EMULSOIDS 



297 



shown by the arrows, the kations and the anions are arranged 

 in ascending order of precipitating and inhibiting power 

 respectively. The symbols + and - respectively signify that 

 the salt does or does not precipitate albumen, the blank spaces 

 meaning that the salt has not been investigated. 



Rations -> Mg NH^ K Na Li 



Anions. 



Fluoride + + + 



Sulphate + + + + + 



Phosphate + + + 



Citrate + + + 



Tartrate + + + 



Acetate + + 



Chloride + + + 



Nitrate + + 



Chlorate + 



Bromide - + 

 Iodide 

 Sulphocyanide - 



From this table it may be seen that the dbmparatively 

 slight precipitating power of the kations, Mg and NH 4 -, is 

 completely neutralized by the anions -C 2 H 3 O 2 or -Cl, while 

 the more powerfully inhibiting anions -NO 3 and -C1O 3 are 

 able to netralize the precipitating power of the kation K as 

 well as that of Mg and NH 4 -. Similarly the powerfully in- 

 hibiting anions -Br, -I and -CNS, are able to counteract the 

 precipitating power of sodium as well. 



SWELLING OF COLLOIDS OR IMBIBITION. 



Whereas a water soluble crystalloid commences to dissolve 

 as soon as it is brought in contact with water, the same is not 

 true for most emulsoid or lyophilic colloids. Before going into 

 solution, these substances undergo a preliminary swelling, some- 

 times known as imbibition ; this is accompanied by the dis- 

 appearance of a certain volume of water. According to an ex- 

 periment described by Hatschek, one gram of gum tragacanth 

 covered with water in a specific gravity bottle kept under 

 water for a week had increased in weight by 0-9 gram at the 

 end of this period ; this means that in the process of imbibi- 

 tion the gum had succeeded in drawing into the flask 0-9 c.c. 

 of water. In view of the resistance which water is known to 

 offer to compression, it is clear that enormous force must have 

 been exerted during the process. 



Direct measurement of the pressures produced during 



