The controlling factors and Chemicals-auxilaries used in Liming process

Controlling factors of liming process

1. pH: In this operation, pH maintains 12.5 - 13 and that is why limed pelt is swollen. 
2. Temperature: Temperature plays an important role in liming. Too high temperature will cause hide degradation and loss of hide of the proteins and too low temperature slow down the operation process. The safest temperature of liming is 20 degree at which the digestion of the skin or the leather making substance is very small. Under no circumstances should be temperature of liming be allowed to exceed 20 - 25 degree.
3. Float: 250 - 300 percent.
4. Time: Owing to the relatively high temperature and humidity close to saturation in the sweating chamber bacterial action takes place and hair is found to be loosened after about 48 hours. In practice, it usually take 18 - 48 hours.
5. Mechanical Agitation ( r.p.m): Mechanical agitation in drums or paddles will help in quicker liming but not too much ( 3 r.p.m).

Chemicals and auxilaries used in Liming process

1. Sodium Hydrosulphide: It is usually called sodium sulph-hydrate and it's molecular formula is NaSH. It is used as unhairing action.
2. Calcium Hydrosulphide: It has also unhairing action like sodium hydrosulphide. It's molecular formula is Ca(HS)2. It can be used for sharpening lime.
3. Arsenic Sulphide: There are two varieties of arsenic sulphide. They are red and yellow. The chemical formuka of former is As2S2 and the latter is As2S3 called respectively regular and orpiment.
4. Dimethyl Amine: It had pronounced unhairing action when add fresh lime liguor and they could use as sharpening agent.
5. Lime: It is a common commercial product, manufactured from limestone, chalk on a large scale. It is classified into two parts   1.Quick lime                 2. Slacked lime

 1.Quick lime: Lime is obtained by burning limestone, chalk or shell are described above is called quick lime (CaO). Quick lime is sold in commerce and is often used in tanneries after slaking.
 2. Slacked lime: Quick lime CaO, reacts vigorously with water 

CaO + H2O = Ca(OH)2

The product Ca(OH)2 chemically called Ca(OH)2 and it is commonly known as slacked lime.

Among these lime the sodium sulphide, sodium sulph-hydrate are commonly used.