January 4, 1918] 



SCIENCE 



13 



Ostwald defines peptization as the plienom- presence of neutral electrolyte (much more so 



enon opposed to coagulation. than colloidal gold or platinum), while it is ir- 



Taylor prefers a new term, "solation," reversible when evaporated to dryness. Most 



which he applies to all cases of gel -> sol writers classify it with the suspensoids, 



transformations, and incidentally he urges the although Taylor calls it an emulsoid (since 



adoption of " gelation " to define all eases of if it be evaporated not quite to dryness it is 



Bol-»gel transformations instead of coagula- partially reversible). In reality it belongs to 



tion or pectization. ,^ , , neither of these two generally accepted classes ; 



Pectization, another of Graham s terms, ;+„ „, »■ i -^ -j i. ^ ^i, ^ 



.„ , . _,, , „ ' its properties place it midway between the two, 

 is rapidly dying out. The word "coagula- ., -j ^i. ^i i -j i 

 ,. ,, „ . . . , f nearer the suspensoid than the emulsoid class, 

 tion " covers all cases of pectization and there- a,i ^i i i -i ^ , , • 

 J. , ^ T-i -^ii the hydrous oxides of the basic or acidic 

 tore why preserve an unnecessary term s x ur- , ^ ... , , . . 

 ., 1. J i ^1 X i£ 1 X- » elements act similar to hydrous ferric oxide, 

 thermore, why adopt the new term " gelation _ j. i • \. 

 proposed by Taylor. "Coagulation" is ade- . On account of this confusion of classifica- 

 quate. Of course, if it is decided to name *'^^ Bancroft^i has suggested that the dis- 

 jellies (stiffened sols) "gels," then the word tinction between these two groups be done 

 " gelation " would be a good one to describe ^"^^^ ^^^^^ ^^ P'^'^^ers to classify colloidal 

 the " setting " of the gel or tlie stiffening of systems according as to whether water or the 

 the sol. more mobile phase, is the internal or the ex- 

 Elimination of some synonymous terms is ternal phase and states: "While we are rea- 

 decidedly necessary from the list of names sonably sure that colloidal gold is a solid and 

 applied to the two more or less distinct classes that colloidal oil is a liquid, the two behave 

 or systems of colloid dispersions. For ex- exactly alike when both are suspended electri- 

 ample, these two systems are variously named cally." 

 as follows: This suggestion is along the proper lines, 



Autbora 



Noyesio Colloidal solutions Colloidal suspensions 



Hardy,ii Zsigniondyis Reversible colloids Irreversible colloids 



Billitzeri3 Baser colloids Typical or genuine colloids 



? Hydrophilous colloids Anhydrophilous colloids 



Henrii* Stable colloids Unstable colloids 



Perrin, Freundlich,''' Neumann"'' Lyophilie colloids Lyophobie colloids 



Baryi' Dissolving colloids Electrical colloids 



Wo. Ostwaldis Emulsion colloids Suspension colloids 



von Weimarnio Emulsoids Suspensoids 



Burtonzo Gelatinizing type Non-gelatinizing type 



The terms " emulsoid ' ' and " suspensoid " but is too sweeping, since colloidal gold and 

 are very i)opular. " Lyophilie " and " lyo- colloidal oil do not behave alike. 

 phobic " are very expressive. The " stable- After a consideration of all the terms, it 

 unstable" and the "reversible-irreversible" would seem that " lyophilie " and " lyophobie," 

 terms should be abolished, since they describe or their more special derivatives, " hydro- 

 the conduct and changes in state of colloids phobic " are the least objectionable terms, 

 when subjected to external conditions and are since most colloids answer to one of these 

 not always sharply defined. For example, designations. When our knowledge of col- 

 hydrous ferric oxide sol is fairly stable in the loids becomes exact enough to sharply differ- 



10 J. Am. Chem. Soc, 27, 85 (1905). ^^Koll. Z., 3, 80 (1908). 



11 Proc. JRoy. Soc, 66, 95 (1900). "J. Chim. Phys., 10, 437 (1912). 



12 "Kolloidchemie. " is "Handbook of Colloid Chemistry." 



13 Z. physik. Chem., 45, 307 (1903). ""Grundziige der Dispersoidchemie. " 



i*Z. physik. Chem., 51, 29 (1905). so "Physical Properties of Colloidal Solutions." 



15 " KapUlarchemie. " ' 21 J. P/ij*. C/iem., 18, 549-558 (1914). 



