Commercial Casein Relationship between Laboratory Tests and Coating Quality E. 0. WHITTIER,S. P. GOULD,AXD R. W. BELL,Bureau of Dairy Industry, 31. B. SHAWAKD G. W. BICKIKG,Bureau of Standards, Washington, D. C.
T
HERE are a t present no
western; some were produced by The coating quality of commercial caseins generally r e c o g n i z e d manufacturers with reputations differs considerably but the major differences standards for g r a d i n g for producing high-grade casein cannot be related to the chemical composition or to casein intended for use in coatand some, l o w - g r a d e casein; fhe customarily determined physical properties ing paper. Several of the paper they were of t h e t h r e e m o s t of the caseins. Hydrochloric acid caseins and companies have somewhat tentacommon types-grain-curd hytive specifications which they drochloric, self-sour, and sulfuric. self-sour caseins yield coatings differing in use to guide them in purchasing A comparatively small number smoothness and surface sizing. Both poor and casein; others rely on the ability of samples of sulfuric casein was good caseins were found among samples made of one producer to maintain included on account of the relaby each of the commonly used methods. Laborauniformity in his product. Such tively small quantity of casein of tory determinations and results of coating tests reliance is usually justified, althis type used in coating work. though occasionally the m o s t On the basis of laboratory deterare gicen in detail on thirteen commercial caseins careful manufacturer has a n inminations, samples which dupliand on fiee caseins made by different methods ferior batch of c a s e i n . T h e cated others were discarded and f r o m the same lot of milk. The significance and favor in which Argentine casein thirteen samples retained from limitations of tests on casein are discussed. has been held b y some of the the investigation. To them were coated-paper manufacturers is added one prepared especially b v probabfy &e to the uniformity obtained by blending of many S. A. Hall and one used in previous work-by t h e B u r e a u i f small lots. Standards (J), which was therefore of known paper-coating The fundamental purpose of the Research Laboratories of quality. Later, samples 18t o 22, inclusive, were prepared b y the Bureau of Dairy Industry in undertaking work on casein C. S. Trimble from one lot of milk b y different methods. I n has been t o increase the volume and the value of domestic this way the possibility of influences of differing milk source casein and thereby improve the financial condition of the was eliminated, and i t became possible to evaluate differences dairy industry in this country. This article is a n attempt t o in methods of manufacture. The histories of the samples are correlate characteristics of finished coatings, properties of omitted from this article, since they are practically of no aid coating slips, tests and analyses of caseins, and processes of in explaining the coating differences obtained. casein manufacture. It was felt that there was a definite advantage in carrying out this work in so far as possible LABORATORY EXAMINATIOPI’ OF CASEINS b y governmental agencies, in t h a t prejudices in favor of ~~PPESRASCE. -411 samples were free from vermin, other particular materials and methods would be avoided. foreign matter, and burned particles, except casein 5 which was Discussion of this paper is confined to casein of the type dirty and contained vermin, and 14 which contained burned particles. The color showed considerable variation, casein 14 precipitated b y acid. Casein precipitated from skim milk b y being especially highly colored. The dry samples had the the action of rennet is not included because i t is not used in characteristic, faint, not un leasant odor of properly handled paper-coating. “Acid” casein is precipitated by addition of any casein, except sample 9, whici had a definite sulfur dioxide odor. All samples were ground to pass a No. 20 screen. FINENESS. commercially available acid, usually hydrochloric or sulfuric MOISTURE. The moisture varied between 5.0 and 10.0 per or by development of lactic acid in the milk by bacterial accent. tion. Casein precipitated by souring of the milk by bacteria PH VALUE. The reaction of each casein was determined by is known as self-sour or lactic casein. The final reaction of the method of Watson ( 7 ) , on a small sample intimately mixed with quinhydrone and a few drops of water. The values found whey from self-sour casein is usually in the range p H 4.6 to this and by the following determinations and tests are given in 5.0, and i t is necessary to heat or to stir the soft curdled mass by Table I. in order to separate the curd from the whey. If acid is added FREEACID. This determination was made as described by to skim milk until the reaction of the whey is approximately Bell and Gould (1). The results are reported as milliliters of p H 4.1, a granular curd, particularly easy to drain and wash, 0.1 N alkali required per gram of casein. ASH,CALCIUM OXIDE,PHOSPHORUS PENTOXIDE. The methods is formed. Casein made b y this method of precipitation is used for the determination of ash and of these ash constituents known as grain-curd casein. Hydrochloric acid is usually have been described by Gould and Whittier ( 3 ) . A column in used in making grain-curd casein, though any other acid may Table I is given to other ash constituents, determined by difbe employed. The curd, b y whatever process precipitated, ference. FAT. The modified Babcock method described by Suteris drained until free from the bulk of the whey, washed several meister was used (6). times with water, and pressed, usually overnight, to remove as SOLUBILITY. Solutions were prepared containing 24, 30, and much of the water as possible. The curd is then shredded, 40 grams of borax (Ka2B407.10HnO) per liter and were labeled dried at 130” F. (54” C.) on screen trays in a tunnel drier, “12,” “15,” and “20,” respectively. To 10 grams of a sample ground to pass a No. 20 screen were added 50 ml. of solution and finally ground to pass a No. 20 screen. 12; the mixture was stirred and placed in a water bath at 65” c . It was stirred continuously for the first 5 minutes and then every C.4SEIN SAMPLES 5 minutes for 15 minutes more. If the casein was then comTwenty samples of casein were purchased from casein pletely dissolved, i t was reported as soluble in 12 per cent borax, since 10 grams had been dissolved by a solution containing 1.2 manufacturers and available details on making were obtained grams of borax. If the casein did not completely dissolve, the at the same time. The samples came from the three principal test was repeated with the solution of the next higher concentraproducing sections of the country-eastern, central, and tion, and finally, if necessary, with solution 20. 904
August, 1933
INDUSTRIAL AXD ENGINEERIXG CHEAIISTRY
ADHESIVE STRENGTH.This determination v a s carried out substantially as directed by Sutermeister (b). ALKALI REQUIREMENT. This is the number of milliliters of 0.1 1V sodium hydroxide required to bring 100 ml. of a 9 per cent casein solution to a pH value of approximately 9.1. The solution prepared in this v a y was used for the viscosity determination. VISCOSITY. This determination was made by 1 he method described by Bell and Gould ( 1 ) .
TESTSAND C O A T I X G PROCEDURE PAPER.The base paper, or body stock, used for all the coatings was a representative commercial product bought from the stock of a, coated-paper manufacturer. Two determinations of its sizing value b y the curl method ( 2 ) gave 16.5 and 12.4 seconds; by the dry indicator method ( 2 ) , 10.4 and 10.3 seconds. Two determinations of the w i g h t of five hundred sheets, 25 X 40 inches, gave 53.1 and 49.7 pounds. MINERAL. A commercial coating clay t,hat had been found satisfactory in a previous investigation ( 4 ) was used. EQUIPMENT. The coatings were made on 21 semicommercia1 scale and under practical mill conditions. The equipment consisted of a 14-inch Waldron flat-bed brush coated with festoon drier and rewinder, mixing tanks, and a five-roll supercalender. Detailed description and photographs of the equipment have been published previously ( 4 ) . COATING PROCEDURE. The coating procedure was similar to the commercial pract'ice used in applying a single coating to paper ( 4 ) . I n order to determine the relative paper-cclating value of the caseins, all were submitted to the same procedure. The main purpose of these mill tests was the relative valuation of the caseins. Therefore, rigid uniformity in all details of technic was essential in order t h a t variations in results might be attributable only t o differences in the caseins.
903
meanir-hile. I t was brought into solution by the addition of the three solvents in the order-borax, soda-ash, ammonia, each dissolved in the stated amount of water. After the solvents had been added, the solution was stirred for 1.5 to 2 hours, warmed to 57" C. (135' F.), and screened through a No. 200 sieve. The screened solution after being cooled to room temperature was mixed with the clay slip. The mixture was agitated for 1.5 to 2 hours, screened, and applied to the base paper in the coating machine.
P a P E R bIIL1,
TABLEI.
L.4BOR.4ToRY
d combination of alternate steel and cotton rolls, 3 and 2, respectively, was used in calendering the coated paper, which 1%-aspassed through in the web. S o attempt was made to obtain a high glossy finish, since the smoothness imparted by light calendering is sufficient for general high-grade printing. TESTMETHODSAND RESULTS.Results of tests on the casein solutions, on the clay-casein slips and on the coated papers are recorded in Table 11. These tests were made a t the Bureau of Standards. The apparent relative viscosities of the casein solutions are recorded as the time required for 50 ml. of each of the solutions a t 26.5" C. (80" F.) t o flow through t h e 0.125-inch (0.32-cm.) bore of a tube 1.25 inches (3.18 cm.) long. The apparatus used consisted of a glass tube 0.5 inch (1.27 cm.) inside diameter and 23 inches (58.4 cm.) long, enclosed in a vertical glass water jacket and fitted a t the lower end with a rubber stopper containing a brass rod, 1.25 inches long, through which had been drilled a 0.125-inch hole. I n making the test, the tube was filled with the casein solution-approximately 90 m1.-and the time required for 50 ml. to run, with decreasing head, from the brass tube was determined. The container used for the clay-casein slip was of brass, 14.5 inches (36.8 cm.) long and 2.375 inches (6.03 em.) inside
DETERMISATIONS ON CASEISs
0.1 N FREEACID ASH
PER
SAMPLE
METHOD OF hfAXI-F.4CTEP.E
PH
GR~M
CASEIN M1.
ASH
CaO
%
%
1.20 0.60 0.44 0.40 1.98 1.06 2.00 0.44 1.66 1.28 2.06 2.68 2.40 3.56 2.34 0.62 0.60 0.86 0.20 0.78
2.17 2.12 2.32 2.03 3.37 2.83 4.58 1.86 2.36 3.97 2.66 2.92 2.97 2.88 3.92 2.33 2.08 2.61 2.06 2.44
0.28 0.20 0.34 0.03 0.65 0.49 1.53 0.03 0.16 1.09 0.38 0.48 0.53 0.41 0.98 0.29 0.06 0.49 0.20 0.37
Pi05 %
-
'C%~f
FAT
%
%
0.04 0.06 0.10 0.17 0.66 0.09 0.42 0.10 0.18 0.78 0.33 0.43 0.23 0.30 0.67 0.20 0.47 0.17 0.13 0.13
1.80 0.50 1.44 0.72 0.00 0.27 1.35 1.62 0.90 0.81 1.35 0.90 0.90 0.63 2.25
-VISCOSITYDETERYIYATIOSO l N a1 kali required per 9 ReitcVisgrams tion of cosity BORAX SOLY. STRENQTH casein Soh. (abs.) % boraz pH Centipotses
M1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 18 19 20 21 22
Unknown HC1 grain-(.urd HCl grain-curd HC1 grain-curd HC1 grain-curd HCI grain-curd HCI grain-(:urd HC1 grain-curd Sulfuric Sulfuric Self-sour Self-sour Self-sour Self-sour Self-sour Self-sour Self-sour grain-curd Lactic grain-curd HCI grain-curd HCI grain-curd
4.76 4.36 4.71 4.35 3.99 4.42 4.55 4.39 3.37 4.74 4.03 3.96 4.16 3.81 4.58 4.52 4.37 4.73 4.73 4.42
The relative amounts of clay, casein, and water in the coating slips were 100, 17.5, and 250 parts, respectively. The casein solution contained 100 parts of casein, 10 of borax, 5 of soda ash, and 2 of ammonia. The formula and method of preparation of the clay-casein mixture were as follows: Clay slip: 3000 grams clay, 3825 ml. water, and 10 ml. concentrated ammonia. The clay was soaked overnight in 3000 ml. of water. The additional 825 ml. of water were used the next morning to lqash the mixture into the agitator. The ammonia was then added, and the mixture agitated about 1.5 hours before the casein solution was added. Casein solution: 525 grams casein in 2000 ml. of water; 52.5 grams borax In 750 ml. water; 26.25 grams soda ash (58 per cent sodium oxide) in 750 ml. water; 11 ml. concentrated ammonia in 164 ml. water. The casein was soaked in the 2000 ml. of water for one hour at room temperature and was stirred
1.85 1.98 1.88 1.83 2.06 2.25 2.63 1.73 2.02 2.10 1.95 2.01 2.21 2.11 2.27 .84 .55 .95 .73 .94
20 15 15 20 15 15 15 15 20 15 12 15 15 15 15 12 15 12 12 15
9 9 9 9 10 10 11 9 10 11 9 9 10 11 11 9 9 10 8 9
8.0 8.2 7.5 8.7 10.4 8.7 9.1 8.1 12.0 7.3 10.3 11.9 10.9 11.8 8.6
9.25 9.06 9.10 9.18 9.10 9.30 9.09 9.16 9.10 9.28 9.16 9.32 9.49 9.02 9.06 9.21 9.09 9.21 9.12 9.17
19.1 18.9 13.3 20.1 9.2 10.0 Lumpy 21.9 14.5 14.1 12.5 8.2 11.5 10.7 7.1 10.8 9.7 7.8 22.4 8.0
diameter, and was not incased in a water jacket. Into this container was poured 1000 ml. of the slip at 80" F. (26.7' C.) and the time required for i t to flow through a 0.125-inch opening 1.25 inches long was determined. Here again the results are only comparative. Measurements of p H value were made b y the potentiometric method with a n antimony electrode. Densities were determined with a hydrometer. The measurements on the papers were made by standard paper-testing methods. The gradings of the coatings recorded in Table I1 were made by members of the Bureau of Standards staff. These ratings agreed closely with those made by several members of the Technical Association of t h e Pulp and Paper Industry. Other characteristics of the caseins apparent by observation during the preparation and application of the coating mix-
IN DUSTR IAL AND E NGI N EER I N G CH EM I S TR Y
906
Vol. 25, No. 8
TABLE11. COATING TESTSON CASEINS --DETERMINATIONS C A S E I N SOLCTION
COATING CASEIN RON pH
1 2 3 4 4 5 5 6 7 8 16 9 10 11 12 13 14 15 18 19 20 21 22 25 X
203 204 205 206 220
211 212 213 214 215 2 16 217 236 237 238 240 249 40 inches
9.15 9.10 9.14 8.86 8.86 8.28 8.32 8.88 8.50 8.68 8.86 7.76 9.10 8.50 8.25 8.32 7.98 8.70 8.80 8.68 8.93 8.76 8.57
Viscosity (relative) See. 33.6 20.1 37.8 64.4 62.0 15.8 Thick 25.4 53.6 48.6 27.3 23.0 49.8 16.7 19.6 31.3 16.4 26.2 47.8 59.4 38.4 49.7 53.4
ON
COATING MIXTURES-
-CLAY-CASEIN
pH
9.00 8.80 8.22 8.12 8.60 8.30 8.32 8.57 8.65 8.66 8.65 7.98 8.76 8.50 8.30 8.32 8.08 8.55 8.76 8.74 8.86 8.95 8.78
SLIP-
Viacosity (relative) See. Paper stock:
TENSILE BREAKING STRENGTH
WEIGHT
?%%.
120.0 116.0 124.0 124.8 122.8 111.8 132.0 118.0 116.0 125.2 115.4
600 BURSTING S H E E T S ~ STRENGTH
1.236 1,230 1.238 1.234 1.234 1,232 1.262 1,232 1.234 1.236 1.232
ture, but not measured numerically, were recorded in detail. (The authors will furnish copies of these records to anyone interested.) Slips from samples 4 , 8 , 9 , 14, 18, and 19 foamed badly during application to the paper.
EFFECTO F
DETERMINATIONS ON COATED PAPER
7
SOLVEXTS O N F O A h l I N G
Because foaming seems t o be the outstanding undesirable characteristic met in the use of casein for paper coating, and because there had been received suggestions as t o variations in recipe whereby it was believed foaming tendencies could be decreased, additional coating runs were made to determine the effects of such differences. These runs are described separately from those made for t h e purpose of comparing the caseins themselves, in order t h a t the reader may not confuse the two distinct purposes involved. A brief account of methods and results is as follows (more detailed data may be had from the authors): Slip 251 was made with casein 4 and with amounts of borax’ soda ash, and ammonia less than those in the regular runs. The pH of the slip was 7.68. Slip 253 was made with casein 4 and with amounts of borax, soda ash, and ammonia greater than those in the regular runs. The pH was 8.88. Slip 260 was made with casein 4 and with 5 parts caustic soda to 100 parts casein as the only alkali. The pH was 10.00. Slip 261 was made with casein 4 and with ammonia as the only alkali. The pH was 8.54. Slip 252 was made with casein 4 by a highly recommended commercial formula. For each 100 parts clay, 17.5 parts casein and 205 parts water were used. To dissolve the casein, 5 per cent of its weight of borax and 3.5 per cent of its weight of concentrated ammonia were used. The final pH was 6.65. Slip 262 was made with casein 4 by another recommended commercial formula. For each 100 parts clay, 17.5 parts casein and 250 parts water were used. The alkalies used were, based on weight of casein, 8 per cent borax, 2.5 per cent soda ash, 2.5 per cent trisodium phosphate, and 2.0 per cent caustic soda. The pH of the slip was 8.76. Its adhesiveness appeared not to be as good as that of slip 206 prepared by the regular method. All six of these slips foamed and gave unsatisfactory coatings. These formulas offer no advantages over the one used for t h e main part of this investigation. T h e results substantiate the belief that foaming of slips is caused b y some undetermined property of the casein, and t h a t i t is not attributable t o t h e reaction of the slip or to any specific alkali used in preparation of the slip.
DISTRIBUTIOX O F CASEINS O N PAPER While this work was in progress, the need was felt for a method t o show visually the distribution of casein in the
Pounds 53.1 49.7 66.3 65.8 68.9 64.6 69.7 66.7 70.0 69.8 70.2 71.4 67.2 68.0 68.2 62.4 64.4 65.0 67.1 64.9 67.4 71.0 65.9 68.7 67.1
Points 14.6 14.8 15.7 17.5 18.9 18.9 17.9 19.0 18.1 19.0 19.2 19.5 17.5 18.9 18.5 17.2 16.7 16.9 16.7 17.0 17.0 16.0 16.0 18.0 19.0
Machine direction Kg. 5.0 4.9 5.4 5.5 5.2 5.2 5.3 5.2 5.4 5.4 5.2 5.6 5.1 5.5 5.6 5.1 4.9 5.0 5.0 5.0 5.1 5.1 4.9 5.4 5.5
Cross direction
ASH
GLOSS
Kg.
70
%
1.8 1.9 2.1 2.1 2.1 2.0 2.0 2.0 2.1 2.1 2.1 2.1 2.0 2.0 2.1 2.0 2.1 2.0 2.1 2.1 2.0 2.0 2.0 2.1 2.0
9.76 9.60 26.0 24.2 28.2 24.1 26.9 25.5 27.2 26.3 26.3 28.0 25.1 23.9 23.7 22.1 24.4 24.5 26.8 24.3 26.0 29.4 23.6 27.7 26.1
72.2 70.0 73.0 68.8 72.4 73.4 75.7 72.7 72.3 72.3 75.0 72.3 75.5 73.8 79.2 77.0 75.7 76.6 79.0 78.0 76.0 80.0 75.0
QU.&LITY O f COATING
Go9d Fair Good Poor Poor Very good Very good Oopd Fair Poor Good Poor Good Good Good Good Poor Fair Poor Poor Fair Fair Fair
finished coating. Although the character of a coating can be judged fairly well b y looking a t and through the paper toward the light, this method does not distinguish sharply among unevennesses in distribution of casein, of clay, and of paper fiber. lLlagnification of the surface is not necessary, since the differences are macroscopic. Staining of the casein was advocated as a method of making evident the distribution of the casein exclusively. B. J. Howard of the Food and Drug Administration suggested Millon’s reagent for the purpose and i t was found to be satisfactory. Further technic of t h e test was worked out by the senior author of this paper. Millon’s reagent is prepared by dissolving 10 ml. of mercury 1x1 190 ml. of concentrated nitric acid. To this solution is added 380 ml. of distilled water and the whole thoroughly mixed. Samples of coated paper are immersed in this solution for 5
minutes, rinsed several times in water, and dried on a towel or on a window pane. The coatings are colored by the reagent a pinkish orange. The intensity of color of any area depends on the amount of casein on that area. These test papers disintegrate after a short time and, so cannot be used as permanent records. Since their color is uneven and resists the passage of the actinic or chemically active light rays, prints may be made on photographic paper, the test papers being used as negatives. Prints made in this way are shown in Figure 1. White indicates a comparatively large concentration of casein; black, absence of casein. A black spot surrounded by a white ring results from a broken airbubble in the coating. Calendering of a coating makes t h e casein distribution more even; consequently, the illustrations, prepared as they are from calendered samples, are much more favorable t o all the samples than prints from uncalendered samples would be. DrscussroN
OF RESULTS
Extensive and detailed data have been given in order that persons interested may analyze them with thoroughness and draw conclusions independently. It is believed that the results of this paper may be used b y paper-coaters to substantiate or t o controvert a number of their own beliefs as to the influence of various factors on coating quality of casein. For nearly every positive statement made by one paper-coater relative to casein, there is made a contradictory statement by another. The results of this investigation should a t least be a common basis on which many disputed points may be definitely settled. Most of the commercial caseins gave satisfactory coatings, but in the case of a few the coatings were unsatisfactory as a
August, 1933
1> U L S TH IA L
AND
E N G I N E E 11 I
N G C H E M I S T 11 Y
90;
FIGURE1. DBTK~BUTION OF CASEZNSIN COATINGS
result of the foaming of the slip during applieatioii to the paper. It apparently is not justifiable to claim that lactic casein as a type differs from grain-curd or sulfuric caseins in inherent foaming tendency; either foaming or nonfoaming caseins may result from any of the three general methods of manufacture (compare samples4,9, and 14 with 5 , IO, and 11, respectively). Tlie results of this paper indicate that tendency to cause foam is a property existeut in t,lie dry casein
wlien it is delivered to tlre user. It was practically impossible to prevent foaming in slips from certain caseins-e. g., sample 4; it was practically impossible to cause foaming in slips from certain other caseins-e. g., sample 5. Tlie results indicate that, as to thcir relative value for papercoatink, the Iiydrochloric acid caseins should be placed in the following descending order: 5, 6 , 3,2, 7,4, and 8, the last two both being pnor. A blend of a11 seven was satisfactory. Of
908
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 25. No. 8
the sulfuric acid caseins, sample 10 was satisfactory and 9 was All of the caseins used in the coating work dissolved compoor. There were little, if any, differences among self-sour pletely in the alkalies of the coating mixtures, thus indicating caseins 11,12, and 13; 15 was on the border line; 14 was poor. that caseins of really poor solubility are rare. Results of the The relative ratings given those samples cannot be correlated solubility test do not indicate coating quality. Although with any of the laboratory tests or analyses of Tables I and 11. caseins 4 and 9 are comparatively low in solubility, sample 1 is Except for manifestations of foaming tendency, the conduct of also. the caseins during preparation of the slip gives no definite Adhesive strength is a property of casein that seems to be indication as to the quality of coating to be obtained. generally considered important; yet few users vary the proThe coatings in which the self-sour lactic caseins were used portion of the casein in their slips on a strength basis or pay a were smoother surfaced before being calendered and had a premium for strong casein. Consequently, i t is rather hopehigher finish after calendering than the coatings containing the less to attempt to convince manufacturers that they should caseins made by the other methods. If there was any mottled wash their curd thoroughly in order to obtain strong casein, effect in the finished papers, it was usually in the papeis in especially since they decrease the yield a t the same time. which hydrochloric acid casein was used. The hydrochloric Strength tests and coating quality do not correlate. caseins gave more of a suiface-sizing effect to the papers than Paper coders, as a rule, are much interested in the viscosity did the lactic acid caseins, and the coated papers curled more of their slips for entirely valid reasons and frequently blame in drying and had considerably more rattle. It is doubtful unexpected variations on the casein. It has been tacitly whether the lactic acid caseins had as good adhesive or clay- assumed by many that the viscosity of a casein solution suspending qualities as the caseins of the other two types, but indicated the viscosity of a slip containing this casein. There the adhesiveness was believed sufficient to give coatings satis- was remarkably little variation in the viscosities of the slips factory for nearly all printing requirements. used in this work when the slips were made u p uniformly. I n the printing tests, the experimental coated papers were Slip 5-219 was more viscous than the others because less substituted for the regular stock being printed by the half- water was used. Viscosities of casein solutions brought to aptone process. KO changes were made in the printing piess proximately the same pH value (Table I) differ widely, but or in the inks. The tests showed all the coatings of the com- not in the same way as viscosities of solutions made u p with mercial caseins to be well bound to the body paper and all uniform quantities of alkali (Table 11), and neither set of of them of good printing quality, except those of sample 4 values is indicative of the viscosity of the slip. It is concluded and possibly those of 8, 9, and 14. It is thought that coat- that variations in viscosities of clay-casein slips, in so far as ings from caseins 12, 14, and 15 might “lift” or “pick” when the usual concentrations are concerned, are not traceable to printed; 7 and 11 would be somewhat less likely to “pick.” the caseins. Furthermore, high viscosity of casein solutions The characteristics of the coatings of caseins 18 to 22 are not cannot be correlated with foaming of slips. sufficiently different to warrant a statement that one method of curdling produces a more satisfactory casein than any other. ACKNOWLEDGMEKT The observable differences in these coatings could readily be The authors have been aided b y valuable suggestions and attributed to unobserved factors in the process of nianufacture. While a conclusion that as good a casein can be advice from B. R.Scribner of the Paper Section, Bureau of made by one method of curdling as by another is probably Standards. S. A. Hall and C. S.Trimble of the Bureau of justifiable, it probably is also true that the details of technic Dairy 1ndust.ry made some of the tests and prepared samples are of less importance in making self-sour casein than in of casein. Several members of the Finishing, Processing, and Converting Committee of the Technical Association of the making the other types. Pulp and Paper Industry have made valuable suggestions and The acidity of a casein, expressed as pH, correlates satisfactorily with its alkali requirement as shown by the figures in verified the authors’ judgment on the quality of coated Table I. For practical purposes it gives a relative measure of samples of paper. The cooperation of the Government the amount of alkali required to dissolve the casein and bring Printing Office in making the printing tests on the coated the solution to the alkalinity desired for the coating mixture, papers, which were an important part of the investigation, is as may be seen by comparison of the proper columns in Table I. gratefully acknowledged. The free acid determination, on account of the fading and LITERATURE CITED consequent uncertainty of the end point, gires different results (1) Bell and Gould, J . Dairy Sei., 14, 337 (1931). when made by different persons. Therefore its correlation (2) Carson, Bur. Standards, Tech. P a p e r 328 (1926). with alkali requirement is poor. While it is true that free acid (3) Gould and Whittier, IKD.ESG.CHEM.,24, 791 (1932). and total acid determinations give infoimation that may help (4) Shaw and Bicking, Bur. Standards, Rssearch P a p e r 254 (1930) ; P a p e r Trade J., 92, KO.14, 5 2 (1931). the casein manufacturer to judge the effectiveness of his pre“Casein and Its Industrial Applications,” p. 276, cipitation and washing technic, these values tell nothing of ( 5 ) Sutermeister, Chemical Catalog, 1927. direct interest to the coater that cannot be obtained more (6) I b i d . , p. 279. directly from the determination of alkali requirement or of (7) Watson, IXD. ESG.CHEM.,19, 1272 (1927). PH. R E C E I V E D February 4, 1933. Some of t h e information in this paper was The ash percentage is an index to the effectiveness of the preeented a t a meeting of the American Dairy Science Association, Davis, washing of the casein during manufacture and to its adhesive Calif., July 14 t o 15, 1931; a t a meeting of t h e Technical Association of t h e strength ( 3 ) . Table I shows, furthermore, that the percent- Pulp and Paper Industry, New York, N . Y., February 17 t o 18, 1932; and ages of calcium oxide or of phosphorus pentoxide correlate b t a conference on paper-coating casein, Washington. D . C., J a n u a r y 13, with adhesive strength when only one type of casein is being 1933. considered. The percentage of milk fat in casein in the range covered in TECHNICAL SECTION SICILL4N SULPHUR CONSORTIUM T O this study is not an indication of either the adhesive strength CONTINUE.A bill has been approved providing for the conor the foaming tendency, As much as 2.25 per cent f a t tinued functioning of the Technical Mining Section of the Sulphur Consortium dissolved July, 1932. This section (casein 15) did not cause grease spots on the paper,.and a Sicilian direct its activities toward the technical improvement of casein free from fat (sample 5) did not foam. These facts will sulfur mining methods in Sicily and will be known as the should be remembered when oils are being used to prevent Board for the Improvement of the Sicilian SUI hur Industry (Ente per il Miglioramento dell’Industria S o l d r a Siciliana). foaming.
