Colored test papers

Papier-fabrik, /. paper factory, paper mill, -fabrikant, m. paper maker, -fabrikation, /. paper making, -farbe, /. paper color, -filter, n. paper filter, -flftche, /. paper sur-faee, surfaee of the paper, -gam, n. paper yarn, paper twine, -handel, m. paper trade stationery, -handlung, /. stationer s shop, -holz, n. pulpwood. -jod, n. a solution of iodine and potassium iodide for test paper, papierkaschiert, a. paper-covered, paper-baeked (as metal foil). 

The paper. strips used in the colorimetric method are impregnated with such dyes that the color of the test paper is dependent upon the pH of the medium in which the paper is placed. A standard color chart is supplied for comparison with the test strip. Test papers are available in a wide range type, which permits estimating pH to 0.5 units, and in narrow range papers, with which the pH can be estimated to 0.2 units. 

Into a conical flask, pipette a 50.0 or 100.0 mL aliquot of the solution and adjust the pH to 1-2 with aqueous ammonia solution (use pH test-paper). Add five drops of xylenol orange indicator and titrate with additional 0.05 M EDTA until the colour changes sharply from red to yellow. This gives the bismuth content. Record the total (combined) volume of EDTA solution used. Now add small amounts of hexamine (ca 5g) until an intense red-violet coloration persists, and titrate with the standard EDTA to a yellow end point the further consumption of EDTA corresponds to the lead-plus-cadmium content. 

Where definite loss of color by bleaching is noted, the content and container should be inspected to determine the cause. If correctable, such as a faulty gasket, broken container, etc, the gasket is changed or the powder is transferred to another container. A new strip of test paper is inserted and the proplnt replaced in storage with the container definitely marked to insure reinspection at the end of one year. 

Free nitrous acid causes an immediate blue color at the point of contact with starch-iodide test paper. A delayed color or a color around the periphery of the wetted area is of no significance. At all times there must be an excess of mineral acid (blue color on Congo paper). 

A simple, fast and specific color test for urea nitrate was reported recently by Almog et al. It is based on the reaction between urea nitrate and ethanolic solution ofp-dimethylaminocinnamaldehyde (p-DMAC) (9) under neutral conditions [91]. A red pigment is formed within 1 min from contact. Its structure has also been determined by the same group, by X-ray crystallography [92]. It appears to be a resonance hybrid between a protonated Schiffbase (10) and a quinoid system (10a) (Eq. (14)). The limit of detection on filter paper is 0.1 mg/cm. Urea itself, which is the starting material for urea nitrate, does not react with p-DMAC under the same conditions. Other potential sources of false-positive response such as common fertilizers, medications containing the urea moiety and various amines, do not produce the red pigment with p-DMAC. 

Elemental composition Na 58.93%, S 41.07%. An aqueous solution is analyzed to determine sodium content. Also, an aqueous solution may be analyzed for sulfide by methylene blue colorimetric test or by iodometric titration (APHA, AWWA, and WEF. 1999. Standard methods for the Examination of Water and Wastewater, 20 ed. Washington, DC American Pubhc Health Association). The methylene blue test is based on reacting sulfide, ferric chloride and dimethyl-p-phenylenediamine to produce methylene blue. Also, sulfide can be measured by using a sdver-sdver sulfide electrode. Quahtatively, sulfide may be identified from the hberation of H2S on treatment with acid. The H2S turns the color of paper soaked with lead acetate black (See Hydrogen Sulfide). 

Seifert (Ref 1) modified the test by introducing a test paper (methyl violet or rosaniline) and observing the successive changes of color Refs 1) Seifert, Voyenske-Technicke pravy (Prague), 4, 42 (1927) 2) Reilly (1938) p 79... 

Test tubes, each contg O.lg of a NC expl, are suspended in a bath of mineral jelly preheated to 100°. A strip of Kl-starch paper is suspended above the sample. Heating of the bath is continued, by raising the temp 5° per min, until the point is reached at which the test paper begins to color. This point is taken as an indication of the stability of the NC proplnt. 

Stability by Abel Test at 72. NGc colors KI paper quickly. However, this should be at-tributed to the. relatively high evaporation rate and slight dissociation of the vapors, and does not represent a low chemical stabiliry (Ref 7, p 226)... 

Note According to one of the Hercules Powder Co laboratory manuals, lead acetate is used in the prepn of test paper for detection of hydrogen sulfide. Strips of filter paper are dipped in 10% Pb acetate soln and then dried in atm free of HaS. The moist test paper, in the presence of even traces of HaS, gives a black color... 

Weigh to 0.1 mg 2.5 to 3 g of the purified aniline, transfer to a 1 1 volumetric flask contg 900 ml distd w and 50 ml coned HCl. Fill the flask to the mark and shake it until the soln is uniform. Transfer a 100 ml aliquot to a 400 ml beaker, add 10 ml coned HCI and cool the soln to 15°. Titrate slowly with the 0.2N KBrO,-KBr soln. Near the end of titration, test, after the addition of each drop of die soln, by spotting KI-starcH test paper. The end point is indicated by the It blue coloration which can be duplicated after a 2-tnin period. When the end point is reached, an addnl drop of the KBrOj KBr soln will color the mixt yel, thereby corroborating the end point indicated hy the test paper. Calculate the normality of KBrOs KBr by the following formula ... 

Carboxylic acids often have been identified by means of paper chromatography Clarke and Bazill (10) have extracted plasticizers from polyvinyl chloride first with ether and then with methanol. Subsequently the extracts were saponified with alcoholic potassium hydroxide, and the precipitated potassium salts were isolated and converted into free acids. These, in alcoholic solution, were then applied to paper and chromatographed ascendingly with a mixture of butanol, pyridine, water, and ammonia the migration period was about six hours. A number of additional color tests facilitated identification of unknown acids. 

YELLOW TURMERIC INDICATOR PAPER TURNS BROWN WITH BORIC ACID. YELLOW COLORING MATTER IN TABLE MUSTARD IS TURMERIC. TO MAKE TEST PAPER, DIP STRIPS OF PAPER TOWELING IN MUSTARD. WASH MUSTARD OFF. DRY STRIPS. 

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