Clay-Casein Slips for Paper Coating Causes and Prevention of Foaming 12. 0.WHITUEH,S. 1'. COULD,AND S. A . HALL,Bureau of Dairy Industry, Washinglun, D. C . A search for the causes of founiiiy of casein solutions has shown that the foarning tendency may De caused by sonie unknown cluiracleri.stic of the milk fronk which /lie casein was prepared, by use of too rapid agitation during precipitation of the casein, by m e of temperulures below 95' F. (35' C.) during precipitnlion, or by insugicierat urashing of the curd. Long time of contact with the precipihting acid is a contributing factor at low temperatures. Mixing of eeen u small proportion of a nonfouniing casein with u cnsein of high foaming tendency prevents foaming. Surface tension depressants are
rjSectizre i n preuenting foamirq t j'added during the preparation of tlte slip and in suficient amounts. Iutensity of foaming of slips is affected sligh.tly by auriation in degree of alkalinity. l'he theory is qffered th,at the foaming tendency of casein is dependent on the degree of aggregulion of the caseiu nwlecules. It is reconmiended on the basis of these results that nlanufacturers of casein insure slow agitation and temperatures ut or above 95' F. during precipihtion of the curd, and immediate draining and washing of the curd. The mixing of batches into large lots is also urged.
HE expression "fuaining tendency" is used in tliis that all possible differences were tried, but all theories and paper to connote that characteristic of a fluid by suggestions that seemcd at all promising were tested. virtue of which it ent.raps sniall bubbles of air and liolds O F FOAhllKG TEKDEKCY them tenaciously. The foam niay rise to the surface in part. or it may remain uniformly distributed throughout the liquid, l'lie method iised for comparison of foaming tendencies the bubbles being free to change their relative positions in u-as essentially that described by Richards ( I ) , who kindly the mobile continuous-fluid phase. gave thc aiit,lirirs a detailed account of his technic previous Foaming of clay-casein slips during their appliciltkin to t,o it,s piiblication and aided wit,h a number of suggestions. paper is probably the rnost troublesome iii~iiciiltyexperi- An accoiiut of a sornem41atsimilar method has been puhlislied enced in coinrnercial paper coating. The adrlitioii of de- by Williams (4). The authors used a 110-volt, 60-cycle, pressants of surface t,ension tu a slip that has already issgiin a. c., one-fifteenth horsepower, synchronous motor, mounted to foam has little, if any, beneficial effect; but the fairly wit11 shaft vertical and operating a t a speed of 1800 r. p. rn. eoiiiinon practice of adding depressants during 1m:paration The synchronism and rate of speed of tire niotor were verified of the casein solution appears to decrease or prcvmit foamiiig h y t,he use of a neon lamp connected to the same 60-cycle in many cases. This, hovcver, adds to the cost of the coat,ing current source as the motor. Since the speed was less than process, and it is tlierefore desirable that the cause of foam- that of the motor rised by Richards, it was necessary to vary ing be ' t r a c e d in so far as p o s s i b l e the design of the stirrer in order to and prevention applied nearer tliesource cause sufficient foaming for measureof the difriciilty. ment. The st.irrer used was mounted That the c a u s c of f o a m i n g is ill' inch on the end of a round shaft I,& herent in the casein and not in the clay (6.35 mm.) in d i a m e t e r and 4 inches or alkalies used in the slips, has lieen (10.2 em.) long, and consisted of a blade s u g g e s t e d b y Sutermeister ($) and 1 3/g inches ( 3 . 5 em.) long horizontally, definitely proved hy recently published '/a inch wide vertically, and '/ainch experiments of Shaw and Xickirig (8). (0.8 mm.) thick. Thc siirrer and sliaft It is true that the intensity of foaming vere plated with nickel. may lie increascd by vigorous agitaThe slips were repared, unless othertion, such as is given by the rcciprowise stated, by sogening 11 grams casein cating brushes of the brush coatcr, and in 55ml.wnter, addinx 1.2 rumss soda ash, that it may be affectod to a slight extent IJY change in reaction of the slip, but neither of these influences is the dry clay \VAS sifted through a No.40 sieve prinisl C ' L I I S ~of foaming. previous t,o use. This work has been carried out to One hundred milliliters of the slip were poured into a 100-mi. graduate, and the d e t e r m i n e 11.11 e t h e r t li e Eon rrii ng graduate and its oontrnt,s were weighed. tendency develops in the manufacture Two h u n d r e d grsms of slip were then of casein and how it may be prevented placcd in a 4Wml. low,-form beaker, the or Icssened. The p r o c e d u r e was to motor-driven siirrer placed so that the top of the blade was a/< inch (1.9 cm.) prepare caseins by methods differing below the surface, and the st,irrer run for only in one detail of technic and to 5 minutes. Aftor standing for 1 minute, compare the foaming tendencies of t.he 100 ml. of the slip was poured into t.he FOAMT E ~ ~ E H resulting products. KO claim is made same 100-ml. graduate as hefare, and the 1213
graduate and eontmts were again wpighed. Tlre difference be- iverc prepared with constant rate of addition OS acid for each twoen the weights of 100 ml. before and after stirring is si rnen~ure casein, but with the rates varying widely between samples. of the foaming tendency and is heroin called tho foaming index.
No effect on foaming tendency wns demonstrated. TEMPERATURE IlUltJh'G PRECJPITATIOZ. &!V
