JuxE 27, 1919] 



SCIENCE 



615 



Anne S. Young, who retained the greater part 

 of the original text and made such changes 

 only as were necessary to bring it down to 

 date. In general the changes were made with 

 discrimination and the text shows an im- 

 provement. Astronomy, however, is not a 

 complete science, and changes and improve- 

 ments are continually being made. This is 

 especially true of the applications of astron- 

 omy to practical matters. In some eases there 

 have been marked improvements in the ideas 

 and methods of thirty years ago, and too rigid 

 an adherence to the original text on the part 

 of Miss Yoimg detracts from the general ex- 

 cellence of the revision. In the discussion of 

 the tides, for example, there has apparently 

 been no change, and the old theory of a world 

 tide, originating in the Pacific and Indian 

 Oceans, has been adhered to. No mention is 

 made of the new theory advanced by the 

 Coast and Geodetic Survey that the tides are 

 purely local phenomena ; that the tides of each 

 locality originate in and are confined to that 

 ocean basin of which the particular locality 

 is a part; that the tides of the North Atlantic 

 have no connection with those of the Pacific. 

 The " Lessons " are for beginners, the " Ele- 

 ments " for the more advanced students. Both 

 books are excellent and no better text-books 

 have yet appeared for these classes of students. 



Charles Lane Poor 



SPECIAL ARTICLES 



FURTHER STUDIES IN COLLOID CHEMISTRY 

 AND SOAP 



The following summarizes exjierimental 

 findings and theoretical deductions which con- 

 tinue studies reported in these pages last 

 year.^ 



I 



Our previous work had emphasized not only 

 how from pure soaps and water most typical 

 lyophilic colloid systems may be produced but 

 in what way the chemical constitution of the 

 soaps and variations in concentration, tem- 



i Martin H. Fischer and Marian O. Hooker, 

 "Ternary Systems and the Behavior of Proto- 

 plasm," Science, 48, 143, 1918. 



perature, presence of electrolytes and non- 

 electrolytes, etc., changes the physical prop- 

 erties of these colloid systems. Practically all 

 attempts to explain such changes are to-day 

 electrical in nature. Without denying that 

 electrical phenomena sometimes play a role, 

 our newer experiments show that it may be 

 very small or need not function at all. 



Typical lyophilic colloid syntems may be 

 made of pure soaps in the practical or com- 

 plete absence of all water. The pure soaps 

 yield such colloid systems with the various 

 absolute alcohols, benzene, toluene, chloroform, 

 carbon tetrachloride and ethyl ether. We feel 

 that our future definitions of lyophilic colloid 

 systems and the understanding of their proc- 

 esses of swelling, gelation, syneresis, reversi- 

 bility of sol and gel states, hysteresis, etc., 

 must be expressed in the broader terms of 

 mutual solubility. As the hope of getting aU 

 phenomena of " solution " reduced to electrical 

 terms seems remote, the hope of getting these 

 fundamental colloid chemical findings reduced 

 to a similar level seems equally remote. 



Of the list of effective " solvents," the alco- 

 hols have received most study. The solvation 

 capacity of the different soaps (as measured 

 by the maximum amount of alchohol that will 

 be taken up to yield a " dry " or non-syneretic 

 gel at ordinary temperatures) varies in the 

 case of absolute ethyl alcohol for molar equiv- 

 alents of the sodium soaps of the acetic series 

 of fatty acids from practically zero in the 

 lowermost member to over 27 liters per gram 

 molecule in the case of sodium arachidate. 

 WTien the solvation capacity of unit weights 

 of any one soap for different alcohols is com- 

 pared, it is found that this is different not 

 only as mon-, di- or triatomic alcohols are 

 used but different, also, for the different alco- 

 hols in any one of the series. For the mona- 

 tomic alcohols, for example, the solvation 

 capacity increases progressively and smoothly 

 as the position of the alcohol rises in the 

 series. A gram of sodium stearate will just 

 form a gel at room temperature, for example, 

 with 50 c.c. of methyl alcohol, but the same 

 amount of the same soap will form a gel with 

 over 132 c.c. of amyl alcohol. When sodium 

 oleate is the soap employed all the absolute 



