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N D E N G I N E E H I N G C I i E M 1 S T 1%1
a39
Corrosion of Metals by Milk
Editor of Induslrial and Engineering Clternislry: The arrangement with rotating specimens is, in general, nut h W l o ~of Induslriol a& Enginewing Chemistry: more satisfactory in the United States than in Germany. This .9paper on “Corrosion of Metals by Milk” [IYu. Euo. CKEM., is also pointed out in OUT paper in the second paragraph on page 341 where we say: “Because of the uncertainty in regard to ve24, 339 (1932)] deais with the effects of opernting conditions on the behavior of nickel, copper, and some alloys. The corrosion locity and agration in the above experiments, another experimental procedure was tried.” We then proofed t o describe our of milk a t different rates of sow was studied; for this purpose, tests were made with FL rotating spindle machine, the specimens continuous flow method which we belicve is much more satisbeing suspended in stirrups attached to the moving arm of the factory than the method describ-d by Goldbach. The rotating spindle experiments were included in our paper appar;utus. I n Germany, howevor, we consider an arrangement like this only because they represent a condition which may sometimes he riot quite reliable. For, if the specimens Bse moved, m is done found in a plant, and also hecause we m r e rather surprised t o in the above-mentioned investigation, a state may he reached find that reproducible results could be obtained by such a crude when the attacking agent is moving wit.11 nearly the same ve- and simple method of adjusting velocitieu, Goldbach’s note regarding weight loss determination us. visual locity as the specimens thernselvrs. In order to avoid this unu the change in weight does not certaintr. we keep the suecimens still. and :&ate the solution examination is correct in so far t
used. The specimens we fastened to a cage, the BOIUtion being moved by a stirrer. The daba derived f r o m such stirring tests give results in good ticcord with practical experience. F i g u r e 2 of the above paper, repres e n t i n g the effect of velocity on c o r m sion, shows 5 emvc which i n c r e a s e s slightly from 20 to 1 3 0 meters p e r m i n u t e , hut then drops. The use of the r o t a t i n g machine perhaps affords an explanat i o n f o r t h i s behavior. At a veSTIRRING APPARATUS locity of 20 to 130 meterj mer minute the specimens are rotating in a quiescent solution; with inereasing velocity, however, tbe agent itself hegins to move, thus lowering the velocity of the specimens. In evaluating the results, the authors of the paper tnok only the change of weight into consideration. According to our experiments, the judgment of the corrodibility based only on the change in weight does not always suffice. It may he sufficiont with even attack, hut in case of pitting8 and, above all, of intergranular deterioration the rate of corrosion cannot be calculated from these data. They should be supplemented by investigations of structure and physical properties of the specimens before and after the corrosion t&. Fm%herdetsils about corrosion tests in Germany may be found in the tentative standards elaborated by the German Reichsawschuss for Metallsohuta, translations of which hsve already been published in English and Ameriean journuh [ M e l d Progress, 20, No. 4,91 (1931); Ind. Chemisl, 7 (80), 379 (1931); Aireraif Eng. (Lrmdon),3, No. 30, 195 (1931)l. GEORGG o m m m Dsamcan VERSUCHBANBTLLT SOLI L o m r * s m n. Bmnux-Ao~snsnos,G S ~ M I N ~ .April 28. 1832
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would have complicated the paper tremendously without contributing anything to bring out, the point of the effects of operating conditions on corrosion in variaus parts of pasteurizing equipment. It would have shown numerous small pits with high currovion retos of nickel, no pitting a t loiv Corrosion rates of nickel, and no pitting with any of the other metals tested. Othor changes in structure and physical properties were nut investigated, &s they could hardly be expected in such short test8 as ours. In spite of the fact that the pitting wm of no particular importance, a note should possibly have been added to explain this, and we are grateful for this occasion to do so. E. A. TREBLEK N ~ ~ i o n rD f in r ~ rI’nonucia Conrona.rrov. isc.
B o m ~ o n Mo. ~.
Mar 14. 1832
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?‘lie Yellowing of Oils Owing to an unfortunste misunderstanding, Morrell and Marks, in condensing their original manuscript criticizing Elm’s puhlications on the above subject, changed the sense of their criticism materially by omitting a numher of essential points t o whioh reference iY made in Elm’s reply, printed a t the same time [INn. ENQ.CKEY.,24, 593 (1932)j. Elm’s reply, however, was printed in its original farm. This explains fully the apparent lack nf connection between these two notes. A. C. ELM Ter Nsw Jsnsrr Ziac C o . PA,,,,N, P*. May 25. 1932
Hydrolysis of Starch by Carbonic Acid In commenting OQ the article by M. A. Dewey nnd N.W. &me [Inn. ENQ.CKEY.,23, 1436 (l93l)l, it should be said that the saccharification of strtrcli by csrbonie acid under pmmue has some advantages over the usual hydrolysis by hydrochloric acid. A puretasting liquid is obtained; and the removal of the salts, obtained in the neutralization process, is avoided a t the plant. On the other hand, however, the equipment is larger and the reaction lasts longer. In both methods it seems that the deeoloratiun and subsequent filtration are not to be avoided. The method is, moreover, not entirely new, for in 1877 Bachet and Sitvalle, and in 1883Jacoh W. Decastro applied for patents. In the meantime, no practical application of these protected methods has been reported. A. P. 8CHULZ F o n s c m n o a n s s ~ ~riin ~ r Sria~m%aex~r&no.* S*awnmm= 13. B ~ n ~ rN65, w Qrrarmr April 13, 1832
