440 SMITH'S INTERMEDIATE CHEMISTRY 



and in Great Britain, and much of that made in other countries, 

 is of this kind. 



The qualities of soaps are varied by adding " fillers," such as 

 sodium carbonate, borax, or sodium silicate. Soap powders are 

 often made of ground soap mixed with sodium carbonate. Dyes 

 and perfumes are sometimes added to soaps. Air bubbles are 

 mixed with the soap, by beating, to give the floating varieties. 

 Soap for scouring contains fine sand. Transparent soaps are 

 made by dissolving the soap in alcohol, or by the addition of 

 glycerine or sugar. 



Chemical Properties of Soaps. The soaps, being sodium 

 salts, dissolve in water and have the usual properties of salts. Thus, 

 when an acid is added, double decomposition takes place: 



Na(C0 2 Ci 5 H 31 ) + HC1 -> Nad + H(CO 2 Ci 5 H 3 i) J, . 



sodium palmitate palmitic acid 



The acids, being insoluble, are thrown down as white precipitates. 

 When other salts are added, similar actions occur. Thus with 

 calcium chloride solution, calcium palmitate is formed, and being 

 insoluble, is precipitated: 



2Na(C0 2 Ci 5 H 3 i) + CaCl 2 - 2NaCl + Ca(C0 2 Ci 5 H 3 i) 2 1. 



This action is important in connection with " hardness " in water 

 (p. 389). 



Colloidal Suspension. We have seen (pp. 109, 400) that 

 starch can be suspended in water in such a fine state of division 

 that the liquid is transparent, and runs through a filter without 

 leaving any solid on the paper. Yet this " suspension " lacks 

 some of the characteristic properties of a solution. 



The simplest proof, that this is a case of imitation solution, and 

 not of true solution (molecular dispersion, p. 108), is obtained 

 by examining the liquid with the ultra-microscope. A converg- 



