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1 . The simpler cases show the student that percentage as determined in a chemical analysis does not differ from the percentage he has been accustomed to work with since grammar-school days. 2. The use of chemical factors makes the computations for volumetric analysis directly analogous to those for gravimetric analysis. 3. They are not burdened with the necessity of learning the additional concept of equivalent weights and normality, for this has been shown to be totally unnecessary. W. P. CORTELYOU NEWYORKSTATE COLLEGE OF CERAMICS ALFREDU N I V B R S I ALFRED, ~. N. Y.
BALANCING CHEMICAL EQUATIONS DEARDR. KENDALL: * Protracted convalescence after a rather sharp attack of "flu" has given me the opportunity of reading more closely than might otherwise have EDUCATION. been possible the February issue of the JOURNAL OR CHEMICAL May I first of all take this opportunity of thanking you on behalf of myself and my colleagues of the chemistry department of Geo. Heriot's School for recommending the addition of the JOURNAL to school magazine lists. We adopted your suggestion and have had many pleasant and profitable hours in consequence. I had not noticed Mr. Endslow's letter to thereditor in the December issue, re "Balancing Chemical Equations," but reading the February number closely I came on the replies, including your own. It may be of interest to you to know that in Geo. Heriot's School-at least since the early days of the War-I have generally spent one lesson teaching to my Leaving Certificate Class this "Algebraical Method" of balancing. The objects in view have been mainly: 1 . To satisfy the more "mathematically minded" pupils that i t is generally possible to find the coefficients without resorting to what otherwise might seem to them a species of "juggling." 2. To point out that whereas the writing of a balanced equation may suggest a possible chemical reaction, this is a reversal of the proper order that a chemical equation should express quantitatively a change which has actually taken place. 3. To warn them that in many cases a textbook equation is only one of an infinite number which also seem possible. 'This letter was addressed to Dr. James Kendall. The University, Edinburgh, Scotland, and forwarded by him to the editorial office.
1300
JOURNAL OF CHEMICAL EDUCATION
JULY,1932
The topic generally arises during our study of the halogens where the textbook gives:
+
+
(a) 2KClOs = KC10, KC1 OX (b) 3KClOa 2HzSO4 = Kc101 2KHSOd H1O 2C101 (6) 4KC10~ 12HC1 = 4KCl 6H20 3CIOs 9Cl
+ +
+
+
+
+
+
+
From the point of view of "balancing" there is no possible substitute for (b), but instead of (a), since the method gives two independent equations for finding four unknowns 4KC10s = KClO,
+ 3KCI + 40a, (etc.)
seem equally possible, and similarly instead of (6) we may write
+ 2HCI = KC1 + HzO + CIOl + CI 2KC10a + 8HCL = 2KCI + 4Hz0 + CIOl + 7CI KCLO$
or
and so on. I don't know where I first came across the method-certainly not in "Walkerv-hut I have a clear recollection of reading-more than twenty years a g e a n application of the method to the practical problem of the complete combustion of gunpowder. Through the kindness of a friend I have the book in front of me now. It is entitled: "The Principles of Mathematical Chemistry," by Dr. Georg Helm, Prof. in the Royal Technical High School, Dresden, August, 1894, Translated by J. Livingston R. Morgan, Ph.D. (Leipzig), Instructor in the Brooklyn Polytechnic Institute (New York: John Wiley & Sons: Lopdon, Chapman & Hall, Ltd., 1st edition, 1897). It is a small book of about 200 pages. In the last chapter, "Chemical reactions that depend upon several parameters," I find this statement: " . . . It will be best illustrated by the example to which this method was first afified. Debus (Ann. Chem., 1882-91, Nos. 212-65) treated the reaction of gunpowder as a chemical reaction, which depends upon several variables, and Nickel (Z. phys. Chem., 1892ff.) treated other chemical technical processes from the same standpoint. " Potassium nitrate, charcoal, and sulfur form by explosion potassium carbonate and sulfate and persnlfide, carbonic acid gas, carbon monoxide, and nitrogen according to the reaction:
+
zKNOa+yC+sS = tKICO~+uKeSO~+wKSz+wCO~+aCO l / a x N ~
"We choose with Debus x = 16, and ask how the other substances are to be chosen so that the reaction may he complete. . . . . . " By making use of the principles of solid analytical geometry--"we can now give by aid of the figure the amounts of substances necessary for a complete reaction . . and Debus has proved that all the new powders belong to this plane, while the older mixtures are represented by points outside of it."
.
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I trust I have not bored you too much, but if you don't know the book and would care to look a t it I should he very pleased to send it on to you. I t is one of the "first thousand" c o p i e s 1 don't know whether there ever was a second thousand.
. . . . . .
DEARDR. GORDON: May I add that since writing Dr. Kendall I have found on my own book shelves a small hook on pages 8 and 9 of which may be found an example of the method, discussed above, fully worked out, with five problems included for practice. The book is "Physical Chemistry for Beginners," a translation into English (by the late Dr. R. A. Lehfeldt of the East London Technical School) of a German translation from the Dutch of Dr. Ch. M. Van Deventer, with preface by Van't Hoff-author's preface to the German edition dated from Amsterdam, 1897. The English publishers-Messrs. Edward Arnold & Co., 41 & 43 Maddox St., London, W1-tell me that they first published the book in November, 1898. Yours faithfully, JOHN H. MELVILLE GEO.HERIOT'SSCHOOL EorNauRcx, SCOTLAND
