THE NEW YORK JOURNAL OF PHARMACY 



11 



Fats, fatty acids, albumen and its de- 

 composition-products, decrease the sur- 

 face tension of water very considerably 

 and are also readily adsorbed. It ap- 

 pears that adsorption is a physical phe- 

 nomenon anrl that no chemical process 

 plays any part. Ostwald, to emphasize 

 this, has termed it '"Mechanical adsorp- 

 tion." 



(ii) Reactions in jellies: When we 

 allow chemical reactions to take place in 

 jellies, we find that the reaction-product 

 separates out in ring forms, which rings 

 appear in periods. A gelatine "gel" con- 

 taining j)Otassium dichromate, with a sol- 

 ution of silver nitrate on top of it, will 

 slowly show the yellow rings of silver 

 chromate. Such rings are called "Liese- 

 gangs rings" after the scientist who in- 

 vestigated them most thoroughly. 



On reviewing what I have told you so 

 far about the preparation and properties 

 of colloids, I find that I have omitted 

 much that is important and exceedingly 

 interesting, but I must hurry. I hope, 

 however, that another opportunity will 

 present itself to take some one certain 

 phase of colloid-chemistry and go into it 

 more thoroughly. Time docs not permit 

 me to tell you anything about the meth- 

 ods of colloid research, ^lost of them are 

 directed, of course, by the properties of 

 colloids. Splendid and very promising 

 results have been obtained by the method 

 of ultra-filtration devised by Rechold. In 

 fact, colloid chemistry has opened a field 

 of research which is tremendousl\- large. 



There is no science in which colloid 

 chemistry does not enter in some way or 

 other, and as a system of knowledge it 

 is of the utmost importance. Each of 

 us here is a fine example of heterogene- 

 ous polyphasic colloid system; so is the 



chair on which you sit, the nails which 

 hold the pieces of wood together and the 

 glue which lends stability. You arise in 

 the morning — the linen of your bedding, 

 the feathers of your pillows are colloids, 

 you proceed to bathe and use soap — 

 again a cplloidal process. You have 

 your breakfast which consist of colloids; 

 digestion sets in — again a colloidal pro- 

 cess ; the cigar you smoke and the smoke 

 you exhale are colloidal systems — and so 

 on and on. To still more emphasize the 

 importance of colloids, I beg leave to 

 sav a few words about their uses in the 

 various arts and sciences. 



Cookery and Foods: The kitchen is 

 a great colloidal-chemical laboratory. 

 Meat of young animals is richer in juice 

 and of softer tissue than that of older 

 animals. This depends upon the swell- 

 ing value of the tissues, which value 

 changes with the age. Meat, on boiling, 

 loses 20-30 per cent, of its weight of 

 water — no doubt a dehydration of a col- 

 loid. On frying meat a heat coagulation 

 prevents the loss of juice. Artificial 

 foods are now classed according to their 

 content of carbohydrates and nitrogen. 

 The colloid chemist will classify them 

 according to their swelling value upon 

 which depends primarily the degree to 

 which a food can be readily absorbed. 

 Milk will be examined as to its surface 

 tension and viscosity which show abnor- 

 mal fat and protein contents. Addition 

 of water is detected by coagulation with 

 calcium chloride and the refractometer ; 

 the amount of milk sugar is estimated by 

 the polari scope after removal of the milk 

 ' colloids with colloidal ferric hydroxide. 

 Cheese is albumen coUoidally dissolved 

 in milk ; the determination of the swell- 



