solution, using a neutral solution of
potassium chromate as indicator. The final reaction is more distinctly
observed if a little bicarbonate of soda is added to the solution.

Number of c.c. required x 0.00585 x 100 = per cent. of common salt,
NaCl.

Chlorides may also be estimated by Volhard's method, the aqueous extract
being rendered slightly acid with nitric acid, a measured volume of N/10
silver nitrate solution added, and the excess titrated back with N/10
ammonium thiocyanate solution, using iron alum as indicator.

_Silicates._--These are estimated by evaporating 50 c.c. of the filtered
extract from the incinerated soap, in a platinum dish with hydrochloric
acid twice to complete dryness, heating to 150 deg. C., adding hot water,
and filtering through a tared filter paper.

The residue is well washed, ignited, and weighed as SiO_{2}, and from
this silica is calculated the sodium silicate.

_Sulphates_ may be determined in the filtrate from the silica estimation
by precipitation with barium chloride solution, and weighing the barium
sulphate, after filtering, and burning, expressing the result in terms
of Na_{2}SO_{4} by the use of the factor 0.6094.

_Moisture._--This is simply estimated by taking a weighed portion in
small shavings in a tared dish, and drying in the oven at 105 deg. C. until
it ceases to lose weight. From the loss thus found is calculated the
moisture percentage.

_Free or Uncombined Fat._--This is usually determined by repeated
extraction of an aqueous solution of the soap with petroleum ether; the
ethereal solution, after washing with water to remove traces of soap, is
evaporated to dryness and the residue weighed.

A good method, which can be recommended for employment where many
determinations have to be performed, is to dissolve 10 grammes of soap
in 50 c.c. neutral alcohol and titrate to phenol-phthalein with N/1
acid. Add 3-5 drops HCl and boil to expel carbonic acid, neutralise with
alcoholic KOH solution and add exactly 10 c.c. in excess, boil for
fifteen minutes under a reflux condenser and titrate with N/1 acid. The
difference between this latter figure and the amount required for a
blank test with 10 c.c. alcoholic KOH, denotes the amount of alkali
absorbed by the uncombined fat.

_Examination of the fatty acids_ as a guide to the probable composition
of the soap:--

From the data obtained by estimating the "titre," iodine number, and
saponification equivalent of the mi