200 ANNUAL OF SCIENTIFIC DISCOVERY. 







1.32 specific gravity being the state in which it is sold. After prepar- 

 ing, by the usual process, a certain quantity of pure soap with tallow, 

 oil, or other kind of grease, and when the boiling is just finished, it is 

 poured, while still hot and in a fluid state, into forms or moulds, and 

 the desired quantity of concentrated solution of silicate of soda, either 

 cold or heated, is added at the same instant. To incorporate the sili- 

 cate thoroughly, the mass is stirred until the cooling renders this op- 

 eration difficult. It is then left to harden, By this process, the sili- 

 cate of soda becomes so perfectly incorporated with the soap that as 

 much as sixty per cent, of this solution at 35 B. may be added, and 

 yet yield a soap of adequate consistency. But generally not more 

 than from twenty-five to forty per cent, of silicate is added to the soap. 

 It is this power of adding so large a proportion of alkaline silicate, 

 thoroughly saturated with silica, which forms one of the great advan- 

 tages of the American process. 



Soap prepared by the American process differs materially from or- 

 dinary resin soap neither in appearance or action. It has passed sat- 

 isfactorily through the trial of a great demand, and appears to serve 

 perfectly well for all the uses to which ordinary soap is applied. The 

 American government has already bought large quantities of it for the 

 use of the army at a much lower price than was formerly given for 

 resinous soaps, and it has undergone all the tests exacted by its agents. 



It may also be remarked, that a mixture of silicate of soda and or- 

 dinary soap has been preferably used for some time in washing woollen 

 fabrics in one of the largest establishments of the United States. 



Silicate of soda is useful to soap-makers for several qualities not pos- 

 sessed by resin ; for instance, the addition of a large quantity of silicate 

 of soda imparts to the soap neither that disagreeable odor nor the glue- 

 iness which too great a proportion of resin communicates. It may be 

 introduced into soap in much larger proportions than resin without in 

 any way injuring the sale of the product. 



It is not probable that resin will ever resume its former importance 

 to the soap-maker. It will still be used conjointly with the silicate of 

 soda, since a little resin serves to correct the nauseating odors of in- 

 ferior fats, and because, according to some makers, it augments the 

 detersive action of the soap. 



The use of soluble glass in hard soaps should not be confounded with 

 the use, as detergents, of simple solutions of silicate of soda. The latter 

 are simply alkaline solutions, similar to those of alkaline carbonates. 

 They act chiefly, if not wholly, by their chemical nature, for they do 

 not lather, and in that and other respects are unlike real soaps ; while 

 the silicate of soda soap, owing to the portion of fatty acid it contains, 

 lathers abundantly, and behaves like ordinary soap, the mechanical 

 and chemical conditions required by a good soap being fulfilled. 



It should be borne in mind that silicate of soda soap is distinct from 

 siliciferous soaps formerly prepared by the mechanical addition of silica 

 or of sonic insoluble silicate, such as silicate of alumina, which is sim- 

 ply a useless adulteration, while in soaps containing soluble glass a 

 portion of fatty acid, so to speak, is replaced by a weak, mineral acid, 

 equally efficacious in modifying the causticity of the alkali. 



The introduction of soluble glass for the manufacture of soap con- 

 stitutes another example of the rapidity with which one industrial pro- 



