ength bichromate in the blank experiment. If it
requires more or less than this, then the amount of ferrous ammonium
sulphate solution which would require exactly 10 c.c. (corresponding to
0.01 gramme glycerine) is calculated, and the oxidised glycerine
solution run into this until oxidation is complete.

The formula for the calculation of the percentage of glycerol then
becomes:--

{0.25 -(250 x 0.01)}
Per cent. of glycerol = { ---------- } x 500,
{ n }

where n equals the number of c.c. of oxidised glycerine solution
required to oxidise the ferrous ammonium sulphate solution.

Example:--

In the blank experiment 20 c.c. ferrous ammonium sulphate solution
required 9.8 c.c. one-tenth strength bichromate solution, so that 20.4
c.c. ferrous solution would equal 10 c.c. bichromate.

20.4 c.c. ferrous solution required 27.8 c.c. of oxidised glycerine
solution before it ceased to give a blue coloration with potassium
ferricyanide.
{0.25 - (250 x 0.01)}
Therefore, per cent. of glycerol = { ------------} x 500
{ 27.8 }

= 80.04 per cent.

Other methods have been suggested for the preliminary purification,
_e.g._, silver oxide, silver carbonate and lead subacetate, and copper
sulphate and caustic potash, but the lead subacetate alone with care
gives satisfactory results.

Other determinations include those of specific gravity, alkalinity,
proportion of salts and chloride, and tests for metals, arsenic, sulphur
compounds, sugar, and fatty acids.

_Specific gravity_ is determined at 15 deg. C., and may be taken in specific
gravity bottle, or with a Westphal balance or hydrometer It usually
ranges from 1.3 to 1.31.

_Alkalinity_, which is usually sodium carbonate, and may be somewhat
considerable if the soap has been grained with caustic alkali, is
determined after dilution with water by titrating with N/2 acid, using
methyl orange as indicator.

_Salts._--These may be determined by gently incinerating 5-6 grammes of
the glycerine, extracting the carbonaceous mass with distilled water,
filtering, and evaporating the filtrate on the water bath. The dried
residue represents the salts in the weight taken.

_Chloride of sodium_ (common salt) may be estimated by dissolving the
total s