THE COLLOID-CHEMISTRY OF SOAPS 31 



(which are readily reproducible) in the case of an actual experi- 

 ment, are shown in Figs. 14 and 15 and in Table X. The 

 findings detailed in Table X are shown graphically in Fig. 16. 



A sodium oleate-ethyl alcohol gel prepared under identical 

 conditions is pictured in Fig. 17. 



It is again of interest to note in connection with these experi- 

 ments in which ethyl alcohol is used that, with the exception of 

 margaric acid (about which there is still a debate as to whether 

 or not it is more than a eutectic mixture of palmitic and stearic 

 acids) all the soaps which show distinctly lyophilic properties 

 are those of acids which have an even number of carbon atoms in 

 the empiric formula. This fact was formerly emphasized in tlu 

 case of these soaps, when water was the " solvent " concerned. 



The tendency to yield colloid gels diminishes not only quanti- 

 tatively but also qualitatively, as we descend the fatty acid series 

 from sodium arachidate to sodium acetate. The ethyl alcohol 

 gel of sodium acetate tends to crystallize out within a few days 

 after its formation. The butyrate gel (see Fig. 14) may go partly 

 to pieces in the course of weeks, unless carefully proUvted fmm 

 temperature changes, but the caproate yields a lasting colloid. 

 These lowermost members of the soap series with an even number 

 of carbon atoms, however, show a clean-cut tendency to gel 

 formation not at all apparent with the formate, propionate and 

 valerate. In the case of the last named substances, repeated 

 trials under the conditions of our experiments yielded only thick 

 crystalline precipitates. 



It is further to be noted (Fig. 16) that the regular downward 

 gradation in gelation capacity Ls interrupted in tin* series between 

 capric and caprylic acids. This point mark< tin- tran.-ition 

 the fatty acids solid at ordinary temperatures, to those which 

 are liquid. 



2. It was our next problem to discover what was the {fetation 

 capacity of some picked soaps in different alcohol*. We used for 

 this purpose several sodium soaps of the arctic acid series, thni* 

 sodium soaps of the oleic .- I one sodium soap of the linolir 



series. 1 The emcate and linolate were prepared through IM-U- 



1 The matter of getting abw>lut< Iv |>u id* for foeh quantitative 



We at* under great 



-\JM -riini -Mta as are here described is not an e**y one. We at* under great 



oMmttion to the Depart in. m ,,f Organic Manufacture 



III..,.,.- f,, r MprtjrfcM u< w.ili -pl.-iHlid example* of the diffrrrnt 



used in this study. In anoth. r j-.rtion of the work we lined KahJtum> K 



