LETTERS To the Editor: This is a plea to teachers, particularly of first year chemistry courses, and to authors not to compound the confusion of thermodynamic definitions and symbolism (such as that of bhe sign of the electrode potentials and the F and G free energy symbols) by defining work of
"a"-and "8"-amylose are X-ray crystal pattern identifications not generally used as chemical designations. Cereal starches are a mixture of two polysaccharides, amylose (linear or able to form a helix with complexing agents such as 1%)and amylopectin (branched on C-6 of certain glucose units in the backbone). Waxy maize and glutinous rice are more than 95% amylopectin. Cereal starches have between 22 and 28% amylose. Corn has been bred at Purdue which contains up to 70% amylose. Only the amylose component gives a hlue color with iodine. Amylopectin gives a reddish-brown color. Soluble starch is a degraded cereal starch. It is not pure amylose.
P,,,
pdv, and as + w (work 1":done m the system): "'1t should be emphasized that
expansion as w
Ah'
= -
q
many of our first year students will also be takmg, simultaneously, physics courses in which work is deand AE as q - w (work done by .. the system). Educationally and conceptually, AE = -
q
+ w and w = -
">,*
L-
pdv offer no advantages.
T m CITYCOLLEGE OF NEWYORK NEWYORK,N.Y. 10031
To the Editor: Students may find a confusing statement about starch indicator in iodimetric titrations in two books.' The usual indicator for these titrations is a colloidal dispersion of starch, which, in the presence of iodide ions, gives a deep hlue color with even minute amounts of free iodine. Brown and Sallee state: "the so-called Lsoluhle starch' is principally 8-amylose and gives the blue coloration with iodine, a-amylose or amylopectin forms a red coloration with iodine . . . ." While Blaedel and Meloche write: "actually, one component (a-amylose) of ordinary starch gives the blue color with iodine. This component is available as soluble starch, which dissolves readily in water . 8-amylose forms a reddish color with iodine." Which statement should students and teachers accept?
To the Editor: I appreciated the recent article, "The Solvated Electron-the Simplest Ion and Reagent," by S. R. Logan (J. CHEM.EDUC., 44, 344, (1967)); however, I would like to suggest one addition or correction. Figure 1, "Absorption hand due to the hydrated electron in irradiated aqueous solutions, curves a and b," from HART,E. J., AND BOAG,J. W., (J. Am. Chem. Soc., 84, 4090; Nature, 197, 47 (1963)), (KEENE, J. P., Nature, 197, 45 (1963) gives a slightly different curve but also with ripples) is unnecessarily misleading. The references cited do indeed give spectra as indicated, hut since that time numerous investigations have shown the absorption spectrum of the hydrated electron to be a smoothly continuous single broad peak very similar to the spectrum of the ammoniated electron. (See, for example, KEENE,J. P., Rad. Res., 22,l (1964); G o ~ ~ s c h a lW. l , C., AND HART,E. J., J. Phys. Chem., 71, 2102 (1967); DOUTHIT,R. C., AND DYE,J. L., J. Am. Chem. Soc., 82,4472 (1960).) The complex rippling nature of the curves first published, moreover, has been shown to be due to a carbonate transient, nonuniform film response, or other experimental artifacts as suggested by Hart and Boag in their original papers. Smooth curves for solvated electrons have also been published for alcohols, amines, etc.
..
VIJAYMOHANBHATNAGAR To the Editor: Facult6 des Sciences de Taulouse I should like to thank Dr. Gottschall for drawing Toulouse, France attention to this aspect. My reference to the historically important curves of Hart and Boag tended to G.H., AND SALLEE, E. M., "Quantitative Chemistry," 'BROWN, imply that the structure they show is still regarded as W. J., AND MEPrentioe-Hell, Ind., 1964, p. 286. BLAEDEL, significant. LOCHE, V. W., "Elements of Quantitative Analysis-Theory and Practice," (8nd ed.), Harper and Row, 1963, p. 459.
EDITORS NOTE: Authors of the two textbooks referred to in Prof. Bhatnagar's letter agree on the following:
S. R. LOGAN UNIVERSITY OP STRATHCLYDE GLASGOW C. 1, SCOTLAND Volume 44, Number 12, December 1967
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