The phenomenon therefore closely parallels that observed when anhydronium bases of the type of I11 are acidified or are treated with ethyl iodide to give the cyanines IV. The color of a base I11 is invariably
to be due to the fact that addition of a proton a t the appropriate point enables the intensity of resonance within the conjugated system to he considerably increased. A full discussion of the halochromism of V will shortly be published elsewhere. LESLIEG . S. BROOKER KODAK RESEARCH LABORATORIES ROCHESTER, NEW YORK Atomic Weight Unit
To the Editor: Considerable interest has been shown recently in the matter of a name for the atomic weight unit. There seems to be no need for coining a new word to he added deepened on adding ethyl iodide to give a cyanine IV to the already long list of new words which the unhappy and this is held t o be due to substitution of the rela- freshman chemistry student must assimilate. Brinkley in "Introductory General Chemistry" calls tively weakly resonating system IIIa cr IIIb by the intensely resonating system IVa c-t IVb (here the two this unit just what it is, "the Atomic Weight Unit." extreme states are actually identical), hut the amount The unit is then defined as a weight which is oneof the shift in absorption depends on the value of n in sixteenth of the weight of the oxygen atom. This the formulas [BROOKER, SPRAGUE, SMYTH,AND LEWIS, method of presentation seems to offer less difficulty to the beginning student than the method of presenting 3. Am. Chem. Sac., 62,1116 (1940)l. An even more closely related phenomenon is the atomic weights as ratio numbers based upon the halochromism of 2-fi-dimethylaminostyrylquinoline(V). standard value of sixteen for oxygen. The use of the term "Atomic Weight Unit" has a definite pedagogical advantage hut I can see no reason for the use of such terms as "pel," "crith," etc. WARDC. SUMFTER WESTERNKENTUCKY STATE TEACHERS COLLEGE BOWLING
GREEN.KENTUCKY
.. Surface-Active Agents
This base, which is yellow, is deepened to wine-red on acidification or on conversion to the methiodide VI. VI
Q
Here again there is substitution of a weakly resonating system Va t--, Vb for the more strongly resonating system VIa ++ VIb and the same three resonanceinhibiting factors given above for I also apply to V, while only one of these remains to restrict resonance in VI (factor 3), as was also the case with 11. To sum up, the deepening of color accompanying the acidification of a base such as I, 111, or V is considered
To the Editor: The classification of surface-active agents given by Professor Degering on page 102 of the March issue is quite interesting and useful. . However, in the discussion of this tabulation and the classification of various commercial surface-active agents there appear to he inadvertencies. Of the various types of agents, the most commonly used domestically is undoubtedly the A. 1 type (the common soaps), not the C. 1 type. The commercial products mentioned, Cue, Dreft, Drene, Irium, and Teel, are probably all of the B. 1 type, not of the C. 1 type. Dreft, Drene, and Irium are stated by the mannfacturers to be alkyl sulfates. (See Ind. Eng. Chem., 33, 16 (1941), and H. L. Cupples, "A List of Commercially Available Detergents, Wetting, Dispersing, and Emulsifying Agents," Booklet E-504, Division of Insecticide Investigations, U. S. Department of Agriculture.) The alkyl sulfates are easily distinguished from the alkyl sulfonates (C. 1 type) by their relative ease of hydrolysis on boiling in dilute hydrochloric acid. CHARLES M. BLAIR,JR. 512 ATALANTAAVENUE WEBSTBR GROVES, MISSOURI
