THE COLLOID-CHEMISTRY OF SOAP MANUFACTURE 195 



molar concentration sodium carbonate is least effective, sodium 

 silicate takes a middle position and sodium borate is strongest. 

 The photographs (and the experimental protocols) show how, as 

 these different salts are used, the gelation point is shifted further 

 toward the left. It will be noted that sodium borate at half the 

 concentration of sodium silicate produces an equal degree of soap 

 filling and, also, that the sodium borate is as powerful in ultimate 

 effects as double the concentration of magnesium sulphate. 1 

 It is questionable, of course, whether the addition of magnesium 

 sulphate to soap has any justification whatsoever save that of 

 giving " load." Magnesium sulphate adds nothing to water which 

 improves its washing characteristics and, as the lowermost series 

 of tul>es in Figs. 96 and 97 show, it also partially decomposes 

 the sodium or potassium soap into the poorer magnesium soap. 



It will be observed in comparing the two figures that there is 

 a shifting of the gelation point toward the left as a sodium soap 

 takes the place of an equally concentrated potassium soap. This 

 is again identical with the similar shift observed in all the " salting- 

 out " experiments previously described. 



Ordinarily, in the manufacture of the filled soaps, the addition 

 of water-glass, borax or other material is carried to the highest 

 point possible short of the " cracking " or " liquefying " of the 

 mixture, or the " salting-out " of the soap. This point is always, 

 obviously, somewhere on this side of the optimum gelation point. 

 When through can-less mixing or error in judgment the filling of 

 a soap is carried beyond this critical point (represented by tran- 

 sition from the system salt-water-in-hyd rated soap to that of 

 hyd rat ed-soap-in-salt -water) what is to be done? What must 

 be accomplished is the reversal in type of system through dilution of 

 the salt and increase in the absolute amount of soap in the system. 

 The proper n-ult is not obtainable, however, through mere 

 addition of more soap and water. One might think that it could 

 l>e obtained by heating and subsequently cooling the mixture. Imt. 

 the soap in the>e mixtures is near the "stringing" point and 



therefore dangemu- to heat; or the added compounds are of a 



type which will not stand boil inn; without suffering hydrolysis 

 and permanent decomposition. The best way to proceed is to 



'In such observations, obviously, lie interesting material farts covering 

 th matter of th- quantity of "hydration" suffered by different salts in 



volution 



