Thursday, July 21, 2011

DETECTION OF METALS

          The extraordinary progress made in histochemical analysis during recent years deserves the attention of all textile chemists,especially since the development of spot tests has placed a large number of very successful reactions within reach of almost anyone . They may be divided into three main groups :

( 1 ) Crystal formation tests.
 These involve the precipitation usually on a microscope slide of a chemical compound which has a distinctive cry stalling form or colour the crystals are as a rule of micro dimensions and in some instances require high magnification for observation . Although very sensitive and specific they require some skill and experience and knowledge of crystallography.

( 2 ) Stop tests
 which involve the production on a glass plate or filter paper of a coloured stain or precipitate which is characteristic of a certain radices or element . They are very simple to carry out and are superseding many old established tests.

( 3 ) Film tests
 These depend on the taking of a print on gelatine film previously impregnated with a suitable reagent. The film is pressed into contact with the material such as cloth which it is desired to test.

SODIUM SULPHATE
This is marketed as salt cake glanders  salt and sodium sulphate crystals .It should be tested colorimetric ally for iron and volumetrically for sulphate content by precipitation as Benzedrine sulphate or alternatively as barium sulphate by the gravimetric method.