Fume fading

EDS analysis of yam cross sections could provide additional information, and document, for example, whether sulfur from the air permeates the fibrous core as well. Such is the case in the fume fading of textiles enclosed in environments with sulfur and nitrogen oxides. Elemental mapping of the fiber cross sections would show the depth of penetration of the absorbed or adsorbed species, and perhaps indicate the length of exposure, as well as of exposure to gaseous rather than aqueous environments. 

Cellulose acetate and triacetate can be spun-dyed. Spun-dyed acetate and triacetate yarns are extremely colorfast to washing, dry cleaning, sunlight, perspiration, sea water, and crocking and are very resistant to gas or fume fading [15]. 

Rather than dipping the chromatogram in acid solution it is preferable to heat it to 100°C for 2—5 min (fume cupboard ) in order to evaporate the ammonia and turn the background yellow. By this means it is possible to increase the sensitivity of detection for some of cations e.g. Sr and Ba. However, these zones fade after some time, so that it is necessary to quantify the chromatogram immediately after heating. 

On the other hand, when paper strips with benzoazurine, trypan red or ethyl violet were exposed to unstable double-base propint, or to nitrogen oxide fumes prepd in the lab, all of the papers either bleached or faded, as did the methyl violet paper... 

However, strips of the experimental indicator papers, when exposed to oxides of N fumes generated in the lab and to double-base proplnt fumes generated at an elevated temp, became either entirely bleached or totally faded Refs. l) S. Helf, PATR 1782 (Oct 1950) 2 ... 

Take a red rose that is quite faded, and put a little sulphur on a chafing-dish of hot coals then hold the rose over the fumes of sulphur, and it will quickl become white in this state dip it into water, then put it in a box or drawer for three or four hours, and when taken out it will be quite red again. 

The most frequently used color reactions are those developed by Vital and Gerrard and may be briefly described as follows The Vitali Reaction (1). A minute quantity (as little as 0.0001 mg. is sufficient) of solid atropine, Z-hyoscyamine or Z-scopolamine, on a watch glass, is treated with a drop of fuming nitric acid and the liquid evaporated to dryness at 100°. The residue when treated with a drop of freshly prepared solution of ethanolic potassium hydroxide develops a bright purple coloration which slowly fades to a dark red and finally to a colorless liquid. The color sequence can be reproduced by the addition of more potassium hydroxide reagent. 

Nitrous acid, a moderately strong acid, has not been isolated. Its aqueous solution, freshly prepared by adding N2O3 to cold water, is blue, but the color soon fades and brown fumes (from NO + O2 forming NO2) are released ... 

Weigh out accurately about 0.5 g of any of your preparations in a conical flask. Add 20 cm of dil. NaOH and heat on a sand bath in the fume cupboard to distil off the NH3 liberated. A suspension of black C02O3 remains in the flask. Cool under the tap and filter through GF/C filter and wash well with H2O. Transfer the filter quantitatively to a clean conical flask, add 1.5 g Kl and acidify freely with dil. HCl. Cover with a watch glass and allow to stand until all the black particles have dissolved. Titrate the liberated I2 with standardised 0.1 M Na2S203 solution until the colour fades to straw yellow. Dilute with H2O to 200 cm and add 2 cm freshly prepared starch solution. Continue the titration carefully until the dark blue starch/l2 adsorption complex disappears for 1 minute. At the end-point the pale pink colour of Co(Il) remains in solution. Repeat and calculate from each result the % Co in your preparation and hence its % purity. 

---