Tuesday, January 4, 2011

SULPHURIC ACID TEST :


Some fabric is heated with 20% H2 so4; cool dilute, diazotise by
addition of a little sodium nitrite, couple with alkaline Rsalt solution : 
red indicates aniline from aniline formaldehyde resins. some of 
the above uniazotised solution is steam destilled into liebermann storch reagent; 
return of coloul may indicate a urea formaldehyde resin.

Fuse a little cloth with na OH, extract with water , add to about IO
c.c. of extract, two drops of a I% suspension in water of dinrom- quinone 
chlorimide; add oI % naOH solution drop by drop to ph 9.4; blue purple 
indicates phenols, cresols , xylenols and their p-tert- alkyl derivaties.

The fabtic is steeped for one hour in a saturated aqueous solution of the resgent, 
then for fifteen minutes in 20 vol. hydrogen peroxide:
mauve- brown indicates cellulose fibres and urea formaldehude resins; 
yellow indicates thermoplastic resins.


Alittle fabric is steeped for several hours in a cold soluion of kiton blue v at
ph 3.1; blue indicates lignified celluloses, urea form aldehyde resins ,and 
polyamides; no colour indicates cellulose fibres and phenol-formaldehyde types.

 (A) Scbiff;s reagent, see test 13. (b) A small piece of cloth 
is placed in 2 c.c. of 66% v/v H2SO 4,and a few crystals of cbromotropic acid heat 
at 60-70 deg, c. for ten minutes: bright violet indicates formaldeghde. 
A blank is necessary to allow for impurities in the air. (C) scbryver's 
test; to 5 c.c of solution prepared by hydrolysing resin coated fabric with 
2% HCI at the boilfor ten minutes, add I c.c. fp freshly prepared I% 
phenylhydrazine hydrochloride stand two to three minutes, add I C.c.5% 
potassium ferricyanide and 5 c.c. conc. HCI : purple red indicates formaldehyde.  
(D)To 5 c.c. of hydrolysate (as test (C) add a little pbloroglucinol and neutralise 
with NaOH : deep red indicates formaldehyde.

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