COMMUNICATION TO THE EDITOR
715
ponent in the liquid, as abscissa, a straight-line relationship is obtained, the line making an angle of 45' with the z-axis. Grateful acknowledgment is made to Mr. Ralph Petri for his assistance in carrying out much of the laboratory work. REFERENCES (1) T E A Y ~ R J.:Phys. Chem. P, 382 (1898). (2) T Y ~ R J.:Chem. Soc. 101, 81, 1104 (1912).
COMMUNICATION TO THE EDITOR T H E REACTION BETWl3EN BASIC ALUMINUM SULFATE AND HIDE SUBSTANCE' The statement is made by E. 0. Wilson and S. C. Yu (J. Phys. Chem. 46,166 (1941))that the method employed by us in determining the composition of the chromium compound fixed by animal skin in making leather (J. Phys. Chem. 41,961 (1937))is of doubtful value. They give two reasons for their doubt: ( I ) Their enlarged log/log plot of the values for acid SO, fixed uersus acid SO1 free does not give a single straight line. (2) The equation b = RC, which they develop from the equation i = K Q m ,is not in the form of the Freundlich equation. Since the doubts of Wilson and Yu are based upon their errors of plotting and errors in calculation, we shall appreciate the opportunity of correcting them. ( I ) If one compares their plot of the acid SO, points (their figure 8) with our plot of the same points (J. Phys. Chem. 41, 961 (1937)),it is at once apparent that theirs is not an enlarged but a condensed plot. On their plot, all of the values for the 0.4per cent basic liquor have erroneously been shifted one cycle to the left. Taking the first point, for example,which is 5.03 g. fixed and 2.50 g. free,-their plot shows 5.03 g. fixed and 0.25 g. free. Shifting this set of values one cycle to the right, where it belongs, brings them into line with the values for other basicities. I n view of the complicated physical structure of animal skin, the closeness of the sixty-nine points (derived from chrome liquors varying from 0.4 to 46.0 per cent basic) to a common line is noteworthy. (9)The errorin thiscase is in assuming that their derived equation b = RC is 8 general equation for all values of b and c. They state in their derivation that for any single point, i, (not every point) on the line, i = R(j)":the equation for Cr2Os fixed uersu~CrsOa Received January 22, 1941.
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NEW BOOKS
free is b = RC. This limits the equation b = RC to points which a t the same time fix only one definite amount of acid SO4. This makes the amount of acid SOr fixed a constant value, and the equation b = RC is therefore not general, but specific. As a result of this, there will be a series of equations bl = RIC1,bt = R&, b, = RnC,, the plot of each equation passing only through its corresponding point illiz,or inand no other i point. These equations with the above limitations fit the data obtained by us. If the equation b = RC were general, 'it would have to hold for every value of i. Since i is governed by the equation i = K(j)m,then the two equations would have to be equal: b = RC = i = K ( j ) ,
then
i = b but
i = b(y -
2)
(by definition)
Therefore the assumption that b = RC is a general equation is false. The equation b = RC will therefore not be in conflict with the Freund~ the above-mentioned limitations are taken lich equation b = K ( C )when into consideration. Like the equation b = RC, the Freundlich equation, b = K(c)", which we employed is specific for a given basicity. DONALD H. CAMERON. GEORGE D. M C ~ U G H L I N . B. D. Eisendrath Memorial Laboratory Racine, Wisconsin
NEW BOOKS LYNN. Experiments in Colloid Chemistry. By ERNESTA. HAUSERAND J. EDWARD 178 pp.; 70 fig. 5 x 7 in. New York and London: McGraw-Hill Book vii Company, Inc., 1940. Price: $2.00. Whereas in radioactivity or in nuclear physics the essential facts are deduced in an abstract manner by long trains of thought from the readings of our instruments, i t is the privilege or, perhaps, the weakness of colloid science that, as in biology, there is not yet such a strong background of powerful theory and that, therefore, the observations as such still represent a large part 9f our knowledge. The colloidal chemist must, therefore, keep in mind many experiments, often of very different kinds, and he must always refer to them. He will thoroughly enjoy a book like that by E. A. Hauser and J. E. Lynn, which contains more than two hundred characteristic and often striking experiments in colloid and capillary chemistry. The experiments are well selected and well described, and many are new or not generally known. But he will find the book also very valuable in a deeper sense, whether he is a beginner or has been long familiar with this field of work. H. FREUNDLICH.
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