ise. Palmitin exists in scales,
which have a peculiar pearly appearance, and are greasy to the touch.
After melting and solidifying, palmitin shows no crystalline fracture;
when heated to 46 deg. C. it melts to a liquid which becomes solid on
further heating, again liquefying when 61.7 deg. C. is reached, and becoming
cloudy, with separation of crystalline particles. At 63 deg. C. it is quite
clear, and this temperature is taken as the true melting point. It has
been suggested that the different changes at the temperatures mentioned
are due to varying manipulation, such as rate at which the temperature
is raised, and the initial temperature of the mass when previously cool.

_Olein_ (Triolein) is an odourless, colourless, tasteless oil, which
rapidly absorbs oxygen and becomes rancid. It has been prepared
synthetically by heating glycerol and oleic acid together, and may be
obtained by submitting olive oil to a low temperature for several days,
when the liquid portion may be further deprived of any traces of stearin
and palmitin by dissolving in alcohol. Olein may be distilled _in vacuo_
without decomposition taking place.

_Laurin_ (Trilaurin) may be prepared synthetically from glycerol and
lauric acid. It crystallises in needles, melting at 45 deg.-46 deg. C., which
are readily soluble in ether, but only slightly so in cold absolute
alcohol. Scheij gives its specific gravity, _d_60 deg./4 deg. = 0.8944. Laurin
is the chief constituent of palm-kernel oil, and also one of the
principal components of cocoa-nut oil.

_Fatty Acids._--When a fat or oil is saponified with soda or potash, the
resulting soap dissolved in hot water, and sufficient dilute sulphuric
acid added to decompose the soap, an oily layer gradually rises to the
surface of the liquid, which, after clarifying by warming and washing
free from mineral acid, is soluble in alcohol and reddens blue litmus
paper. This oily layer consists of the "fatty acids" or rather those
insoluble in water, acids like acetic, propionic, butyric, caproic,
caprylic and capric, which are all more or less readily soluble in
water, remaining for the most part dissolved in the aqueous portion. All
the acids naturally present in oils and fats, whether free or combined,
are monobasic in character, that is to say, contain only one
carboxyl--CO.OH group. The more important fatty acids may be classified
according to their chemical constitution into five homologous series,
having the ge