SOAP.— Toilet Soaps.

783

400 lbs. of tallow are introduced into the soap-pan,together with 250 gallons of potash lye, of suchstrength that 1 gallon contains 6000 grains of realpotash. Heat is now applied to the pan, and as themixture approaches the boiling temperature, muchfroth appears, and to prevent boiling over it isbeaten down on the surface. Should it subsidequickly into a doughy-looking paste, it is an indica-tion that too strong a lye has been used. Its properappearance is that of a thin glue. There shouldnow be added about 42 gallons of a stronger lye,equivalent to 8700 grains of potash per gallon, andafter a short interval, an additional 42 gallons; andthus successively until nearly a total of 600 gallonshas been introduced. After properly boiling, tocomplete the saponification of the fats, soap will beobtained amounting in quantity to 6400 lbs., fromthe above proportions of materials.

American soft soap differs very little from thepreceding in its mode of manufacture; 200 lbs. ofoil saponified by 72 lbs. of potash in lyes of specificgravity 1T10 = 22° Twaddell, yielding 450 lbs. offinished soap.

Fish-oil soft soap has usually a dark-brown colour,and that made from refuse fat and oil a dirty-whiteshade. Soap made with colza oil is slightly bluish.When hempseed oil is used, the soap has a greenishcolour. The latter is by some consumers preferredto other kinds of soft soap; and hence ordinary softsoap made from fish oil is frequently tinged green byadding a small proportion of powdered indigo.

Soft soap is always of a pasty consistence, andeven if excessively boiled, does not harden, butbecomes scorched and dry. In this country it ischiefly used for fulling, and for the scouring andcleansing of woollen stuffs. Being possessed ofgreater solubility, and having a much more power-fully detergent action, it is also especially applicablefor scouring floors and wooden utensils. In Ger-many, Belgium, and Holland it is also used forwashing linen, which thereby acquires a most dis-agreeable odour of oil.

There are two qualities of soft soap in the market.They contain—

l.

2 .

Fat acids,.

. 50'0 .

. 40*0

Potash,.

. 11-5 .

. 9*5

Water,.

. 38-5 .

. 50-5

100-0

100-0

Soda Soft Soap. —In this soap part of the potashis replaced by soda. The product has the char-acteristics of soft soap, but contains more water.

The lyes must be free from salt, or obviously theproduct would be a hard soap ; or if in too small aquantity for this, a certain quantity of hard soapwould precipitate and render the soap turbid insteadof transparent.

The best proportion is 1 part of soda to 4 ofpotash lye. A mixture of 100 lbs. of oleic acid (orr ed oil), 50 lbs. of tallow, and 3750 lbs. of hemp-seed oil, makes a good fatty mixture for this soap.

The Savon vert of Belgium and Germany containsabout equal parts of potash and soda soaps.

Hard Soap from Soft. —When chloride of sodium isadded to soft or potash soap, decomposition ensues,the chlorine of the salt seizes the potassium of thesoap, producing chloride of potassium; and at thesame time the sodium takes the place of the potas-sium in the soap, and a hard or soda soap results.The proportions recommended by Pellistier andothers for the conversion of soft into hard soaps,by means of the above-mentioned decomposition,are 6 lbs. of salt to every 3 lbs. of oil; and thesolution of the salt in water is to be added insmall portions and gradually to the soap, thelatter being in a state of ebullition. The sodasoap produced separates quickly from the lye, andthe operation is terminated in the usual way. Thisprocess for producing hard soap is of great import-ance in those countries where soda is not to beprocured, as potash and its salts may be substitutedfor the latter in the process of saponification.

Toilet Soaps. —Scented Soaps, Little-pan Soaps .—These soaps are ordinarily made without boiling,saponification being effected by mechanical means;or they are prepared by remelting and clarifyingwhite or curd soap, and adding various perfumes,colours, &c. Most of these soaps are already de-scribed in the article Perfumery .

Cold Saponifcation. —The fat is melted at a lowtemperature, and filtered. A very strong lye is thengradually added (not less than 56° B.), and stirredwell in with a wooden crutch, the mixture beingheated, but not allowed to boil. When the stirrerdraws a distinct ring, the colouring matter and per-fume is added. The temperature must not be below104° Fahr., nor above 149° Fahr. The paste shouldbe united, homogeneous, and of some consistence.Pressed between the fingers, it should be unctuous,without being greasy. When it has reached thisstate, it is run into frames lined with linen, andclosed in with a wooden cover, and left for twelveto twenty-four hours, when saponification will becomplete. During saponification the temperaturerises spontaneously to about 176° Fahr. When thesoap is cool, it may be taken from the frames, cut,pressed, and dried ; 112 lbs. of lard require 56 lbs.of caustic soda lye of 56° B.

Hawes' Process. —The tallow or other fat is meltedat as low a degree of heat as possible, and thenmixed with the quantityof alkaline lye requisiteto convert it into soap.

The mixing is performedby mechanical means.

Ordinary soap boilers’ lyeis used, preference beinggiven to that made fromthe strongest and purestalkali. To each 100 lbs.of tallow are requiredabout 20 gallons of lyemade from strong alkali,and of specific gravity1T25 = 25° Tw. An ordinary boiling caldron may beused as the combining vessel, with the addition of a

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