me ch a n i ca.1 r t:f rig e r a t ion. p r o c e s ses a n d e c! 11 i p men t a r e nom- available a t all t e m p e r a t u r e s , ranging f r o m a fevi degrees allox-e absolute zero t o a few degrees belo117 atmospheric t e m p e r a t u r e , i n great \-ariety of p l a n t s a n d ranges of first a n d operating costs. T h e tendency of t h e d a y is t o produce greater a n d greater variety of appliances. each b e t t e r a d a p t e d t o a special application a n d to correspondingly increase t h e n u m ber of applications. T h e initiative m u s t . h o v e v e r , come f r o m t h e user, a n d t h e user of t h e f u t u r e is t h e chemical m a n u f a c t u r e r w h o must meet t h e refrigerating machine producer half way, so t h a t b y joint effort t h e industries m a y receive m a x i m u m benefit.
C. E. LUCKE ~
~
THE THEORY OF THE PERFECT SHEET ASPHALT SURFACE T h e t h e o r y of 11 perfect sheet a s p h a l t surface is based u p o n a s t u d y of t h e behavior of surfaces a n d films. T h e most m o d e r n conception of t h e chemistry of colloids is likewise based on t h e relation of surfaces a n d films. Colloid chemistry is, therefore, of g r e a t value i n interpreting t h e behavior of such surfaces and i n guiding t o their rational construction. As long ago a s 1 9 0 j t,he n-riter called a t t e n t i o n i n “ T h e M o d e r n -1sphalt P a v e m e n t , ” published i n t h a t year, t o t h e fact t h a t t h e more or less satisfactory or unsatisfactory n a t u r e of a sheet a s p h a l t p a v e m e n t depends o n t h c surface a r e a of t h e particles composing t h e mineral aggregate of s a n d a n d filler entering i n t o i t s construction, t h e a m o u n t of b i t u m e n which m a y be used i n such a mixture, w i t h o u t being present i n excess, being d e p e n d e n t o n t h e e x t e n t of t h e s u b division of t h e aggregate a n d its available surface a r e a t o which b i t u m e n m a y adhere. A t t h a t t i m e he went no f u r t h e r i n t o t h e consideration of a n y effect t h a t t h i s surface a r e a might h a v e upon t h e mixture. W i t h t h e development of t h e m o d e r n conceptions of colloidal or dispersoid chemistry a n d of adsorption which h a v e been f o r m u l a t e d since t h e n , i t is a p p a r e n t t h a t t h e e x t e n t of surface a r e a presented i n a n y mineral aggregate. especially i n connection with t h e presence of colloid material, is of m u c h greater i m p o r t a n c e t h a n h a d previously been appreciated. I n order t o unders t a n d this, one m u s t h a v e some comprehension of t h e principles of physical chemistry a n d . especially, of t h e modern conceptions of colloid material. Colloidal chemistry originated i n t h e investigations of G r a h a m i n t h e sixties of t h e last c e n t u r y . It t h e n l a y d o r m a n t f o r f o r t y years a n d h a s only recently been developed t o a n e x t e n t commensurate with t h e importance which i t is now recognized a s h a v i n g , T h e original idea of G r a h a m was t h a t substances could be classified as crystalline a n d colloidal, with a s h a r p line of division between t h e t w o . according t o whether or n o t t h e y m-ould, i n solution, diffuse t h r o u g h a n a n i m a l or semi-permeable m e m b r a n e . I t is now recognized t h a t colloids a r e merely a s t a t e of m a t t e r , one i n a highly dispersed or subdivided condition. B y a p p r o p r i a t e means, in a suitable medium or phase wiTh which t h e substance does r,ot form a molecular so!urion. cryst:illine substances can be
obtained i n such a degree of subdiL5sion or dispersion t h a t t h e y exist in a colloid s t a t e . i. e . , t h e y will remain suspended i n a medium indefinitely. T h e chemistry of colloid m a t t e r t h e n differs from t h e chemistrl- of m a t t e r i n i t s o r d i n a r y f o r m , merely liy t h e degree of i t s subdix-ision or dispersion. I n order t o be dispersed i n colloid f o r m a substance m u s t exist i n a system of a t least t w o phases: a n interior or disperse one \\-hich m a y be solid or liquid, a n d an exterior or continuous phase i n which i t is dispersed. T h e main characteristic of t h e disperse phase is i t s s t a t e of subdi7-ision or degree of dispersion. Bancroft has characterized t h i s a s fo1lows:l “If we d r o p a stone i n t o water, i t sinks very r a p i d l y ; if we grind t h e stone i n t o coarse particles these sink less r a p i d l y ; if we grind t h e stone i n t o fine particles, these sink slowly; if we grind t h e stone i n t o very fine particles we should expect t h e m t o sink very slov-ly, t h e r a t e being a function of t h e diameter of t h e particles. T h i s is n o t t h e case, howe\-er. Very fine particles do n o t follow Stokes’ e q u a t i o n a n d do not settle a t all, because of t h e Brownian movements which are negligible for coarse particles. We, therefore. conclude t h a t a n y substance can be brought i n t o a s t a t e of colloidal solution provided we m a k e t h e particles of t h a t phase so small t h a t t h e Brownian movements will keep t h e particles suspended, a n d provided we prevent agglomeration of t h e particles b y a suitable surface film.” T h e Brownian motion t o m-hich Bancroft refers is one which c a n be discerned under a n i n s t r u m e n t known a s t h e ultra-microscope which makes visible particles which a r e invisible i n t h e o r d i n a r y i n s t r u m e n t . I t serves a s a means of detecting m a t t e r in a colloid s t a t e which has been unavailable except within t h e last decade. T h e size of particles, when in a colloid s t a t e , is ordinarily a s small or smaller t h a n 0.0001 m m . i n d i a m e t e r , a n d i n t h e case of some solids no larger t h a n 0.000006 m m . A realization of t h e enormous surface a r e a possessed b y disperse solid colloids of t h i s size m a y he arri7-ed a t f r o m t h e f a c t t h a t if a n a m o u n t of material repres e n t e d b y a cube, one side of which h a s a dimension of one centimeter, is reduced b y decimal subdivision only t o t h e coarsest colloidal size, a I O t h o u s a n d t h of a millimeter i n dimension, t h e n u m b e r of cubes produced would be I O t o t h e I j t h power. while t h e surface area would be increased t c ) 60 s q u a r e meters: or I O O , O O O t i m e s t h a t of t h e original cube. T h e great increase i n s u r f a c e a r e a of t h e finer material over t h a t exhibited b y t h e surface a r e a of a single cube is a t once m a d e e v i d e n t , a n d t h e importance of having such a material present in a sheet asphalt surface mixture is a p p a r e n t . if a large surface area is 2necessary f e a t u r e of t h e mineral aggregate of a perfect surface, which: i n t h e light of a c t u a l cxxperience, a p p e a r s t o be t h e case. I t is also of great importance because of t h e surface energy developed t h e r e b y . in addition t o t h e f a c t t h a t t h e large surface area permits t h e us? of ;% greater 1
J . Phys. C h e m . , 18, 549.
T H E J O C R , V A L O F I N D L S T R I A L -4 N D EiYGIAVEERING C H E M I S T R Y
464
a m o u n t of b i t u m e n as a cementing material. Surface energy is well d e m o n s t r a t e d b y t h e fact t h a t if t w o plates of glass, which are g r o u n d perfectly parallel, be brought t o g e t h e r with or without water, i t is difficult t o s e p a r a t e t h e m , owing t o t h e surface energy of t h e film of air or w a t e r which is imposed between t h e m , energy f a r greater t h a n c a n be a t t r i b u t e d , as h a s been asserted, t o t h e pressure of t h e atmosphere. This s a m e p h e n o m e n a is exhibited i n cementing t o g e t h e r with b i t u m e n t h e particles of a mineral aggregate of a sheet asphalt p a v e m e n t , having a g r e a t surface a r e a . Sheet a s p h a l t p a v e m e n t s consisting of a mineral aggregate which contains a large a m o u n t of filler h a v e proved more satisfactory, a n d a r e more durable when constructed with a b i t u m e n containing highly dispersed colloidal m a t t e r . Asphalts containing disperse colloids h a v e given more satisfactory results t h a n those i n which t h e finest particles consist only of a d u s t or filler, n o t i n a colloidal s t a t e , such as ground limes t o n e or P o r t l a n d c e m e n t , a d d e d b y t h e h a n d of m a n , a l t h o u g h t h e addition of such fillers i n large a m o u n t will i m p r o v e t h e character of a surface over one which contains little filler a n d a coarse s a n d . It h a s been recognized for some y e a r s t h a t certain surfaces, which h a v e been c o n s t a n t l y exposed t o heax-y travel. such a s
ing a substance which gives great body a n d density t o t h i s binding material. T h e b i t u m e n i n t h i s case has been shown, however, t o h a v e a f u r t h e r influence i n t h a t i t s e n - e s as a protective colloid or film t o t h e highly dispersed particles. T-arious bitumens seem t o differ i n t h e degree i n which t h e y exercise protective properties a n d a p p a r e n t l y i n accordance with their viscosity or density. T h e i r relative value i n t h e production of a successful sheet a s p h a l t surface seems t o be closely associated with t h i s p r o p e r t y as well as with surface a r e a . T h e large surface a r e a provided b y a material i n a colloidal s t a t e has a n i m p o r t a n t bearing upon t h e stability of a sheet asphalt surface. As long ago as 19oj t h e writer called a t t e n t i o n i n “ T h e 11odern Asp h a l t P a v e m e n t ” published i n t h a t y e a r t o t h e f a c t t h a t t h e surface area of t h e particles composing t h e mineral aggregate, consisting of s a n d a n d filler, i n fluenced or regulated t h e a m o u n t of b i t u m e n which m a y be used in such a mixture without being present i n excess. F o r example t h e figures i n t h e accompanying t a b l e show t h e a r e a of t h e particles calculated i n s q u a r e feet occurring i n a coarse a n d a fine mineral aggregate of t h e t y p e s in use i n New Y o r k i n t h e nineties. T h e
sc‘ M B E R O F P A R T I C L E S A N D THEIRS U R F a C E , P E R P O U K D , I N L f I N E R A L CO.4RSE S A X D AND
M e s h of sieve 10 ~~
20 30 40
50
80 100 200 0 . 0 0 5 mm.
Per cent 13 12 10 13 27
100
No. of oarticles 12,592 66,186 167.547 664,250 5,021,870 4,086,220 10,415,700 31,924,300 i 6 .,6 7 1 ..4 0 0 129,030,065
Surface S o . it. ,958 1.579 1.901 3.593 11.479 5.527 5.952 6.909 6.480
ATES AGGREG
FINES A N D A N D DUST
DLW
No. of Darticles 3,674 38,808 150,796 561,866 4,835,870 6,127,910 22,319,400 44,694,000 153.343.000
Surface Sa. ft. 0.295 0.921 1.715 3.033 11.054 8.099 12.754 9.672 12.960
232,075,324
60.503
Per cent 4
7 9 11 26 15 15 7 6
___
-
44.378
100
t h a t laid o n F i f t h Avenue, New Y o r k , i n 1896-9;. a n d o n t h e Victoria E m b a n k m e n t i n London, h a v e been extremely durable u n d e r t r y i n g conditions. F r o m a s t u d y of t h e s u b j e c t , from t h e point of xyiew of t h e chemistry of colloids, i t c a n now be appreciated w h y t h i s h a s been t h e case, a n d i t opens u p a new line for t h e rational construction of s u c h surfaces i n t h e f u t u r e . An explanation of t h i s now seems possible. Adsorption is t h e power a solid or liquid surface has of holding t h e r e o n a t h i n film of solids, liquids or gases, a n example of which is t h e film of air or w a t e r which is f o u n d u n d e r o r d i n a r y conditions on t h e surface of glass. Colloids possess t h i s p r o p e r t y t o a high degree, owing t o t h e large surface a r e a t h e y present. Adsorption is well illustrated b y t h e m a n n e r i n which a d y e or coloring m a t t e r is removed f r o m i t s solutions b y a s u b s t a n c e like charcoal or kaolin: t h i s is known as selective adsorption. Selective adsorption is of i m p o r t a n c e i n connection with t h e sheet asphalt paving i n d u s t r y because of t h e f a c t t h a t t h e surface of t h e mineral aggregate m a y adsorb selectively a n d hold with g r e a t power certain bitumens or portions thereof which a r e used as binding materials. I n one n a t i v e a s p h a l t i n particular t h e r e is a considerable a m o u n t of mineral m a t t e r n a t u r a l l y present i n a disperse solid colloid f o r m , which shows great c a p a c i t y for adsorption, selecting t h e denser portions of t h e b i t u m e n a n d f o r m -
1’01. 7 , S O .6
-
O F THE
TYPEI N USE IN XEWYORKI N THE KINEIYES DUSTOR FILLER
Size of particles Millimeters 0.08 0.05 0.025
Per cent 18.8 17.17 51.3 5.0 7.2
0 . 0075
0.0025
No. of particles 120,035,300 452,300,200 io,732,900,000
30,7i5,i30,000 1,50,634,400,000
Surface sq. it. 25.976 38.231 226. 825 58.590 178.199
~
io0.o O r , if all t h e d u s t IS of 0 . 0 2 5 m m . in diameter
192,715,475,500
527.821
20,922,050,000
442.157
c o n t r a s t is striking. Another calculation shows t h e n u m b e r of s q u a r e feet of surface i n a p o u n d of d u s t or filler i n use a t t h a t t i m e which m a y be compared with t h e figures for t h e entire mineral aggregate. F r o m t h e d a t a given i t appears t h a t t h e finer aggreg a t e presents a surface area of 6 0 . 5 s q u a r e feet t o t h e p o u n d a n d t h e coarser one b u t 44.4, a difference of 32.6 per cent i n favor of t h e finer material. T h e enormous increase in a r e a , t h e finer t h e material grows, is d e m o n s t r a t e d b y t h e figures given i n t h e last section of t h e table. I n 190j t h e writer went n o f a r t h e r i n t o t h e considerat i o n of t h e effect t o which t h e e x t e n t of surface a r e a m i g h t h a v e upon t h e mixture other t h a n i n providing for a n increased a m o u n t of b i t u m e n , b u t with t h e development of our m o d e r n conceptions of t h e colloidal s t a t e a n d of adsorption, i t is a p p a r e n t t h a t t h e e x t e n t of surface area presented i n a n y mineral aggregate is of m u c h greater i m p o r t a n c e t h a n h a d been previously appreciated. TTe now u n d e r s t a n d t h e f a c t t h a t a n extended surface a r e a i n addition t o providing for t h e use of a larger a m o u n t of b i t u m e n exercises a still more i m p o r t a n t function, d u e t o t h e greater surface energy developed b y t h e large surface a r e a of a fine mixture over t h a t of a coarse one a n d t h a t . aside f r o m t h e greater surface presented b y a fine s a n d as comp a r e d t o a coarse one, t h e presence of highly dispersed
J u n e . 191j
T H E JO17RS.iL OF ISD17STRI:IL
colloids v,Tith their extensil-e surface is necessary for t h e production of t h e most satisfactory surface. There is one other consideration of a physical n a t u r e in connection \Tit11 t h e relation of surface area t o t h e films of bitumen a n d this is. t h e thickness of t h e film of t h e melted b i t u m e n which \Till adhere t o or be sdsor1jt.d b y t h e surface with which i t is brought in contact. dependent i n ' o n e direction on t h e n a t u r e of t h e surface a n d in t h e other o n t h e character of t h e b i t u m e n . I t is known t h a t t h e thickness of adsorbed aqueous films on various surfaces is quite difYerent. The same dilierences have been observed as regards t h e !iehavior of surfaces n-ith different bitumens. T h e more \-iscous t h e bitumen a n d t h e larger t h e a m o u n t of rnlloici material which i t contains, t h e thicker t h e film :in$, consequently. t h e greater t h e cementing pon-er of t h e bitumens which forms t h e thicker film. T h e writer's premise. a t t h e beginning of this paper. t h a t the basis for t h e constriiction of a perfect asphalt surface lies in :i considerxt,ion of the chemistry of surface; a n d films seems. therefore. t o be confirmed a n d t o offer a solution of t h e rational construction of such surf:t ces. CLIFFo R D RICHA R D s o s \~C)OLIVORTH B I - I L D I X ~ ; S E W TORK .
~~~
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T H E EFFECT OF T H E W A R O N ABSTRACTS l h e reduction i n t h e bulk of current c h e m i c d literature due t o t h e war in Europe is reflected in t h e size of t h e recent n u m b e r s of C h e m i c a l A b s l r a c t s . Since a little more t h a n tn-o-thirds of t h e chemical research work reported during t h e past ten years was done in t h e countries now a t war, a considerable effect was t o b e expected. T h e extent of this reduction is shown by t h e follon-ing figures: T h e first six numbers of t h e 1914 1-olunie of Chciiiical A b s t r a c t s contain 5 2 8 6 a b stracts of journal articles; t h e corresponding numbers of t h e present year contain h u t 3 4 3 j such abstracts. This ihon-s a decrease of a b o u t 3 j per cent. T h e effect o n t h e p a t e n t literature has n o t been so g r e a t ; there has Leen a decrease of a b o u t 2 0 per cent: the n u m b e r of p a t e n t a b s t r a c t s appearing in C i i e w i c a l .-I hstracts in t h e first six n u m l ~ c r sof Volume 8 being 2 2 0 1 a n d in t h e corresponding n u m b e r s of Volume 9 , 1 7 j j. T h e numhers of pages in C h e m i c a l A b s t r a c t s for t h e t w o periods are. respectively, I 2 2 0 a n d 8 7 2 ; t h e decrease has been z 8 . j per cent. T h e tn7o periods are only approximately comparable because, since t h e beginning of t h e war. irregularities in t h e receipt of foreign journals in t h e United States have caused delays in t h e publication of a b s t r a c t s in some cases: however. t h e first three m o n t h s of 191; is a more suitable period for t h i s comparison t h a n t h e m o n t h s of 1914 following t h e outbreak of t h e *\lthough there have been delays t h e field h a s been covered 1-ery nearly, if n o t , a s completely as under normal conditions. Practically all of t h e foreign journals t h a t are being published a r e now being abstracted in good t i m e . T h e decrease in t h e n u m b e r of a b s t r a c t s is d u e t o t h e decreased size of t h e journals of t h e warring countries, t h e doubling u p of n u m b e r s a n d t h e fact t h a t t h e publication of some journals h a s been discontinued, a t least temporarily.
T h e chemical journals t h a t ha\-e been discontinued since t h e o u t b r e a k of t h e TTar are few in n u m b e r . T h e papers being published in t h e warring countries are in some cases below t h e normal s t a n d a r d of' q u a l i t y ; nevertheless a considerahle n u m h c r of i.mportant papers is appearing. Surprise has been expressed t h a t t h e reduction i n number h a s n o t been greater. There has been no interruption in t h e receipt in this c o u n t r y of English chemical journals. With t h e exception of t h e abstract sections of t h e Jotiriial of t h e C h e m i c a l S o c i e t y of L o n d o n a n d t h e Jozrrnal of tire S o c i e t y of C h e m i c a l I n d u s t r y a n d a slight decrease in size. t h e English journals show h u t little effect of t h e n-:Lr. There ha\-e been delays a n d irregularities in t h e receipt of German journals b u t almost all of t h e m are being published a n d are now reaching t h e United States m-ith sonic degree of promptness if obtained directly from t h e publisher. J n m a n y cases t w o or more numbers of t h e German journals are appearing hound together as one normal-sized number. Several of t h e French journals have been discontinued b u t t h e more i m p o r t a n t ones chemically are appearing. T h e n u m b e r of papers published in t h e m during t h e first three months of 1 9 1 j . while small, is greater t h a n t h e number appearing during t h e last, three months of 1914. T h e JouYTzal of tire R u s s i a i r P h y s i c a l Ckeitiiral S o c i e t y is t h e only i m p o r t a n t Russian chemical journal. T h e J a n u a r y , I ~j ,In u m b e r of this journal I\-as receivetl -\pril 1 0 t h ; e\Tery effort t o obtain or locate t h e 1914 n u m b e r s published since t h e o u t b r e a k of t h e war met with failure until I I a y 3 r d . at which time all were received i n one bundle. S o decrease i n size is shonm. -1 full-sized number of Rccrieil d e s t r a o o ilx c l i i m i q u e s des P a y s - B a s ct d e la Brlgiqire was pu1,lishecl in January. This is a very i m p o r t a n t period for Ciiewric-ai d bsfracts. These are troublesome d a y s for a n abstract journal n-hich endeavors t o report completely' a n d promptly t h e progress of chemistry throughout t h e x o r l d ; however. t h e handicap t o Chevzicul .lbstrnrts is less t h a n t h a t experienced b y t h e other chemical abstract journals of t h e world. Clzeiizical .Ibsfracts mill be t h e only complete record of t h e chemical researches rcported during t h e war period. T h e J a n u a r y , F e b r u a r y a n d M a r c h n u m b e r s of t h e J o t t r i i a l o,f tire C:/ientical S o c i e t y of Loizdoii, which correspond t o t h e period being used for comparison. do not contain a single abstract of a German paper published since t h e outbreak of t h e war. T h e Jourizal o j t h e S o c i e t y of C h e m i c a l I i i d z i s f r y has published during this period abstracts for only n small n u m b e r of t h e papers t h a t have appeared in t h e G e r m a n journals. T h e numbers of C h e n i i s c h e s Z e n trcziblatt for t h e period ( t w o not available for checking a t t i m e of writing) contain a n u m b e r of references t o English journals, b u t t h e y are n o t covered completely; no references t o French, Russian or Japanese journals are t o b e found. Cnless t h e mails from t h e warring countries are i n t e r r u p t e d , Chemical d bstracts c a n be relied on t o continue t o cover t h e field completely a n d i n most cases as p r o m p t l y as delays in t h e receipt of journals will permit. E. J . C R A N E
