The grades are as follows:--

W. W. (Water white.) W. G. (Window gla.s.s.) N. (Extra pale.) M. (Pale.) K. (Low pale.) I. (Good No. 1.) H. (No. 1.) G. (Low No. 1.) F. (Good No. 2.) E. (No. 2.) D. (Good strain.) C. (Strain.) B. (Common strain.) A. (Common.)

Unsaponifiable matter is present in rosin in varying amounts.

Below are a few typical figures taken from a large number of collated determinations:--

________________________________________________________________ | | | | | | | | Saponification | Total | Free | Iodine | | | Equivalent. | Acid No. | Acid No. | No. | |________________|________________|__________|__________|________| | | | | | | | American W. W. | 330.5 | 169.7 | 119.1 | 126.9 | | American N. | 312.3 | 179.6 | 161.4 | 137.8 | | French | 320.5 | 175 | 168 | 120.7 | | Spanish | 313.4 | 179 | 160 | 129.8 | |________________|________________|__________|__________|________|

ALKALI (CAUSTIC AND CARBONATED).

The manufacture of alkali was at one time carried on in conjunction with soap-making, but of late years it has become more general for the soap manufacturer to buy his caustic soda or carbonated alkali from the alkali-maker.

Although there are some alkali-makers who invoice caustic soda and soda ash in terms of actual percentage of sodium oxide (Na_{2}O), it is the trade custom to buy and sell on what is known as the English degree, which is about 1 per cent. higher than this.

The English degree is a survival of the time when the atomic weight of sodium was believed to be twenty-four instead of twenty-three, and, since the error on 76 per cent. Na_{2}O due to this amounts to about 1 per cent., may be obtained by adding this figure to the sodium oxide really present.

_Caustic soda_ (sodium hydrate) comes into commerce in a liquid form as 90 Tw. (and even as high as 106 Tw.), and other degrees of dilution, and also in a solid form in various grades as 60, 70, 76-77, 77-78.

These degrees represent the percentage of sodium oxide (Na_{2}O) present plus the 1 per cent. The highest grade, containing as it does more available caustic soda and less impurities, is much more advantageous in use.

_Carbonate of soda_ or _soda ash_, 58, also termed "light ash," and "refined alkali". This is a commercially pure sodium carbonate containing about 0.5 per cent. salt (NaCl). The 58 represents the English degrees and corresponds to 99 per cent. sodium carbonate (Na_{2}CO_{3}).

_Soda ash_, 48, sometimes called "caustic soda ash," often contains besides carbonate of soda, 4 per cent. caustic soda (sodium hydrate), and 10 per cent. salt (sodium chloride), together with water and impurities.

The 48 degrees refers to the amount of alkali present in terms of sodium oxide (Na_{2}O), but expressed as English degrees.

_Caustic potash_ (pota.s.sium hydrate) is offered as a liquid of 50-52 B.

(98-103 Tw.) strength, and also in solid form as 75-80 and 88-92. The degrees in the latter case refer to the percentage of pota.s.sium hydrate (KHO) actually present.

_Carbonate of Potash._--The standard for refined carbonate of potash is 90-92 per cent. of actual pota.s.sium carbonate (K_{2}CO_{3}) present, although it can be obtained testing 95-98 per cent.

OTHER MATERIALS.

_Water._--Water intended for use in soap-making should be as soft as possible. If the water supply is hard, it should be treated chemically; the softening agents may be lime and soda ash together, soda ash alone, or caustic soda. There are many excellent plants in vogue for water softening, which are based on similar principles and merely vary in mechanical arrangement. The advantages accruing from the softening of hard water intended for steam-raising are sufficiently established and need not be detailed here.

_Salt_ (sodium chloride or common salt, NaCl) is a very important material to the soap-maker, and is obtainable in a very pure state.

Brine, or a saturated solution of salt, is very convenient in soap-making, and, if the salt used is pure, will contain 26.4 per cent.

sodium chloride and have a density of 41.6 Tw. (24.8 B.).

The presence of sulphates alters the density, and of course the sodium chloride content.

Salt produced during the recovery of glycerine from the spent lyes often contains sulphates, and the density of the brine made from this salt ranges higher than 42 Tw. (25 B.).

_Soapstock._--This substance is largely imported from America, where it is produced from the dark-coloured residue, termed mucilage, obtained from the refining of crude cotton-seed oil. Mucilage consists of cotton-seed oil soap, together with the colouring and resinous principles separated during the treatment of the crude oil. The colouring matter is removed by boiling the mucilage with water and graining well with salt; this treatment is repeated several times until the product is free from excess of colour, when it is converted into soap and a nigre settled out from it.

Soapstock is sold on a fatty acid basis; the colour is variable.

FOOTNOTES:

[1] Calculated by us from saponification value.

[2] Calculated by us from saponification value.

[3] Calculated by us from saponification value.

[4] Calculated by us from saponification value.

[5] Calculated by us from saponification value.

[6] Calculated by us from saponification value.

[7] Calculated by us from saponification value.

[8] Calculated by us from saponification value.

[9] Calculated by us from saponification value.

[10] Calculated by us from saponification value.

[11] Calculated by us from saponification value.

[12] Calculated by us from saponification value.

CHAPTER IV.

BLEACHING AND TREATMENT OF RAW MATERIALS INTENDED FOR SOAP-MAKING.

_Palm Oil--Cotton-seed Oil--Cotton-seed "Foots"--Vegetable Oils--Animal Fats--Bone Fat--Rosin._

Having described the most important and interesting oils and fats used or suggested for use in the manufacture of soap, let us now consider briefly the methods of bleaching and treating the raw materials, prior to their transference to the soap-pan.

_Crude Palm Oil._--Of the various methods suggested for bleaching palm oil, the bichromate process originated by Watts is undoubtedly the best.

The reaction may be expressed by the following equation, though in practice it is necessary to use twice the amount of acid required by theory:--

K_{2}Cr_{2}O_{7} + 14HCl = 2KCl + Cr_{2}Cl_{6} + 7H_{2}O + 6Cl.

6Cl + 3H_{2}O = 6HCl + 3O.

The palm oil, freed from solid impurities by melting and subsidence, is placed in the bleaching tank, and washed with water containing a little hydrochloric acid. Having allowed it to rest, and drawn off the liquor and sediment (chiefly sand), the palm oil is ready for treatment with the bleaching reagent, which consists of pota.s.sium bichromate and commercial muriatic acid. For every ton of oil, 22 to 28 lb. pota.s.sium bichromate and 45 to 60 lb. acid will be found sufficient to produce a good bleached oil.

The best procedure is to act upon the colouring matter of the oil three successive times, using in the first two treatments one-third of the average of the figures just given, and in the final treatment an appropriate quant.i.ty which can be easily gauged by the appearance of a cooled sample of the oil.