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THE NEW YORK JOURNAL OF PHARMACY 



number increases, they adhere to one 

 another and finally form a net-like struc- 

 ture. By varying the amount of the 

 gelatine, we get slightly different results, 

 but we find that jellies are sponge-like 

 colloidial structures filled with colloidal 

 solution. 



Salts, or acids, or bases — in short, elec- 

 trolytes, have great influence upon swell- 

 ing. 



Acids and alkalis increase swelling, as 

 do many neutral salts. Gelatine swells 

 more in the presence of ^Magnesium Ci- 

 trate than in water alone. Calcium 

 Chloride, Hydrochloric Acid and Sodium 

 Hydroxide increase the swelling capacity 

 very considerably. The cause for this 

 must be sought in the chemical nature 

 of these hydrophilous colloids. They are 

 probably amphoteric, that is they have 

 weak acid and alkali reaction at the same 

 time. By an addition of acid or bases, 

 they form more or less ionized salts, 

 which in turn cause a hydration, or a 

 taking up of water, with subsequent in- 

 crease in volume. R. Chiari, in Vienna, 

 found that he could distinguish between 

 distilled water and ordinary water, by 

 means of the degree of swelling of puri- 

 fied globulin, which he found to be very 

 sensitive to electrolytes. 



(8) Coagulation: When we boil a 

 solution or albumin, or add Ammonium 

 Sulphate, we coagulate the albumen. 

 Coagulation is an electrical phenomenon 

 conditioned by colloids of different elec- 

 tric charge or by electrolytes. The 

 amount of electrolytes must, however, 

 exceed certain minimum values. 



Gold or platinum "hydrosols" can be 

 coagulated by Ferric or Aluminum 

 hydroxide "hydrosols," provided the 

 amounts added are such as to exactly 



neutralize the electric charge of each 

 other. A i/io,ooo per cent, solution of 

 gelatine will coagulate a mastic emul- 

 sion if more is added the gelatine will 

 act as a protective colloid. 



(9) Pectization is the gradual reso- 

 lution of substances into the colloid con- 

 dition ; for example, when we treat sil- 

 ver or mercurous iodide with solutions 

 of potassium iodide of different 

 strengths, we will get a colloidal solution. 

 Szillard, of Paris, has made a large num- 

 ber of interesting experiments in which 

 he tried to prove that inorganic sub- 

 stances can act like albumens. 



(10) Adsorption: We are all familiar 

 with the property of charcoal to con- 

 dense large volumes of gases, or to take 

 coloring matter out of solutions ; the 

 various silicates, like fuller's earth, 

 kaolin, etc., can be used for the same 

 purpose. Gelatine and isinglass can also 

 be used for clarification or decoloration. 

 The analyst knows that the concentra- 

 tion of certain salts (vi? . lead), is re- 

 duced upon filtration mrough paper. 

 These phenomena are classed as adsorp- 

 tion phenomena and are due like many 

 other properties of colloids to their tre- 

 mendously large surface development. 

 A cubic centimetre of a substance re- 

 duced to colloidal dispersion has a total 

 surface of 600 square metres and the 

 surface forces of the colloids are, there-. 

 fore, very pronounced. Adsorption is 

 caused by a decrease in the surface ten- 

 sion of the solvent conditioned by the 

 dispersed substance, or a third substance 

 added. Quincke showed that a substance 

 which causes a decrease in surface ten- 

 sion of a colloidal solution, has a ten- 

 dency to travel to the dispersoid phase 

 and form a sort of covering around it. 



