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error of attempting t o explain commercial observations by the results of laboratory experiments made under conditions not closely related t o those met in commercial practice. Strictly speaking, the corrosion of the iron in an iron-tin couple should be inappreciable as long as i t bears a cathodic relation to the tin. Except in electrolytes possessing a high conductivity, however, this condition is not attained unless all portions of the cathodic iron are in very close proximity t o the anodic tin. I n case parts or all of the iron element are located at appreciable distances from the anodic tin, the protective influence of the tin is lost and corrosion of the cathodic iron occurs as a result of “local action.” This is the situation encountered in the type of iron-tin couples which Kohman and Sanborn used in their experiments except in those cases where the area of the iron element was very small as compared with the area of the tin element. Kohman and Sanborn’s results show that where the ratio of the area of iron t o the area of tin was 0.0413 or less there was no corrosion of the iron. Had they altered their technic so that, regardless of the relative area of the iron element, all portions of it would be at no greater distance from the tin element than that existing in the couple of the above-mentioned ratio of iron t o tin, they would have found that variations in the relative areas of cathodic iron t o anodic tin have no i d u e n c e on the corrosion of the cathodic iron. In no case would there have been any appreciable corrosion of the iron. As stated above, Kohman and Sanborn found no corrosion of the iron where the ratio of area of iron t o area of tin was 0.0413 or less. I n a normal can this ratio is even very many times less than the smallest ratio employed by these authors. Consequently, any variation in the relative areas of iron base and tin coating exposed in a tin can t h a t would be met in commercial tin plate would not be expected t o influence the rate of corrosion of any microscopic areas of exposed iron. Obviously, the observed effect of increased weight of tin coating in delaying the perforation of the tin cannot be explained by a cathodic relation of iron base t o the tin coating. Experiments in the writers’ laboratory have indicated that, under conditions favoring the corrosion and perforation of tin plate, the iron base retains its normal anodic relation to the tin coating. On this basis there is no difficulty in explaining perforation of tin plate. It is a common observation in the canning industry that inside-enameled cans perforate more rapidly than plain cans. Kohman and Sanborn have attempted to explain this on the assumption t h a t in the enameled can the area of tin coating relative to that of the exposed iron base is reduced. This view is open t o the same objections as their attempt to explain the effect which increase in weight of tin coating has in delaying the perforation rate. There is a strong possibility that the enamel film itself may behave electrochemically towards areas of exposed iron base. Walkers pointed this out for the first time in 1909. He showed that in potassium chloride solutions can-enamel films are definitely cathodic t o adjacent areas of uncoated iron and consequently intensify the corrosion of exposed iron with which they are in contact. Walker’s work is being repeated in this laboratory in solutions of the fruit acids having approximately the same hydrogen-ion concentration as the fruit juices. Can i t be demonstrated that commercial enamel films behave cathodically t o adjacent areas of uncoated tin plate or black iron under the conditions existent in a can of fruit, it becomes a simple matter t o explain the fact that enameled cans perforate more rapidly than plain cans. ROGERH. LUECK HAROLD T. BLAIR AMERICAN CAN COMPANY SANFRANCISCO, CALIF.,AND MAYWOOD, ILL. January 17, 1928 6
Walker and Lewis, J. Ind. Eng. Chem., 1, 754 (1909).
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Editor of Industrial and Engineering Chemistry: Corrosion in canned foods is an exceedingly complex process, influenced by numerous factors. It is not likely that any one factor is dominating throughout the life of a can. In our paper, “Tin Plate and the Electrochemical Series,” t o which Messrs. Lueck and Blair refer, we had occasion t o discuss but one factor. Our data and our procedure in securing it are in sufficient detail‘ t o speak for themselves. We will await with interest the promised publication of t h e data sustaining the various points h e c k and Blair have made. E. F. KOHMAN NATIONAL CANNERSASSOCIATION N. H. SANBORN 1739 H ST., N . W. WASHINGTON, D. c. February 28, 1928
Definition of “Atomic Volume” Editor of Industrial and Engineering Chemistry: I read with great interest and appreciation the article entitled “Surface Tension of Metals with Reference t o Soldering Conditions,” by A. W. Coffman and s. W. Parr, which appeared i n the December issue [Ind. Eng. Chem., 19,1308 (1927)l. The authors quote Smith for the hypothetical statement t h a t “the larger the difference in atomic volumes and surface tensions between two metals, the more of a decrease will be obtained in surface tension upon alloying the two.” They also give a table of surface tensions and (supposedly) atomic volumes of some of the metals and from it deduce t h a t thallium should form better soldering alloys when alloyed with tin, bismuth, or antimony than our existing solders. I have added the word “supposedly” advisedly, as the term “atomic volume” which they employ is not the same as the one generally understood and which was used by Smith, being by definition “atomic weight divided by specXc gravity.” I feel that the authors should have given their reasons for this substitution of terms, as it is by no means sure t h a t Smith’s hypothesis holds good when atomic volume is considered as “the approximate volume of any atom, denoting that portion of space required for its existence, which is doubtless equal t o the space within the outermast shell of electrons.” [The words quoted are taken from a n exposition of Bragg’s theory b y Winchell, Science, 61, 553 (1925)l. The new term is usually called “atomic domain” and there are several objections to its use in connection with Smith‘s theory: 1-There are possible variations of 25 to 30 per cent between calculated and some of the observed volumes of the atom taken from the supposed diameters of the atoms, the diameters being the distance between the centers of the positive nuclei of adjacent atoms. 2-“It is shown that the relation is less accurate when applied to crystals of metals, which in Langmuir’s theory consist of a n assemblage of positive ions held together by electrons which have no fixed positions in the structure.” [Bragg, Phi!. Mag., 40, 169 (1920)l. The following table of calculated atomic volumes as employed by Smith in stating his hypothesis is given for several of the metallic elements. Upon this basis the variation of atomic volume between thallium and tin, bismuth, or antimony is slight, disproving the belief that binary alloys of thallium with the above metals will have greatly reduced surface tensions and consequent superior solder qualities. At the side are given the authors’ figures for atomic volume. METAL Lead Tin Antimony Bismuth Thallium
ATOMIC WEIGHT SPECIFIC GRAVITY 18.2
17 18 21-22 17.2
NATIONAL LSADCOMPANY 106 YORKSr., BROOKLYN, N. Y. December 29, 1927
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FRANK H. EDWARDS
April, 1928
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Editor of Industrial and Engineering Chemistry: I wish to note with appreciation the communication by Mr. Edwards relating to the paper on “Surface Tension of Metals with Reference t o Soldering Conditions.” In so far as his criticism relates t o the subject matter of the article, our only reply would be that we are equally aware of the meager information set forth in the paper. It is a new field of study and promises t o have many important technical applications in metallurgy, and any interest we may have started is in itself a source of satisfaction t o the authors, but still more so if Mr. Edwards or others who may be interested will carry the work further and expand the area of our information in that particular line. UNIVERSITY OF ILLINOIS
URBANA, ILL.
S.W. PARR
February 28, 1928
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Corrections In our paper entitled “Pigment Reenforcement of Reclaimed Rubber,” Iitd. Eng. Chem., 20,134 (1928), the sentence beginning in the last line of the first column on page 137 should read as follows: “The resistance t o tear (Figure 31) is slightly improved. Both accelerators give a higher stress-strain curve with 10 volumes of carbon black (Figure 28), but with 20 volumes Safex does not give any higher stress-strain curve than when no accelerator is used.” H. A. WINICELMANN E. G. CROAKMAN A slight addition should be made to Figure 3 of the article on “Measurements of Surface Temperature,’’ Ind. Eng. Chem., 20, 127 (1928). Owing to a n error in drafting, the line representing the copper return wire from the ice bath to the switchboard was omitted. This would be corrected by drawing a line from D to the selective switchboard. D. F. OTHMER
BOOK REVIEWS Colloid Symposium Monograph. Volume V. Papers presented at the Fifth National Symposium on Colloid Chemistry, University of Michigan, June, 1927. Edited by HARRY BOYER WEISER. 390 pages. The Chemical Catalog Company, Inc., New York, 1928. Price, $6.50. Under the title “Unity in the Theory of Colloids” Professor Kruyt, the guest of honor, develops the thesis that colloidal solutions, both lyophobic and lyophilic, may be treated from a common viewpoint. In both groups the particles are said to be polymolecular, and the electrical behavior is interpreted as electrokinetic or electrocapillary in character. On a thermodynamic basis no continuity is recognized between true solutions and colloidal solutions. When these views are compared with those presented by Professor McBain, guest of honor a t the 1926 symposium, the differences in opinions reveal a healthy state in this branch of science. I n a subsymposium on plasticity or consistency, methods are discussed by Giesey and Arzoomanian, Phipps, and Speicher and Pfeiffer. A descriptive treatment is given for casein-glue systems by Browne and Brouse, and for cellulose derivatives by Bingham and by Sheppard, Carver, and Houck. The theories of solute-solvent relationships are briefly reviewed, but no mechanistic interpretation of the phenomena is offered. Most of the important topics of colloid science find some mention in the remaining papers. Various aspects of sorption are discussed-on crystals by Saylor, on de-ashed charcoal by Miller, a t mobile interfaces by Harkins, in gelatin systems by Ferguson. and in color lakes by Weiser and Porter. Certain soap gels are described by Holmes and Maxson; the transport of materials through various kinds of membranes is discussed by Michaelis, Bancroft and Nugent, and Stamm; and emulsions receive brief attention from Harkins. The technical significance of colloids is revealed by Blum in connection with the electrodeposition of metals, and by White in the aging of Portland cement. Colloids and biology are brought together by Robinson in a discussion of winter hardiness of insects and by Bancroft in a consideration of kidney secretion. The constitution of the nitrated celluloses is analyzed by Craik. A controversial tone is evident in discussions of lyotropic series and combination of proteins with electrolytes (Ferguson and Gortner, Hoffman, and Sinclair), the constitution of the color lakes (Weiser and Porter), and the stability of colloidal suspensions (Kraemer). It is unfortunate that the division of forces in the adsorption us. chemical compound issue happens to be so lopsided. The chemical interpretation is certainly capable of a more adequate defense than it receives. Perhaps a t some future symposium opportunity may arise for a detailed interchange of views with provision for recording prepared questions and answers. The removal of unnecessary mutual misunderstanding would liberate much energy-now going into fireworks-to more productive activities in fields a t present neglected. Peptization is given specific attention by Craik, Gortner et al., and Sheppard et al. Previously unpublished work of technical interest is found in the plasticity papers and Weiser’s contribution. Of theoretical as well as technical importance is Bartell and Osterhof’s excellent paper on adhesion tension of solid-
liquid systems. The correlation of adsorption and energetics by these authors accomplishes for immobile interfaces what Harkins presents for mobile interfaces. Taken together, the papers demonstrate again the wide ramifications of colloidal science. These annual publications serve well to record the trend of thought and productivity of a considerable body of those engaged in cultivating this particular cross section of physics and chemistry. E. 0. KRAEMER Fundamentals of Dairy Science. By Associates of LORE A. ROGERSin the Research Laboratories of the Bureau of Dairy Industry, U. S. Department of Agriculture. A. C. S. Monograph No. 41. 15 X 23 cm. 528 pages, 31 figures. The Chemical Catalog Company, Inc., New York, 1928. Price, $5.50. This is a tremendously worth-while book. In view of the extent and importance of the dairy industry, it is surprising that we have had t o wait so long for a work of this type and scope. Perhaps no one person felt qualified to write a book which would be anlauthoritative presentation of the various phases of the dairy industry. The present volume is fittingly written by a group of research workers who have at some time been associated with L. A. Rogers in the Bureau of Dairy Industry. Space will not permit the listing of all those who have contributed, but such names as A. 0. Dahlberg, E. 0. Whittier, W. M. Clark, G. E. Holm, L. S. Palmer, J. M. Sherman, S. H. Ayers, Charles Thorn, and E. B. Meigs are alone sufficient to give the book the scientific standing which it deserves. The title is perhaps somewhat broader than the contents, for “dairy science” might well include the nutrition and management of the dairy herd as well as manufacturing methods and t h e economics of production, whereas the volume is corhned to milk and milk products. The book is divided into four sections: Part I, The Constituents of Milk: Part 11. The Phvsical Chemistrv of Milk and Milk Products; Part 111, The Microbiology of-Milk and Milk Products; Part IV, The Nutritional Value of Milk and Milk Products and the Physiology of Milk Secretion. No book is ever perfect, and every work by a score of collaborators will obviously possess some outstanding chapters with others that, perhaps because of their proximity, are not so satisfactory. The reviewer believes t h a t Part I11 and the first chapter of Part IV are more truly “monographic” than are the rest of the book. Indeed, Chapters I and I1 appear to have been so condensed that they have suffered both in presentation and usefulness. Thus, the enzymes of milk are discussed and dismissed in slightly more than three pages. The statement (page 28) that galactase has an “optimum temperature from 7’ t o 42 is loose terminology, for it is well known that the optimum temperature of an enzyme can only be defined when we hold constant all other variables, including time. In the chapter on milk f a t the condensation has even been carried to the point (page 78) of using incomplete sentences. In the discussion of the proteins of milk the alcohol-soluble protein, isolated by Osborne, is not mentioned. Less than five pages are devoted to the industrial O”
