768 SOAP.—Saponification.

no longer gives off carbonic acid on being treated

divest carbonate of lime of a portion of its carbonic

with hydrochloric acid. The lye thus made contains

acid.

less lime than that made in the cold. When the

Of late years caustic soda for soap-making has

calcium carbonate has entirely subsided the liquor is

been manufactured to a very considerable extent by

drawn off into tanks. The residual precipitate is

alkali - makers, and the trade is likely to be greatly

washed with water, and the weak liquor is used for

increased; and it is evident that its employ-

diluting stronger lyes, or in place of water for the

ment would be much more economical to the soap

next caustieizing operation.

manufacturers than the present method of pre-

A fact deserving of mention in treating of the

paration. The caustic soda requires simply to be dis-

preparation of lyes is, that in the process of caustic’z-

solved in a given quantity of water to produce lyes

ing by means of lime, a portion of the soda appears to

ready for use and of any required strength.

enter into some form of combination very difficultly

Testing the Lye . —For this purpose specific gravity

soluble. Ivynaston found the residue to contain, after

bulbs, or the hydrometer, is used. In this country

being well washed, soda to the amount of 5 or 6 per

Twaddell’s hydrometer is most commonly em-

cent. When the deposit, after being dried, is heated

ployed. The degree indicated by Twaddell’s

to a temperature insufficient to expel carbonic acid,

hydrometer, multiplied by 5 and added to 1000, ex-

and after being allowed to cool is again drenched

presses the specific gravity of the fluid. A lye test-

with water, caustic soda is then removed with great

ing 27'50 Twaddell, for instance, has a density equal

ease, and the deposit may be almost completely

to 1T38, which is equivalent to 15 per cent, of pot-

deprived of soda. Taking these facts into con-

ash or 12 - 8 per cent, of soda, always supposing the

sideration, it is very probable that it would well

lye to contain no other matters or salts which might

repay the soap manufacturer to collect the lime

also affect the specific gravity. This, however, is

deposit, and after thorough desiccation by exposure

never the case with soap-boilers’ lye, so that the

to the air, to submit it to heat until the carbonic

indications are only approximations with reference

acid is expelled. The lime now again become

to the amount of alkali, or even may be altogether

caustic may be used advantageously in the prepar-

fallacious. Still they are useful in a variety of ways,

ation of fresh lye, and the process may be repeated

and are indeed indispensable. The practitioner is

until the deposit becomes highly charged with the

able with this instrument to follow the diminishing

impurities of the ash, when fresh lime may again beused for a new process.

The addition of alum to soda lyes is stated byKottula to facilitate saponification. The lyes aremade hot, and the alum added in the following pro-portions :—

strength of the liquid flowing from the ash tubs orvats, and to form a just estimate of its value, when,at the same time, a test with acid proves the absenceof carbonic acid. But even in the process of soap-boiling itself, the test of the lye afforded by thehydrometer, combined with the personal experienceof the workman, is a clue by which he is enabled to

12 ozs. 10° B.

judge whether the proper strength has been attained;

18 ozs. 15° B.

knowing as he does what degree the hydrometer

24 ozs . 20° B.

30 ozs . 25° B.

ought to indicate from any particular soda or potashlye for any particular purpose. The more or less

Another of those progressive steps manufacturers

caustic taste of a lye is also a test much depended on

frequently take, leading to the simplification of

by many soap-boilers.

operations which previously had been tedious, labo-

Saponification.—O ils and fats themselves are

rious, and wasteful, has been taken in the soda trade,

neither soluble in water nor miscible with it, but

the especial benefits of which are to be derived par-

nearly all are made so by union with alkali. The

ticularly by the soap-maker and the public generally.

process of effecting this combination is termed

This intellectual advancement consists in preparing

saponification, and the compound produced is soap —•

directly the caustic alkali, by the use of which the

hard soap when its base is soda, but a more or less

soap-maker at once dispenses with a considerable

soft soap when potash is the alkali present.

"

plant outlay, economizes space, expedites the oper-

The properties and composition of oils and fats

ations of his trade, and effects no little amount of

have already been described. It is sufficient to state

saving in labour alone, compared with the presentgeneral practice. Besides the foregoing immediateand apparent advantages resulting in favour of thesoap-maker from the employment of caustic sodaprepared directly, there are others of much greaterimportance—namely, the economy of alkali, and thereadiness with which soap can be made by the useof lyes, the strengths of which are immediately undercontrol, and which cannot be obtained economicallyon the present cau-sticizing system to which soda

here that neutral fats, such as tallow, palm oil,cocoa-nut oil, &c., are the glyceryl salts of the fatacids; and their conversion into soap or “saponifi-cation ” consists in the separation of the glyceryland the acid, and results in the formation of analkaline salt of the fat acid (i.e., a soap) and glyce-rin, thus—■

- Stearins. <**»»«-•

(( (i$5 0)8 } 0 » + |}°3 = (< 2? J }°» +

ash is submitted, unless at considerable trouble;

Potassium Stearate.

and even then the lyes are not pure, owing to thecircumstance that strong caustic alkaline solutions

3 Atoms.

.