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Volr 19, No. 9
tem and on the efficiency of regeneration of zeolites6 in waters-ftening plants. OTHER AppLIcmIoPu‘s-Hydrogen-ion controI has been applied with equally good results to sewage and industrial waste disposal; pulp and paper manufacture; sugar manufacture and refining; manufacture of dyes and their application to fabrics; manufacture of pigments; nickel and acid zinc plating; ceramics; canning of food products; gelatin
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Sweeney and Riley,
THISJOURNAL, 18, 1214 (1926).
and glue; flour, dough, and bread; crackers; tanning of leather; pharmaceuticals general chemicals such as lithopone, alum, etc.; candy; milk a n d milk products such as butter, cheese, acidophilus and buttermikk; fermentation, bacteriological and pathological work, etc.; but space will not permit their discussion. It will be seen that the application of this control method is practically universal, as it must be, since acidity and alkalinity are important to almost every chemist and manufacturer.
Copper as an Industrial Contaminant in Foodstuffs’ By C. G . King and G. Etzel DEPARTMENT OF CHEMISTRY, U P I V E R S I T Y OR PITTSBURGH, PITTSBURGH, P A .
MPORTANT objections to an appreciable increase in the copper content of foodstuffs may be considered under the following headings: (1) the direct poisoning effect upon the body,2 (2) a tendency to cause or accelerate the development of disagreeable flavors, ( 3 ) an acceleration of the destruction of vitamin C,4 and (4) the production of “off” color.5 Factors connected with (2) and (4) are generally recognized in plant practice, because their relationship to the market value of products is fairly obvious. However, (1) and (3) are not so obvious and are liable to be given less consideration than they deserve. F. B. Mallory, who has furnished the most careful evidence relative to cumulative copper poisoning, estimates that more than 5 to 10 mg. per day may produce toxic results. This is a much lower limit than that previously estimated by other investigators whose observations were not so complete.6 Hess4 has shown that small amounts of copper (2.5 p. p. m.) may accelerate the destruction of vitamin C in milk. If the same phenomenon occurs in fruits and vegetables it would be an important factor to consider in their preparation, since it is difficult to conserve their vitamin C content.
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Experimental The present investigation deals with the copper content of three types of foods commonly prepared in copper or brass equipment: (1)four groups of acid fruit products representing different trade practices, (2) milk from nine different plants, and (3) carbonated beverages from two plants. The xanthate method of determining copper’ was used, chiefly because of its sensitivity, and experience showed it to be suitable for this purpose. It is sensitive to 0.005 mg. in 50 cc. and gives accurate results when adequate precautions are observed. PRECAUTIONS-( 1) Contrary to statements in the literature,‘ nickel gives a color intensity and shade very similar to copper. Where nickel is present in significant amounts, another method must be used or the nickel must be removed before determining copper. 1 2
Received April 27. 1927. Mallory, Mellon Lecture, School of Medicine, University of Pitts-
burgh, 1925; A m . J . Path., 1, 117 (1925); Arch. Jnlernal Mcd.. 37, 336 (1926); J . A m . Med. Assocn., 86, 1552 (1926). 8 Emery, U. S . Dept. Agr., Bur. Animal I n d . , Ann. Report, 1909, p. 265; Emery and Henley. THISJOURNAL, 14,937 (1922); Supplee and Bellis, J. Dairy Sci., 6 , 455 (1922); Rice, Ibid., 6,262 (1923); 9,459 (1926). 4 Hess, THISJOURNAL, 13, 1115 (1921); J . A m . Med. Assocn., 82,
952 (1924). Null. Canners’ Assocn., Bull. 6 (1915). Drummond, J. State Med., 32, 382 (1924); Rost and Weitzel, Arb. Reichsgesundh., 61,494 (1919);Panton, Phorm. J., 110,393 (1923);Lehman, J . Chem. SOC.(London), 70, 486 (1896). 7 Supplee and Bellis, J. Dairy Sci., 6 , 455 (1922); Scott, “Standard 6
8
Methods of Chemical Analysis,” 4th ed., p. 197.
(2) The use of brass burners for ignition may introduce appreciable quantities of copper; hence it is recommended that all drying and ignitions be carried out in electric ovens or muffles. (3) High concentrations of other salts may affect the color intensity and produce turbidity. (4) Fresh xanthate solution should be made up every few days and the dry salt (KOEtCSz) should be prepared or recrystallized every few weeks. Otherwise a faint cloudiness interferes. ( 5 ) All water used, even for rinsing apparatus, should be especially distilled. That from the usual copper still with blocked tin condenser and piping gives a distinct color with the reagent.
PROCEDURE-Auniform sample was removed from the glass container, weighed, evaporated to dryness in silica or porcelain dishes in an electric drying oven, and then carefully ashed in an electric muffle furnace. The ash was dissolved in hydrochloric acid, diluted, filtered, and any residue reashed and complete oxidation secured when necessary by the addition of one or more drops of nitric acid. The filtrate was evaporated nearly to dryness, redissolved in water, made alkaline by addition of an excess of concentrated ammonium hydroxide, and filtered. For products with comparatively large amounts of copper, the residue was redissolved in hydrochloric acid and again precipitated and the filtrate combined with the first. The excess ammonia was evaporated over an iron hot-plate, the solution made neutral or very faintly acid with dilute acetic acid, and either used directly for developing the color (for milk and beverages) or made up to volume and an aliquot taken (for fruit products). Color comparisons were made in 50-cc. Nessler tubes after the addition of 10 cc. of 0.1 per cent xanthate solution. Standards were prepared at the same time having 0.5, 1.0, 1.5 to 12.0 cc. of fresh copper sulfate solution, 1 cc. of which contained 0.01 mg. of copper. Results Each value given in the tables represents at least two determinations on each of two samples taken. Only one significant figure is given in most cases because of the variations found in different samples from the same source. FRUITPRODUCTS-The differences shown in Table I are due mainly to variations in care and type of equipment, rather than to such factors as time and temperature of heating or composition of the raw materials. Contrasts in sanitary practice were as striking as contrasts in copper content. The chief factors involved seemed to be (1) protection of copper equipment by tin or other metal, (2) thoroughly cleaning all copper surfaces between batches, (3) keeping exposure to the air a t a minimum, and (4)allowing only the minimum of time of contact with copper beyond that actually needed for cooking. A separate study of each factor was not made, but it appeared that (1) and (2) were
INDUSTRIAL A N D ENGINEERING CHEMISTRY
September, 1927
1005
Pasteurized M i l k PROCESS4 Max. Av.
USUAL
Min. T a b l e I-Copper PLANT 1
Found in Fruit Products P. p . m.
Strawberry preserves Blackberry preserves Cherry preserves Apple butter Chile sauce Ketchup
PLANT 2
C u r r a n t jelly Raspberry jelly Kaspberry preserves Peach preserves Strawberry preserves Blackberry preserves Apple butter Grape j a m Chile sauce Ketchup
4 4 3 3 7 8
PLANT 3
P. P . m.
Plum jelly Strawberry jelly Raspberry jelly Raspberry preserves Apple b u t t e r Chile sauce
-A
45 110 18
PLANT 4
2 7
Raspberry jelly Raspberry preserves Blackberry preserves Cherry preserves Strawberry preserves Apricot preserves Plum preserves Peach preserves Pineapple preserves
6 10 3 24 4 8 12
4
4 9 11 6 4
Apple cider concentrate ( a ) Apple pulp ( b ) Finished apple butter (1a:lOb) Tomato pulp Same a f t e r cooking approx. 1 . 5 hours
Raw T o p of cooler Bottled
P.9.m. 0.40 0.45 0.48
P.0.m. 0.60 0.70 0.72 Raw M i l k
P.p.m. 0.47 0.60 0.62
ELBCTROPURE PROCESSb
P.9.m. 0.45 0.60
0.52
Average of five samples delivered b y farmers t o receiving station: Kaw , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . O . 43 p. p. m. Same after screening., , . . , . ,. , . . . . , , , . , , , , , . , . . , . . O . 45 p. p. m. Average of three small batches screened a f t e r copper screens had stood e r posed t o air for about 5 minutes between loads. . . . . . . . , . O . 97 p. p. m.
Condensed M i l k Average of three samples of skimmed milk, condensed t o 36 per cent total solids in copper vacuum p a n s . , . . . , , , , , . . . . , , . , , , . . 3 . 7 p. p. m. 0 -4verage of duplicate tests a t five plants, pasteurizing 30 minutes at 1 4 2 O F. in tin-lined vats and using tin-lined copper piping. b Average of two plants, heating t o 162’ F. between carbon electrodes.
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3
TESTS D C R I N G P R E P A R A T I O I7 I N COPPER EQUIPMENT
Plant A P. b . m.
C o n t e n t of Milk
T a b l e 11-Copper
the most important. Differences in acidity may also have had a minor influence.
Plant B I’. b. m.
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Eating a hundred grams per day of such products as those from Plant 3 would alone cause one to exceed the limit of copper previously suggested, without considering 1 hat which n-ould normally be supplied in natural foods.* Incidentally, this brand was the cheapest of the group and that of Plant 1 the most expensive. hIIm-The results of the tests on milk (Table 11)correspond closely with those obtained by Supplee and Bellis. The smaller amount of copper getting into the milk during Electropure pasteurization is probably due to the shorter exposure to metallic equipment while hot, as the extent and condition of the piping was similar. The copper content of milk is especially important in its effect upon flavor. McHargue, J . Agr. Research, 30, 193 (1925); Guermont, Compt rend, 111, 196 (1920); Maquenne and Demoussy. I b z d , 170, 87 (1920). 8
C A R B ~ S A T E D BEVERAGES-T~~ tests on carbonated beverages (Table 111) show that normally very lit’tle copper is dissolved. I n general practice the first few bottles of each run are discarded to avoid mixing of sirups, so that those which contain appreciable amounts of dissolved metal are automatically discarded. Since such beverages are always prepared cold, with little access of air, and are exposed t’o the metal for only a short time, little contamination wibh copper would be expected in normal plant practice. T a b l e 111-Copper
Lemon s o l a Cream soda Cherry soda Oranze soda Grape soda Coca Cola Root beer
F o u n d in C a r b o n a t e d Beverages P r o d u c e d i n Brass E q u i p m e n t Plant I Plant I1
P . p . m. P. p . m. 0.5 First bottle of lemon soda a t be0.3 ginning of run 0.8 0.5 0.4 F i f t h bottle 0.6 0.5 0.6 After 20 minutes’ continuous run 0.5 0.5
P. p . m. 0.9 0.7 0.6
Acknowledgment
The authors wish to acknowledge the assistance given by
P. A. Zook and TV. H. Busch in supplying some of the materials for analysis.
Adhesives and Adhesion‘ Mechanical Properties of Films of Adhesives By J. W. McBain and W. B. Lee UNIVERSITY OF BRISTOL,ENGLAND, A N D STANFORD UNIVERSITY, CALIF.
REVIOUS papers have
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demonstrated the significance of the determination of tensile strength of adhesives and have provided a ready routine method for The presthis purpose.’ t o ent paper indicates the importance of the study of other mechanical properties of films of adhesives, such as elasticity, brittleness, flexibility, ductility (in general “deforma b i l i t y ” ) , relaxation, and
Typical and significant data are presented for the mechanical properties of a number of adhesives and adhesives with added substances. The observations emphasize the essential importance of ”deformability” of an adhesive. Both this and tensile strength depend upon such factors as degree of humidity. The brittleness of an adhesive film may be greatly increased or entirely eliminated by appropriate additions. The strongest adhesive film here measured is isinglass with a tensile strength of 8 tons to the square inch in an atmosphere of 0 per cent humidity; the weakest are the gums and sodium silicates with a tensile strength of only a few hundred pounds per square inch.
Received M a y 9 , 1927. Investigation undertaken for t h e A4dhesives Research Committee of t h e Department of Scientific a n d Industrial Research, Great Britain, and published b y permission of this Department.
*
McBain and Hopkins, J . Phys. Chem., 29, 197 (1925).
6
Second Report of Adhesives Research Committee, 1926, p. 34. McBain and Lee, J . so
