Paper yellowing

The liberation of hydrocyanic acid due to complete hydrolysis of cyano-genic glycosides can be determined by a simple colour test using sodium picrate paper (yellow), which turns red (sodium isopurpurate) in contact with HCN. 

Numerous cationic azo dyes are prepared by the action of /V-hydroxymcthyl-chloroacetamide on azo dyes in sulfuric acid medium, followed by displacement of the reactive chloro substituent by pyridine or trialkylamine. Of special significance for dyeing paper are dyes that are prepared by coupling of diazotized 2-(4 -aminophenyl)-5-methylbenzothiazole to acetoacetaiylides, pyrazolones, naphthols [143], or barbituric acid derivatives [144], followed by reaction with N-hydroxymethylchloro-acetamide and pyridine. The azo dye obtained by oxidative dimerization of 2-(4 -aminophenyl)-5-methylbenzothiazole may also be subjected to this conversion [145], Dye 51 colors paper yellow. 

A Reexamination of Paper Yellowing and the Kubelka—Munk Theory... 

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

Colourless gas evolved odour of rotten eggs blackens filter paper moistened with lead acetate solution turns cadmium acetate paper yellow. 

Phenol Red. The first publications of an automated procedure for the measurement of cholinesterase inhibitors are those of Winter 14) and Winter and Ferrari (15). The method employed an Autoanalyzer instrumental system wherein the extracts containing the insecticide were incubated with a standard cholinesterase solution at 37 °G. A continuous sample from the incubation bath is buffered and mixed with acetylcholine iodide. After a second incubation, the acetic acid released by the action of the uninhibited cholinesterase is measured colorimetrically, using phenol red as the indicator. More recently, Fischl et al. 16) reported a method for rapid detection of organic phosphate pesticides in serum. Strips of filter paper were impregnated with a buffered acetylcholine substrate solution containing phenol red as an indicator. When no inhibition is present, the acid released from the action of cholinesterase turns the paper yellow. When cholinesterase has been inhibited, the paper turns pink-to-violet. 

Durbeej, B., and Leif A. Eriksson. 2005. Photodegradation of substituted stilbene compounds What colors aging paper yellow J. Phys. Client. A, 109(25) 5677-5682. 

The alkylation process enters into dye manufacture in two ways, because dyes may be formed from alkylated intermediates, or in a lesser numt>er of instances, an intermediate may be subjected to alkylation as a final step. For instance, dimethylaniline is condensed with phosgene to give tetra-methyldiaminobenzophenone (Michler s ketone). From this ketone are formed many dyes, such as crystal violet and Victoria blue. On the other hand, the alkylation process may be almost the last step in the manufacture of a dye, for example, when the disazostilbene dye, paper yellow 3G, is ethylated to give crysophenine G. 

Cresyl Orange and filter paper Pre-cut strips of white filter paper are saturated with a few drops of cresyl orange liguid which turns the white paper yellow. Expose the paper to the inside of the Phase II room or to the exhaust air of the bulk room. The paper can also be... 

Other Names Brilliant Yellow C C.I. Direct Yellow 4 C.I. Direct Yellow 4, disodium salt Benzo Brilliant Yellow Brilliant Fast Yellow G2N Brilliant Paper Yellow Brilliant Paper Yellow C Brilliant Paper Yellow P Brilliant Yellow Brilliant Yellow (indicator) C.1.24890 Calcomine Brilliant Paper Yellow Chlorazol Brilliant Yellow 3G Diaphtamine Brilliant Fast Yellow 3G Diazol Brilliant Yellow N Direct Brilliant Yellow G Direct Yellow 4 Fenamin Yellow 3G Kayaku Direct Yellow G Nippon Brilliant Yellow G Paper Yellow 3GX Paper Yellow 3GXA Paper Yellow CB Tertrodirect Yellow B Trisulfon Paper Yellow... 

Yellow or brown vapors. Bromine derived from bromides in the presence of oxidizing agents nitrogen oxides derived from nitrates or nitrites chromyl chloride, provided both bichromate and water-containing chlorides are present. (Bromine vapors turn starch paper yellow in contrast to nitrogen oxides that have no visible action on this paper.)... 

Evolved ammonia (i) turns litmus blue (ii) forms white NH4CI fumes (iii) turns paper black (iv) turns paper yellow>brown (v) pH>7. 

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