1914
NOTI:
I n conclusion, I wish to acknowledge my indebtedness to the Director of these Laboratories, Professor hI. Rosanoff, under whose guidance the above study was carried out. CLARK UNIVERSITY.
WORCESTER,MASS., Julie, r9oS.
-
NOTE. On the “Color Demonstrat,ion of the Dissociuting Action of Wuter” 0 ) Jones and Allen.-Jones and 911en’ have published a well known lecture
demonstration of the “dissociating action of water,” Ivhich is rcpeatetl b ~ 7Jones in his text-book, ‘“l‘he Illemelits of I’hysical Chemistry.”’ ~ I A few drops of an alcoholic solution of phenolphthalein are placed in a glass cylinder, and diluted to, say, jo cc. b y the addition of alcohol. A few drops of a n aqueous solution of ammonia are then added. A red color may appear where the aqueous ammonia first comes in contact with the alcoholic phenolphthalein b u t this will disappear instantly on shaking the cylinder.. , . .\l.‘ater is then gradually added t o the cylinder, when the red color will appear, a t first faint then stronger as the aniount of water increases. LVlieti the red color has becorr;e intense, add :I considerat)le volume of alcohol, and the entire color vi.ill disappear.” This is given a s a demonstration of the dissociating action of water, the explanation being that in the alcoholic solution the atiinionia is so little dissociated t h a t there are not enough h!.drosyl ioiis present to color the phenol phthalein. Dilution with water dissociates the ammonia etiougli to give the red color t o the indicator. ’l‘lie further addition of alcohol represses the dissociation and the solution again becoines colorless. Recent light on the niechanism of the color change iri indicators, and a comparison of the relative dissociating power of alcohol with its enornioiis decolorizing power on slightl!. alkaline 1)lieiiolphthaleiii solutions made it seen1 highly improbable t h a t the reasoil for thc color change was the one assigned by Jones ;iml A l l l e ~ i .’I‘his property of alcoliol was noticed by the bvriter wtiile measuring the t1issociutic.m constant ol ~ ~ l i e n o l ~ ~ h t l i a l e i i i . ~ ~ 1t \vas first remarked by hlenscliutki~i~ arid further ol)servetl quantitatively I)! A I C C ‘ O ~ . ~ ’I‘he effect of the alcohol in this respect is so great as to preclude the possibility of its being due, except in \-er!. sniall proportion, to the smaller dissociating power of the ~ ~ l c o h o l .Solutiolis o f salts in :~lcoliol sho~v a degree of dissociation about one-tliirtl t l u t i i i Nistures of I
$:
5
6
:tnler. Ckctil. J , , 18,377 ( I X C ~ ( I ) . Third edition, 1907, 11. 2‘)s. %. Efekfrociiem., 14,352 (1cp8). 16, 3 1 5 (1883). A m r r . Cliem. J . , 31, 503 (1904). Jones, Z . physik. Chem., 14,jor (1894).
1915
NOTE.
alcohol and water as solvents show a decreased conductivity b u t the decrease is not great and even a large part of t h a t is due to the increased viscosity.' Even if, say, twenty-five per cent. of alcohol repressed the dissociation of the ammonia to half its former value, the equilibrium equations involved show t h a t we would expect the intensity of color of the indicator to be reduced one-half. As a matter of fact, under proper conditions this amount of alcohol is more than sufficient to decolorize the phenolphthalein completely. How then is the great color change to be accounted for? All the recent work on indicators gives evidence t h a t the color change is due not simply to a difference in color between the ion and undissociated molecule,2 b u t rather to an equilibrium between two differently colored tautomeric fornis, the amount of one varying according as the other is dissociated Hi B- if the first or I n the double equilibrium A HE equilibrium is mostly in the direction of ,4 and the dissociation constant of H B is small, then if H+ is large the indicator exists mostly as A having one color, if small, mostly as B- with a different color. Although the case with phenolphthalein is rather c ~ m p l i c a t e d let , ~ us assume for simplicity that A represents the colorless part, and B- the red ion. It is evident t h a t the color could be diminished not only by increasing 11' as Jones and Allen assume, b u t also by a combination of the alcohol with A. The solubility of phenolphthalein in alcohol renders this not improbable. Now if the addition of alcohol changes considerably the concentration of the hydrogen ion, then the color change should be shown by other indicators besides phenolphthalein. If, however, the color of other indicators is not correspondingly altered, then the change in this case must be due to a combination of alcohol with the colorless form of the phenolphthalein. Colorimetric measurements were made to compare phenolphthalein with other indicators in their behavior towards alcohol. To 15 cc. of a phenolphthalein solution partly dissociated with ammonia were added 2 cc. of neutral alcohol, and the change in color was noted, correcting for the dilution. The same procedure was carried out with litmus, paranitrophenol and rosolic acid. With litmus sodium light was used which gave the amount of blue in the presence of the red. U-ith rosolic acid, green light gave the red in the presence of the yellow. The varying color was produced by ammonia or acetic acid as the case might be. The dissociation constant of acetic acid being nearly the same as that of am-
+
Jones and Carroll, Amer. Chem. J . , 32, 521 (1904). Ostwald, Lehrb. d. allg. Chem., 2nd edit., Vol. I, p. 799, Stieglitz, /. Amer. Chem. SOC., 25, 1 1 1 2 (1903). Acree, Amer. Chem. J . , 39, 5 2 8 (1908).
1916
NE&' BOOKS.
nionia, any decrease in dissociation tluc to the alcohol \\oulcl be the same for both. e , 1he results are given in thc table. 'l'hc ligures for litmus are 011 the assumption t h a t it is an acid. Per cent. dissociation.
Indicator.
Before After addin 13 additig alcohol. per cent. alco%oi.
Phenolphthalein . . . . . . . . . . . . . . 1,itrnus.. . . . . . . . . . . . . . . . . . . "
.......................
(J;
j(t .{2
p-Nitrophenol . . . . . . . . . . . . . . . . X o (L . . . . . . . . . . . . . . . . 12 Rosolic acid . . . . . . . . . . . . . . . . . . . 57
,3
Decrease.
37 -4 - -3 --I
-4 0
I t will be seen t h a t phenolphthalein is alone in its behavior with alcohol, t h e latter even producing a slight i m x u J c in dissociation with litmus and p-nitro phenol. I t would seem, therefore, that the decrease in the dissociatioil of t h e ammonia plays but a \.cry small part in the decolorizatiori of phenolphthalein b y :ilcohol, atid that the "color demonstration " depends upon soniething quite dili'erent from that which its authors Joici. 1I . H I L D E I ~ I ~ A S I ~ . state.' U N I V E R S I T Y 01' P E N X S Y L V A N I A .
___ __._
NEW BOOKS. Text-book of Physiological Chemistry. By EMIL ADDI3RHALDEs. Translated b y \VII,siii + LIAM T. HALLand GEORGEDISFREN.S e w York: john Wiley and Sons. 7 2 2 pp. Price, $5.00 ne!.
One may almost take for granted t h a t a book by so versatile a n investigator as Professor Abderhalden will not be commonplace. This volume differs from those of his predecessors in the point of view taken towards the subject and tlie treatment accorded t o the topics selected for consideration. Indeed, the title "'rest book" seems somewhat niisleadiiig for a treatise of this character. 'i'he book is in 110 sense a catalogue of d a t a regarding the composition of animal and plant iluids and structures; and it cannot pretend t o include a n y rigidly systematic or uiiiforni chemical survey of elementary biological tissues. Such knowledge regarding the make-up of parts oi liviiig things merely furnishes the starting point to-day in ~'li\-siological-cheniical considerations. 'l'lie author maintains t h a t the problems o f nietabolisni have 1:ecome the (lomain of the physiological clieinist. ".I linal goal of research will be attained when we are able to follow iii every separate phase, each and eyer>- foodstun' from the timr of its introduction into t h r alimentary c:ind throughout its entire sta!. i l l the tissues until it is finally elinii1 'rliis paper \vas sulimittrd 111 I'rof. J ( I X I C S \Tho very coi-dially urgcd its pub1ic:itioii, saying that he :llsu was of til? o1)inion t h t t l l r crplanation offered by hfr. .k11en
and himself was nut sufficient.
