Saturday, July 16, 2011

OXY ACIDS (PETROL INSOLUBLE ACIDS)

          Prepare the total fatty acids extract with petroleum ether (B.P.40 to 60 deg.C.) under reflux dissolve the residue in alcohol, evaporate to dryness and weigh . The term oxy acids is a very vague one and merely indicates the substances which are insoluble in petrol ether but solely in alcohol. Amongst these bodies is dihydroxystearic acid and consequently a high percentage of oxy acids does not necessarily indicate that it has oxidised at the double bond by addition of the OH group probably due to decomposition of peroxides .
However when a typical case of undesirable oxidation of an oil on wool is examined it is invariably found that the paint like sub stances present are insoluble in petroleum ether but soluble in alcohol.

WETTING OUT AND LATHERING POWER
         When the surface tension of a pure liquid is lowered by solution in it of any substance this substance concentrates in the surface to form a specially concentrated layer and the nature of this layer determines the lathering power. Wetting out is mainly a function of surface tension the deciding factor in the wetting of a solid by a liquid being the interracial tension liquid solid .
The angle at which a liquid joins a solid which it does not wet is termed the contact angle , this becomes less as the interracial tension in lowered until at complete wetting it is zero .The contact angle decreases as the relative humid ity increases a point of practical importance A low interracial tension confers on the wetting liquid the power of penetrating into capillary channels and interstices of textile materials. The surface tension of wetting and detergent solutions is decreased with increase of temperature . The soaps from liquid fatty acids such as oleic are better foaming and emulsify more readily than soaps from solid fatty acid such as Stearns acid at low temperatures , but the reverse is the case at boiling point Foaming is a general indication of wetting power though it is more reliably a measure of emulsion formation.