Saturday, January 29, 2011

ANALYTICAL TESTS:

Burning test :
              
                 A small portion of cloth treated with synthetic resin is held to a Bunsen flame , and withdrawn after ignition. This test is of most value with coated fabrics on which there is a substantial amount of coating.
When only small percentages of resin are present, indications are often rather vague. Cellulose nitrate is very inflammable . Rubber has a characteristic  dour. Oxidized oil burns with a fatty smell.
The various odours indicated in test 3 may be recognized under favorable circumstances.

Sodium Fusion 
                
                    This should be the basis of the qualitative analysis of an unknown resin.It is carried out as in qualitative organic analysis by heating about 0.5 gm. cloth with a small pea-size piece of metallic sodium in a hard glass tube. Springy cloth may be cut into small shreds, made into a ball with very stiff methyl cellulose mucilage, and dried before carrying out the test. Alternatively, the cloth may be charred at low heat, and after cooling the tube to room temperature, the sodium may be added. After fusion, the red-hot tube is dropped into an evaporate- ing dish containing a few c.c. of distilled water ; this should be done at arm,s
length, with suitable precautions against possible flying sodium. The test is dangerous if cellulose nitrate is suspected; this is liable to explode. The following tests are carried out for the detection of elements.

   Cblorine. To a small portion of the extract add a little silver nitrate solution; a white precipitate of silver chloride ( which blackens on exposure to light ) indicates chlorine, which may be from chloroprene,
chlorinated rubber, chlorinated diphenyl, polyvinyl chloride, or poly-vinylidene chloride. A very beavy precipitate may indicate chlorine-ated rubber ,which contains up to 60% of chlotine.

Nitrogen. To a portion of the extract add a little ferrous sulphate ( containing a little iron oxide in suspension) and warm with nitric acid.A bluish-green colour or precipitate of Prussian Blue indicates nitrogen, which may be from aniline /formaldehyde, cellulose nitrate, melamine/formaldehyde, polyacrylonitrile, resins urea/formaldehyde, thiourea/formaldehyde.
  Add 2 c.c. of extract to 10 c.c.of ammonium moderated in nitric acid solution .A yellow precipitate of ammonium phospho-molybdate,soluble in alkalis, indicates phosphorus, which may be from casein ( or, more rarely, from certain unusual textile auxiliaries).This is the best distinguishing test between lanital and such other protein plastics; it distinguishes between lanital and such fibres as Ardil.