Testing                                                                                                                                              COPPER NUMBER

Copper Number

Principle of the Method

The copper number of paper is defined as the number of grams of metallic copper in the cuprous oxide resulting from the reduction of copper sulphate, under the conditions of this method, by 100 g of the paper.

The copper number may be regarded as an index of those impurities in cellulose, such as oxycellulose, hydrocellulose, lignin and sugars, which possess reducing properties. It is valuable for detecting changes accompanying deterioration and may, therefore, be considered as a test for indicating the permanence of paper.

Apparatus

The apparatus shall consist of the following:

Grinder - a grinder that will completely disintegrate the paper without heating or contaminating it. The grinder shall be a Koerner type or its equivalent.

Reagents

Copper Sulphate Solution - Dissolve 100 g of copper sulphate crystals (CUS04, 5H20) in water and dilute to one litre.

Carbonate-Bicarbonate Solution - Dissolve 350 g of sodium carbonate powder (Na2C03, 10H20) or 129 g of anhydrous sodium carbonate (Na2 COS) and 50 g of sodium bicarbonate (NaHC03) in water and dilute to one litre.

Molybdophosphoric Acid - Dissolve 100 g of sodium molybdate crystals (NaMo04, 2H20) and 75 ml of phosphoric acid (83 percent) in a mixture of 275 ml of sulphuric acid (sp gr 1. 84) and 1. 75 litres of water.

Sodium Carbonate Solution - approximately 5 percent (w/v) in water.

Calculation

Calculate the copper number as follows:

                                                  6. 36 V N 

Copper number =                    ——————

                                                       W

where V = volume in ml of potassium permanganate solution required for the titration;

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