Feb.,
1920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
tion. However, after some experience, t h e worker obtains a concrete understanding of t h e terms “very heavy,” “heavy,” ‘(considerable,” “fair,” and “negligible.” T h e rating is based on one month’s incubation. OBSERVATIONS Contamination Inoculation Other NOMENGrowth Growth Characteristics RATINQ CLATURE Very heavyi , , Tendering of cloth 0 Mildew susceptible Tendering not readily .. .. Very heavy’ observable Heavy1 Marked discoloration Not mildew-reHeavy’ ,, Visible discoloration 3 sistant Considerable Fair Slight discoloration 4 Negligibly mildew-resistant Considerable Nealigible N o visible discoloration 5 Slightly mildew_ resistant Negligible No visible discoloration 6 Considerably milFair dew-resistant NeTligible N o visible discoloration 7 Mildew-resistant Negligible Visible only N o discoloration 8 Highly mildewNegligible through resistant binocular microscope None N o discoloration 9 Very highly milNegligible dew-resistant 10 Mildew-proof No None N o discoloration 1 Where t h e contamination growth is heavy t h e condition of the inoculation growth may be overlooked In fact it is frequently overgrown by the spread of contamination molds.
. . . .. . .. . . . . . . .. . . . .. . . .
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:}
Data permitting the comparison of the results of laboratory tests of t h e mildew resistance of textile fabrics by the above.method with field exposures have been obtained, and, though a t present still meager, are indicative of the value of t h e test. Pieces of treated and untreated cloth were stretched over frames in the form of tents and exposed t o weather conditions in the vicinity of Washington for nearly a year. The samples were then brought into t h e laboratory and examined for mildew. T h e table shows the results of the laboratory test and outdoor exposure of some of t h e samples.
withstand exposure without mildewing is now being determined. The procedure can apparently be relied upon, especially in distinguishing between resistant and nonresistant treatments. SUMMARY
I-The methods heretofore usually employed for testing mildew resistance of fabrics are outlined and their disadvantages pointed out. 11-A laboratory method is described which is simple in execution and t h e details of which have been standardized. 111-A rating on t h e scale of I O and a system of nomenclature have been developed on the basis of laboratory observations. T h e practical significance of these underexposure conditions will be further studied and reported. IV-A comparison has been made of the results of the laboratory test with results of exposure tests.
THE IMFLUENCE OF THE METHOD OF MANUFACTURE ON THE USE OF CASEIN IN GLUE MAKING By Samuel Butterman FOREST PRODUCTS LALJRATORY,MADISON,WISCONSIN Received August 20, 1919
The urgent necessity for a water-resistant glue for use in aircraft construction was realized immediately upon our entry into t h e war, b u t a t t h a t time, in t h i s country, relatively little was known regarding its preparation. The severe weather conditions t o which airplanes are subjected and t h e impracticability of LABORATORY TESTcovering all glued joints in a machine with a waterNUM- Contamination Inoculation Ocher EXPOSURE proof coating, led t h e Air Service of the War DepartBER Growth Growth Characteristics RATING TEST readily observable H e a v i 1y . . . . . . . . N otendering 347911 Very heavy ment and t h e Bureau of Construction and Repair of of cloth 1 mildewed 347921 Heavy . . . . . . . . Marked discoloration 2 Black mil- t h e Navy Department t o adopt very exacting requiredew 347801 Heavy . . . . . . . , Marked discoloration 2 Black and ments as t o water resistance for all glue used in t h e y e l l o w manufacture of certain aircraft parts. The U. S. mildew 34772 Heavy .. . . .... Marked discoloration 2 Black and Forest Products Laboratory, Madison, Wis., was green mildew 34797 Heavy . . . . . . . . Marked discoloration 2 C o n s i d e r - called upon t o investigate this subject in order t o obably miltain definite information as t o t h e properties of, and dewed 34856 Heavy . . . . . . . . Marked discoloration 2 Black milmethods of obtaining water-resistant glue. dew 33309 Considerable Fair Slight discoloration 4 Some black Two types of water-resistant’ glue have been sucmildew 34828 Considerable Fair Slight discoloration 4 H e a v i 1y cessfully developed, one based on soluble blood almildewed 34832 Considerable Fair Slight discoloration 4 Mildewed bumin and the other on casein. Casein is practically 34834 Considerable Fair Slight discoloration 4 Mildewed insoluble in water, but in the presence of alkaline sub32409 Considerable Negligible N o visible discoloration 5 Some black mildew stances i t forms solutions which are highly viscous a n d 34826 Considerable Negligible N o visible discoloration 5 S 1 i. g h t 1 y mildewed possessed of marked mucilaginous properties. If 34748 Considerable Negligible N o visible discoloration 5 Mildewed 33331 Fair Negligible No visible discoloration 6 No mildew lime is present, these solutions soon (‘set,” and on 33460 Fair Negligible N o visible discoloration 6 N o mildew No vjsible discoloration 7 KO mildew 32388 Negligible Negligible drying form a hard mass which does not redissolve in 33434 Negligible Negligible N o visible discoloration 7 No mildew 32383 Negligible Visible only No visible discoloration 8 N o mildew water. Such a mixture of casein, lime and other through alkaline substance, t o which certain other ingredients binocular microscope may be added t o confer additional desirable properties, 33017 Negligible . . , . . . , . NN oo visible discoloration 9 No mildew 33001 None None visible discoloration 10 No mildew forms t h e so-called “waterproof” casein glues which 33003 None None N o visible discoloration 10 No mildew are commercially available a t t h e present time. 1 The first three samples were of untreated gray duck-the remainder were from treated material. I n the early work a t this laboratory in the developI t will be seen from these preliminary results t h a t ment of casein glue formulas i t was found t h a t shipsamples which by t h e laboratory method give a re- ments of casein from different sources, or often two sistance of six or better withstood exposure for a whole shipments from the same maker, exhibited such marked year under normal weather conditions near Wash1 F. L. Browne, “Water-resistant Glues,” Chem. & Met. En&. ai (1919), ington, D. C. How much longer these fabrics will 136.
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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I
differences in behavior t h a t t h e glue formula had t o b e seriously altered for each sample of casein. This made i t necessary t o extend our study t o cover the influence of the method of manufacturing casein on its use in glue. M A N U F A C T U R E OB CASEIN
Casein occurs as t h e principal protein of milk, closely associated with lime a n d calcium phosphate in a form generally designated as calcium caseinate. T h e casein is obtained as a precipitate b y freeing i t more or less completely from this combination. T h e methods of doing this may be divided into two classes: 1-Acidification of milk. The acids commonly used are lactic, hydrochloric, and sulfuric. a-Coagulation of milk by rennet. For the sake of economy, casein is not made from whole milk. The milk is first passed through a cream separator t o obtain butter-fat and t h e skimmed milk is used for the manufacture of casein. Although i t is also possible t o obtain casein from buttermilk, very little is made from i t a t the present time, and we shall therefore confine our discussion t o skim-milk casein. LACTIC ACID OR NATURAL-SOUR METHOD-Ill this method the necessary acidification is produced by the fermentation of the lactose of milk. The milk is allowed to stand a t room temperature until the amount of lactic acid produced is almost enough to cause separation of the curd from the whey, and then warmed to about 130’ F., whereupon the curd separates. The whey is drained off and the curd is sometimes washed with cold water. The curd is wrapped in cloth and pressed to remove the remaining whey or wash-water as far as possible, and dried by spreading it on trays in a drying tunnel through which air, a t a temperature not over 130’ F., circulates. This method of procedure is sometimes spoken of as the “vat” or “cottage cheese” method. In order to avoid loss of time fresh skim milk is sometimes warmed and allowed to flow out of a pipe. From a neighboring vat a stream of warm, sour whey is allowed to flow in such a way that it mixes with the stream of skim milk, and the liquid falls into a third vat from which the whey is finally drained and the curd washed, pressed, and dried as before. An excellent grade of natural-sour casein is made by the “ejector” method developed by the Bureau of Animal Industry. The skim milk (or buttermilk) is allowed to sour until its acidity, as determined by titration with a standard alkali solution, using phenolphthalein as indicator, is 0.8 to o g per cent, expressed as lactic acid. It is then allowed to run out of the tank through an ejector where it is rapidly heated by introducing steam, and to fall into a second tank where the curd collects on top. The whey is drained off and the curd washed, pressed, and dried. METHOD OF COAGULATION WITH ACIDS-In this method the necessary acidification is produced by adding acid directly to the milk. This saves the time required for the production of lactic acid by natural souring. The fresh skim milk is placed in a vat and heated with steam to about 120’ F. About one pint of sulfuric acid (sp. gr. 1.84) for every 1,000lbs. of milk is diluted with a gallon of water and added to the milk, which is gently stirred until the curd separates. The whey is drained off and the curd washed. It may then be pressed and dried, as in the case of natural-sour casein, or it may be “cooked.” This process consists in covering the curd with water and heating to 1 7 0 O to 175 F., when the curd collects in a semi-fluid, plastic, tough mass. The water is drained off, and the soft curd barreled and shipped.
A. 0. Dahlberg, “The Manufacture of Casein from Buttermilk or Skim Milk,” U. S. Dept. of Agr., Bulletin 661. 1
By far the greater part of the commercial casein made in the United States is produced by the sulfuric acid method. In some creameries where the whey is later used for recovering lactose, hydrochloric acid is substituted, to avoid certain mechanical difficulties a t a later point in the process. J. L. Sammis, of the Dairy Department of the University of Wisconsin, has shown that by proper manipulation sulfuric acid curd can be made with as low ash content as natural-sour casein.‘ THE GRAIN-CURD METHOD-The Bureau of Animal Industry has developed a method for making commercial casein by the hydrochloric acid method which gives a product of exceptional purity. This method has been successfully put into practice by a t least one large creamery. The method takes its name from the character of the curd when obtained from milk in which the hydrogen ion concentration is approximately that of the isoelectric point of casein, PR. = 4.6. This is easily controlled in practice by adding the dilute acid to the milk and testing small samples by means of methyl red, comparing the color with that of a stock solution of known hydrogen ion concentration. By the careful regulation of temperature and acidity the curd is easily freed from impurities. METHOD OF COAGULATION WITH RENNET-Rennet casein is obtained by treating milk with rennet. Since no acid is formed during the process, the ash content of the caesin thus produced is very high. C H A R A C T E R OF C O M M E R C I A L C A S E I N
Commercially available caseins are of t h e most diverse character. They range in quality from practically white, sweet smelling products relatively low in impurities, through light yellow t o dark brown material with sour a n d highly offensive odors. T h e marked variation in behavior of caseins in various a p plications is shown by t h e specific preferences of different consumers for one t y p e or another. T h u s one manufacturer maintains t h a t natural-sour casein alone is satisfactory for his purpose, whereas another stipulates t h a t only mineral acid casein is t o be furnished. I n many instances scientific supervision is lacking; no explanation for this preference is given beyond some reason expressed in the vernacular of t h e trade and hence devoid of any significance t o one not familiar with the particular application under consideration. I n our work in developing casein glue formulas, this wide dissimilarity in t h e caseins was a source of much difficulty because a formula which gave satisfactory results with one casein might fail completely with another. With any casein of reasonably good quality, however, i t was possible by an alteration in t h e proportions of t h e ingredients of t h e formula t o obtain a satisfactory glue. Investigations were therefore made into t h e causes of variation in commercial casein made by different methods and their effect upon the use of casein in glue. The results of t h e first part of this work have already been published.2 Over 300 samples of commercial casein, made by different methods a n d different makers, were analyzed for moisture, fat, ash, “acidity,” a n d nitrogen, t h e last giving a measure of the organic impurities other t h a n f a t present. I n Work about to be published. F. I,. Bromne, “The Proximate Analysis of Casein,” THISJOURNAL, 11 (1919), 1019. 1 2
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Feb., 1920-Z
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Table I are given t h e results of t h e analyses of samples of casein made a t a large creamery b y different methods. These results are typical of t h e casein produced at t h e present time b y each of these methods: TABLEI-RESULTS or( ANALYSESOF CASEIN MADE BY DIFFERENT METHODS
NitroZen
Buttermilk 9 6.97 9.56 2.18 0.88 1.36 14.77 9.2 Grain curd 11 9.48 0.33 3.76 1.08 1.65 14.84 9.9 Natural sour 18 7.87 0.27 2.62 1.33 2.16 14.84 8.7 Sulfuric acid 34 7.81 0.35 5.36 3.02 4.05 14.46 7.6 Sulfur i c cooked 8 8.89 0.12 5.58 3.92 4.25 15.04 5.9 Hydrochloric cooked 8 9.44 0.18 5.09 4.14 4.71 15.03 5.2 Hydrochloric acid 6 7.10 0.16 6.03 5.51 5.74 14.32 6.7 Rennet 3 8.29 0.63 8.39 7.18 7.97 14.41 7.9 1 Acidity is expressed as cc. of N/10 sodium hydroxide solution required to dissolve 1 g. of moisture-, fat- and ash-free casein and give a solution neutral t o phenolphthalein.
For skim-milk casein t h e moisture a n d f a t contents are independent of the method of precipitating t h e curd, although t h e nitrogen content varies considerably. None of these seems t o have much influence on t h e behavior of casein i n glue. Further discussion will therefore be limited t o t h e effect of ash content and “acidity.” I N F L U E N C E O F I M P U R I T I E S O N USE O F CASEIN I N G L U E
It was early observed t h a t caseins prepared b y t h e three commercial methods-lactic acid, mineral acid, and rennet-show marked differences with respect t o t h e quantity of water required t o reduce t h e glue prepared from t h e m t o t h e same viscosity. I n general, caseins of t h e same t y p e require a quantity of wat,er which varies within a definite range and is somewhat sharply differentiated from t h e quantity required by other types. Indeed, in most cases,1 i t is possible t o name t h e method of manufacture b y a mere observation of t h e relative amount of water required b y t h e casein under investigation. From Table XI it will be seen t h a t this property closely parallels t h e ash content of t h e casein. Since this variation i n water requirement is b y far t h e most serious one encountered i n using a n y casein for glue making, a thorough study was made of t h e relation between water requirement a n d ash content of commercial caseins. For this purpose casein glue Formula 4 of this laboratory2 was selected, and glues were made from a large number of commercial caseins of different kinds, t h e amount of water used i n each case being varied until t h e desired viscosity was obtained. A similar study was made later with three entirely different glue formulas. T h e results obtained were similar in all cases; therefore t h e d a t a given below seem t o have general application t o casein glues. T h e method of procedure was as follows: I O O t o 2 0 0 g. of dry, powdered casein were weighed and mixed with x parts of water. After soaking a few minutes until t h e casein was thoroughly wet, a suspension of lime containing one p a r t of hydrated lime t o 6 parts of water was stirred in. T h e amount of 1 Caseins made by the method of Sammis or by the grain-curd method are exceptions t o this rule. 2 U.S. Patent 1,291,396, granted to S. Butterman, and assigned t o the United States.
I43
lime used i n this suspension was equivalent t o 15 per cent of t h e weight of casein used. Finally a n amount of sodium silicate solution (sp. gr. 1.4)equal t o 0.7 of t h e weight of casein was added, a n d t h e mixture was then vigorously stirred until all particles of casein h a d dissolved, giving a homogeneous mass. ( I n t h e following tables t h e “water-casein” ratio means t h e ratio of t h e total weight of water used t o t h a t of casein.) Among t h e characteristics observed in these glues were t h e consistency a n d glue “life.” If t h e glue exhibited, b y simple observation, a viscosity intermediate between a thin, watery mixture and a thick, heavy mixture, i t s consistency was recorded a s “medium.” Similarly a very high viscosity was described as “stiff.” By t h e t e r m “life” is meant t h e period of time between t h e preparation of t h e glue a n d t h e point where i t becomes too thick t o spread properly. Seventy-two different caseins were tested in this way. A few typical samples selected a t random are given in Table 11. TABLE11-INFWENCE OF ASH TYPEOF
CASEIN Grain curd Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Sulfuric acid Grain curd Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Rennet
Ash Per cent 1.28 1.43 1.43 1.44 1.49 1.62 1.7 1.81 1.81 2.51 2.62 2.64 2.7 3.02 4.29 4.91 4.96 4.96 4.93 5.06 5.08 5.10 5.36 5.58 6.03 8.59
ACIDITYON VISCOSITYAND LIFE OF GLUE Ratio of Acidity Water t o Life Cc. Casein Consistencv Hrs. Medium ... 2.3 12.0 2.4 Medium 7.4 11.0 2.4 7.6 11.0 Medium 2.4 9.0 Medium 18.0 2.5 Medium 7.9 16.0 8.8 Medium 2.4 8.5 2.3 7.9 Medium 16.0 2.5 8.6 Medium 23.0 2.4 8.5 Medium 12.0 2.5 8.2 Medium 10.0 2.5 Medium 10.6 6.5 Medium 2.5 7.0 14.0 2.5 ... Medium 9.0 Thin 3.0 18.0 9.1 2.7 Medium 6.0 6.5 Stiff 2.7 7.1 5.5 8.1 Medium 2.7 5.0 Stiff 2.7 6.0 6.9 Medium 2.9 8.5 9.0 2.9 ... Medium 6.0 2.9 8.2 Medium $. 6.5 Stiff 3.1 8.4 3.0 Stiff 2.8 5.8 6.0 2.8 Medium $. 5.7 7.0 Stiff 3.1 6.5 4.5 3.7 5.5 Medium 5.0 AND
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+ + +
+
+
An examination of Table I1 will show t h e close relation between t h e ash content of casein and t h e watercasein ratio required t o give a glue of medium consistency. This at once explains the variation in t h e behavior of casein made by different methods. It is t o be noted t h a t when a mineral acid casein is so made t h a t its ash content lies in the same region as lactic acid casein, its water requirement approaches t h a t of t h e latter. It should also be observed t h a t there is no abrupt transition in t h e ash contents, a n d therefore in t h e water-casein ratios, of caseins made by different methods, b u t t h a t they merge gradually into each other. T h e recent work of t h e Bureau of Animal Industry and of J. L. Sammis has shown t h a t , under t h e proper conditions of manufacture, t h e ash content of mineral acid casein is as low as t h a t of lactic acid casein, in which case there is n o difference in t h e behavior of t h e products of t h e two methods. It is interesting t o note, as shown in Table 111, t h e effect on t h e behavior of t h e casein after washing. Washing lowers t h e ash content and consequently the water-casein ratio required t o produce a given
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
I44 TAB&$111-EFFECT TYPEOF
CASEIN Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Lactic acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid Sulfuric acid
OF
WASHING THE CURD ON THE BEHAVIOROF THE CASEIN Ratio of Acidity Water to Life Cc. Casein Consistency Hrs. 8.2 2.5 Medium 10.0 9.0 2.4 Medium18.0 8.5 2.3 Medium 7.5 1.93 7.4 2.4 Medium11.0 2.20 8.9 2.5 Medium 11.0 ~~.~
Times Curd Ash Washed Per cent 0 2.51 3 1.44 0 2.46
3 0
+
5.9
16.0 6.5
10.6 9.0
2 0 Several
4.15 3.94 2.64
13.0
5.7 6.2 6.5 6.3 8 2 7.0
-
2.8 2.6 2.5
Medium Medium MediumMedium Medium-
7.0 12.0 6.5 9.0 9.0 14.0
viscosity. This is shown in t h e table either b y t h e lower water-casein ratio or by t h e lower viscosity or longer life exhibited b y the glues made from t h e lower ash caseins.
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No. z
t o correct roughly t h e water-casein ratio t o conform t o this viscosity wherever i t was not actually observed. Table V illustrates such a correction in t h e case of two glues. TABLE V Ash Per cent
6.03 1.43
Water Casein Observed 3.1
2.40
Consistency Stiff Medium
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-
Water Casein Corrected 3.3
2.2
Consistency Medium Medium
By extrapolation it can be predicted t h a t an ashfree casein would require 1.85 parts of water. A sample of casein, made b y t h e Van Slyke’ method, was available whose ash content was 0.38 per cent. According t o t h e graph such a casein should require 1.95 parts of water t o make a glue of given viscosity. Investigation showed t h a t 2. I 5 parts were actually required, which is well within t h e experimental error. The curve in Fig. I represents an equation of t h e type y = mx
+ c.
Hence if A is the ash content of t h e casein, and W t h e water-casein ratio required t o give a glue of medium viscosity, W = o.24A I.8j2. By making a determination of t h e ash content of a given sample of casein, i t is therefore possible t o tell a t once t h e proper proportion of t h e ingredients required t o mix i t into a satisfactory glue, regardless of t h e method by which t h e casein has been prepared. It is therefore possible t o use casein made b y any of t h e commercial methods for making casein waterresistant glue and still obtain uniform results.
+
FIQ.1 C A S E I N GLUE-CHARACTERISTIC
CURVE
The general relations just discussed are presented in a very striking manner if a casein glue characteristic curve is constructed by plotting ash content against water-casein ratio. I n Fig. I four typical points are plotted-one for each type discussed. The properties of each point have been selected t o represent t h e average characteristics observed for these types. The d a t a used for this curve are given in Table IV. T h e water-casein ratio in each case is such as t o produce a glue of medium viscosity. TABLEI V T Y P B OF
CASEIN Grain curd Lactic acid Mineral acid Rennet
Ash Per cent 1.8
2.5 4.0 8.6
Water Casein
2.3 2.4 2.8 3.9
FIG.2 SUMMARY
I n Fig. 2 t h e values of ash and water-casein ratio necessary t o give a glue of medium viscosity are plotted for 72 different samples of casein. The curve drawn coincides with Fig. I . The average deviation from t h e straight line approaches 0 . 2 part of water. This is practically negligible because t h e water was not measured more closely t h a n 0.1part and t h e observation of viscosity is only approximate, so t h a t t h e experimental error is a t least 0.3 part; yet b u t two of t h e 7 2 points plotted exceed this experimental error. I n checking t h e d a t a of Table I1 against this curve, i t must be remembered t h a t t h e curve is drawn for medium viscosity glues, and therefore i t is necessary
I-A brief description of the commercial methods of manufacturing casein is given. a-The variation in t h e behavior of casein made b y different methods when used in water-resistant glue is due t o t h e variation in ash content. 3-Since t h e amount of water required t o give a glue of medium viscosity is a linear function of t h e ash content, i t is possible t o plot a “glue characteristic curve” for any casein glue formula by means of which a uniform production of glue from casein made b y any of t h e commercial methods can be insured 1
J . Bioi. Chcm., [ l ] 2s (1918).
* These constants apply t o Formula 4 only.
