Soap-Making Manual / A Practical Handbook on the Raw Materials, Their Manipulation, Analysis and Control in the Modern Soap Plant.

by Edgar George Thomssen

FLOATING SOAP.

Floating soap occupies a position midway between laundry and toilet soap. Since it is not highly perfumed and a large piece of soap may be purchased for small cost, as is the case with laundry soap, it is readily adaptable to general household use. Floating soap differs from ordinary soap in having air crutched into it which causes the soap to float in water. This is often advantageous, especially as a bath soap, and undoubtedly the largest selling brand of soap on the American market today is a floating soap.

In the manufacture of floating soap a high proportion of cocoanut oil is necessary. A most suitable composition is one part cocoanut oil to one part of tallow. This is an expensive stock for the highest grade of soap and is usually cheapened by the use of cottonseed or various other liquid oils. Thus it is possible to obtain a floating soap from a kettle stocked with 30 per cent. cocoanut oil, 15 per cent. cottonseed oil and 55 per cent. tallow. With this quality of soap, however, there is a possibility of sweating and rancidity, and of the soap being too soft and being poor in color.

The process of manufacture is to boil the soap in an ordinary soap kettle, after which air is worked into the hot soap by a specially constructed crutcher, after which the soap is framed, slabbed, cut into cakes and pressed.

Concerning the boiling of the soap, the saponification must be carefully carried out, as the high proportion of cocoanut oil may cause a violent reaction in the kettle causing it to boil over.

The method of procedure is the same as for a settled soap up to the finishing. When the mass is finally settled after the finish, the soap should be more on the "open" side, and the object should be to get as long a piece of goods as possible.

Due to its high melting point, a much harder crust forms on the surface of a floating soap and in a greater proportion than on a settled soap during the settling. In a large kettle, in fact, it has been found impossible to break through this crust by the ordinary procedure to admit the skimmer pipe. Much of the success of the subsequent operations depends upon the completeness of the settling, and in order to overcome the difficulties occasioned by the formation of the crust everything possible should be done in the way of covering the kettle completely to enable this period of settling to continue as long as possible.

When the soap is finished it is run into a specially constructed U-shape crutcher, a Strunz crutcher is best adapted to this purpose, although a rapidly revolving upright screw crutcher has been found to give satisfaction upon a smaller scale, and a sufficient quantity of air beaten into the soap to make it light enough to float. Care must be taken not to run the crutcher too rapidly or the soap will be entirely too fobby. During this operation the mass of soap increases in bulk, and after it has been established how much air must be put into the soap to satisfy the requirements, this increase in bulk is a criterion to estimate when this process is completed.

It is of course understood that the longer the crutching continues the greater quantity of air is incorporated and the increase of volume must be established for a particular composition by sampling, cooling the sample rapidly and seeing if it floats in water. If the beating is continued too long an interval of time, the finished soap is too spongy and useless.

The temperature of the mass during crutching is most important. This must never exceed 158 degrees F. At 159 degrees F. the operation is not very successful, yet the thermometer may indicate 140 degrees F. without interfering with this operation. If, however, the temperature drops too low, trouble is liable to be met with, by the soap solidifying too quickly in the frames.

When the crutching is completed, the soap is allowed to drop into frames through the valve at the bottom of the crutcher and rapidly crutched by the hand in the frames to prevent large air spaces and then allowed to cool. It is an improvement to jolt the frames as they are drawn away as this tends to make the larger air bubbles float to the surface and thus reduce the quantity of waste. When the soap has cooled, the frame is stripped and the soap slabbed as usual. At this point a layer of considerable depth of spongy soap will be found to have formed. This of course must be cut away and returned to the kettle. The last few slabs are also often rejected, inasmuch as the weight of the soap above them has forced out so much of the air that the soap no longer floats. As a fair average it may be estimated that not more than 50 to 60 per cent. of the soap in the kettle will come out as finished cakes. the remaining 40 to 50 per cent. being constituted by the heavy crust in the kettle, the spongy tops, the bottom slabs and scrapings. This soap is of course reboiled and consequently not lost, but the actual cakes obtained are produced at a cost of practically double labor.

It is advisable to add a small quantity of soap blue color to the mass while crutching to neutralize the yellowish tint a floating soap is liable to have.

Some manufacturers add a percentage of carbonate of soda, about 3 per cent., to prevent the soap from shrinking. Floating soap may also be loaded with sodium silicate to the extent of about 5 per cent.