosphates are not precipitated under these conditions. Concentrated hydrochloric acid or concentrated nitric acid should not be used, as a precipitate of barium chloride or of barium nitrate may form these dissolve, however, upon dilution with water. The barium sulphate precipitate may be filtered from the hot solution and fused on charcoal with sodium carbonate, when sodium sulphide will be formed. The latter may be extracted with water, and the extract filtered into a freshly prepared solution of sodium nitroprusside, when a transient, purple colouration is obtained (see under Sulphides, Section IV.6, reaction 5). An alternative method is to add a few drops of very dilute hydrochloric acid to the fused mass, and to cover the latter with lead acetate paper a black stain of lead sulphide is produced on the paper. The so-called Hepar reaction, which is less sensitive than the above two tests, consists of placing the fusion product on a silver coin and moistening with a little water a brownish-black stain of silver sulphide results. 

CdS and excess of CdC03. Wash and reject washings. Digest residue with dilute acetic acid to remove excess carbonate. A yellow residue indicates sulphide. Confirm by warming with dilute HC1 and test the evolved H2S with lead acetate paper. Add Sr(N03)2 solution in slight excess, shake, allow to stand overnight and filter. ... 

Hydrogen sulphide is evolved (odour of rotten eggs turns lead acetate paper black or cadmium acetate paper yellow). 

Boil down in a porcelain dish to about 10 ml and thus ensure that all H2S has been removed (test with lead acetate paper). Add 3-4 ml concentrated HN03 to oxidize any Fe2+ to Fe3+ etc. (5), and evaporate cautiously to dryness moisten with 2-3 ml concentrated HN03 and heat gently this will remove organic acids. 

---