September, 1926
IiVDli;STRI-kL .41\;'D ENGINEERING CHEMISTRY
965
Traffic Paint' By H. A. Nelson and S. Werthan THE NEW J E R S E Y Z I N C
CO., PALMERTON, P.4.
high hiding power makes an paint is fed between a roll ideal combination from a n made up of steel disks and a Quantities of paint are being used for marking traffic economy point of view. I n s e c t i o n a l steel edge that lines and directions on streets and highways. This this paint the consistency, maintains contact with the paper covers the results of a study of the proper formuspreading rate, and opacity road surface. The feeding lating and suitable for the testing of this type will be so balanced that of the paint, then, is threeof paint. when the mafold-between the disks, bt,The properties of paints designed for this purpose, c h i n e is being used most tween the sectionaledge and considered in or less detail, are consistency, drye f f i c i e n t l y just sufficient t h e d i s k s , a n d by being ing, hiding power (opacity), color and color retention, paint will be applied to give carried over on the circumvisibility (day and night), and durability (resistance to c o m p l e t e hiding. These ference of the disks. About weather and abrasion). properties depend primarily the only requirements are on the proper formulating that the Daint shall be light of the paint. enough td flow readily i n d that the pigment must not be coarse enough to clog the Color and Color Retention apparatus. The Pfund tintometer can be used satisfactorily for measThe usual laboratory methods for measuring consistencies may be of little value since, owing to the coarse pigmelit, uring the color and the brightness of the paint. As the instruments measuring the rate of flow through a small orifice hiding power and brightness of a paint are directly related, cannot be used and the other types, such as the MacLIichael, they should be considered together. White is the usual and apparently the most acceptable could furnish no information as to the possible dogging tendency of the coarse particles. which is quite important from color for this type of paint, although there are a few colored a practical standpoint. Kext to an actual application test. (yellow and orange) traffic paints on the market. According a screen test should prove the most valuable. The maximum to the writers' tests (Table V, Paint A, and Figure 3, Photoamount and size of the coarse pigment permissible could read- graph 8) these colored paints have lower visibility, besides ily be determined for any particular type of apparatus and showing greater tendency t o discolor, a suitable specification drawn. The limits for maxiinuni Any of the various opaque white base pigments-lead, particle size are also important from considerations of visi- zinc, titanium or lithopone-can be used in traffic paints. bility, abrasion resistance, etc., as will be indicated later. Pigments containing lead are not entirely satisfactory because of a tendency to discolor, apparently due to reaction Drying with sulfur present in vulcanized rubber (Table V, Paints 71, The usual requirements are that the paint shall dry suffi- 72, 7 5 , and 76, and Figure 3, Photograph 5 ) , and possibly ciently within one-half hour after application so that there also to sulfide sulfur from street refuse. The lithopone used will be 110 pick-up under traffic, and thoroughlv dry. free from must be a good light-resistant grade; otherwise a paint conany tackiness, within one hour after application. Tempera- taining it will turn gray. ture and humidity are the important factors to be considVisibility-Day and Night ered in drying and should be included in any ipecification covering drying requirements. By day visibility is meant the visibility of a surface when illuminated by light normal to the surface, such as daylight Opacity or Hiding Power or satisfactory street lights, and viewed a t a large angle of Relative hiding powers of the wet paints, in terms of square reflection. The visibility of the painted surface under these feet per gallon, may be determined by the improved Pfund conditions depends primarily on the relative brightness and cryptometer.* One weakness of this method is that it does the nature of the paint film. A bright, white flat paint furnot take into consideration relative increases in the hiding nishes the highest day visibility. 'Presented before the meeting of the Section of Paint and Varnish Night visibility is considered the visibility of a surface Chemistry of the American Chemical Society, Madison, Wis., May 27 to when illuminated at a large angle of incidence (as by a n 29, 1926. automobile headlight) and viewed a t a large angle of re2 Pfund, J. Frnnklin I n s f , 196, 69 (1923).
Vol. 18, KO. 9
I - D C S T R I A L AND ENGISEERISG CHEMISTRY
966
flection (as from the driver's seat of the same automobile). These two conditions are the most difficult that may be imposed on a reflecting surface. Experience with traffic paints has shown that there is little relation between day visibility and night visibility. This was first drawn to the writers' attention by H. S. Mattimore and M. H. Ulman, of the State Department of Highways of Pennsylvania. I t had been noted, while testing a number of paints submitted for use on the state roads, that some which appeared excellent during the day were practically invisible to a driver approaching on a dark road that was illuminated only by the lights of the automobile. It was to assist the Department of Highways in examining traffic paints for this property that an instrument for measuring visibility was designed in this laboratory by G. F. A. Stutz. Measurements made on a number of motor vehicles indicate that the average height of the headlights above the road is about 35 inches, while the height of the driver's eye above the road is about 60 inches. Assuming the reflecting surface t o be 150 feet ahead of the car, the angle of incidence is 88 degrees 53 minutes, while the angle of reflection is 88 degrees 6 minutes. If the reflecting surface is assumed to be 100 feet ahead, the angle of incidence becomes 88 degrees 20 minutes and the angle of reflection becomes 87 degrees 8 minutes. The latter condition is realized in the instrument illustrated in Figure 1. To determine the visibility, the paint is flowed on a glass plate (4 by 8 inches) and allowed t o dry. To simulate daylight conditions the painted surface is illuminated by the 100-watt frosted electric light, while for night visibility illumination is by the Bausch 8: Lomb Tungsarc lamp. I n either case the light reflection of the painted surface is read by means of a Macbeth illuminometer. A standard plate having a constant coefficient of reflection can be prepared by grinding the surface of a piece of milk glass (4 by 8 inches) with number 80 carborundum grains.
The coefficient of diffuse reflection of the standard used in this laboratory is 77 per cent. I n using the instrument in this laboratory the current through the illuminometer lamp is adjusted so that the fields match when the photometer reading is 2 . The photometer readings are a direct measure of the intensity of the light from each surface. The instrument was first used in the examination of several samples of traffic paints submitted by the Pennsylvania State Department of Highways (Table I). It will be noted that the night visibility readings show the same order as the rating given by the Highway Department. The range between a poor paint and a good one is quite large, permitting a high degree of accuracy in the determination. Kight visibility is a function of the roughness of the surface. The more irregularities there are to turn the light back in its path, the greater will be the night visibility. Therefore, a grooved or corrugated surface, with the grooves perpendicular to the direction of the beam of light, will furnish the highest night visibility. Ratings of Commercial Traffic Paints Visibility READINGON INSTRUMENT Vertical rating given Horizontal by Highway illumination illumination Department (Night visibility) (Day visibility) 2 13.7 Pbbr 1.3 9.0 Fair 3.2 10.7 Good 6.8 11.7 12.5 Good 7.1
Table I-Visibility Identification No. Standard plate M 21.5 >I 1276 hl 1278 AI 2186
It was determined through the examination of the paints of satisfactory night visibility that this property is due t o coarse inert pigment in the paint. To obtain a paint with good color, brightness, and opacity, good pigment suspension, proper consistency for application, and reasonable resistance t o abrasion, that coarse inert should be chosen which can be used in the smallest proportions and still obtain a paint with satisfactory visibility. Since paint containing yery large particles mill settle, clog up the mechanical distributor, and
I
I
Figure 1-Plan
of Apparatus for Measuring Relative Day a n d Night Visibilities
I
I S D C S T R I A L A S D E-YGIXEERISG CHEMISTRY
September, 1926
have poor resistance to abrasion, it is desirable to use as fine inert as is practicable. Paints were prepared using various white inert pigmentsbarytes, limestone, silica, and talc or a s b e s t i n e l o determine the relative desirability and the optimum amount and size of the coarse particles. Light-resistant lithopone n-as used as the white pigment and the vehicle and pigment-vehicle ratio were the same in all the paints. Because of its high specific gravity, barytes settles rapidly in a paint of this type and is not so satisfactory as the lighter inerts. The tests with whiting were satisfactory in all respects except as to durability. The best results n-ere obtained with talc (asbestine) and silica (china clay and gypsum were not tested). Since a fibrous talc remains in suspension somewhat better, it may be preferable to silica. The tests showed that excessive settling of the coarse pigment occurs when the particles exceed 420 microns (too large to pass a S o . 40 screen) and that when they all are smaller than 150 microns (pass a S o . 100 screen) the night visibility of the paint is not good. ;in ordinary building sand was separated into various sizes. and paints were prepared using 70 per cent pigment, of which 60 per cent was lithopone and 40 per cent sand. In Table I1 are given the night visibilities of the paints. According to these data an inert consisting of particles ranging from 500 to 300 microns (through So. 35 on S o . 48 screen) is the most suitable. The very coarse sizes, although producing excellent night visibility, were impracticable becauqe of settling. clogging of the applying apparatus, and lack of durability. Even particles from 500 to 300 microns may cauae trouble when using niechanical methods for applying the paint.
967
paint contained 70 per cent pigment, consisting of a lightresistant lithopone and the inert. The results of this experiment are given in Table IV.
a
Table IV-Visibilities
Inert Silica
of Traffic P a i n t s Containing Various Percenta g e s of Different Inerts Size of Per cent
inert pdrticles Microns 250 to 180
of total Disment . 10
-\'ISIBILITY--
Night
Day
20 30 40 50
9.0 9.8 10.5 9.4 8.5
12.3 12.5 12.5 11.5 11.5
Talc
250
t o 180
10 20 30 40
6.4 9.1 9.0 8.4
11.5 12.0 11.5 11.5
Talc
180 to 150
10 20 30 40
5 4
11.5
8 4 8 8
7.6
12.0 12.5 12 0
A paint with good day and night visibility will be obtained if approximately 30 per cent of the pigment is a coarse inert. The finer material, that is, from 180 to 150 microns is preferable, because of improved physical properties of the paint. An inert of this size is not a commercial product a t present, but satisfactory results were obtained with a special commercial inert. Less than 5 per cent (by weight) of the particles of this inert exceeded 250 microns in size and over 70 per cent were larger than I50 microns. Considering all the properties of the paint, most satisfactory result-b were obtained with a fibrous talc or asbestine.
Table 11-Effect of Inert Particle Size o n Night Visibility of Traffic P a i n t Pize of sand particles Xicrons Night vi4ibility 1.5. & -7.380 (8)to 2000 ( 10)" 2000 to 8-1-0 ( 20) 13.8 10.7 b40 to 590 ( 28) 590 300 :TO0
to to to
500 ( 3.5) 300 ( 48) 210 i 6 5 )
210 to 150 (iooj Figures in parenthesis are screen numbers
IO,'? 11 & 8.2 6 .0
Tests were made using three different sizes of various iiierts : 420 to 250 microns (through S o . 40 on S o . 60 screen). 250 to 180 microns (through S o . 60 on S o . 80 screen), and IS0 to 150 microns (through S o . 80 on S o . 100 screen). The coarse inert is 30 per cent of the pigment, the remainder beinglithopone. The results are given in Table 111. Table 111--Visibilities of Traffic Paints Containing Various Sizes of Different Inerts Size of -----VISIBILITY---inert particlesa Night Day Tolc S o , 1 A 12.2 11.5 B 9.0 11.5 C 8.4 12.5 T a l c -\-o. 2 .1 14 5 11.8 B 10.5 12.3 C 10.1 12.5 Talc X o . 3 A 14.5 12.0 €3
c
10.5 8.8
12.3 12.5
Limestone A
B
c
10.5 8.6 8.0
12 0 11.5 12.0
Silicn A B
11.5 9.6
12.5 12.5
C 9.0 13.0 a A , from 420 to 2.50 microns; B, from 250 t o 180 microns; C, from 180 to 150 microns.
Paints were also prepared using varying percentages of inert. In all the paints the same vehicle was used and the
Figure 2-Abrasion Machine Showing Removable Blocks a n d Rubber Abrasion Strips
Concrete
The relative merits of the different white pigments in combination with inert were investigated: basic carbonate of lead, basic sublimed lead, zinc oxide. titanium pigment, lithopone, and conibinations of zinc oxide and the other pigments being used. Using equal percentages of the same inert. the night visibilities of the original paint films were satisfactory and practically the same with the different pigments. Various vehicles were tested as to their effect on visibility. With the same pigment mixture, vehicles that dry flat result in higher visibility than those that dry with a high gloss. I n certain cases, quch as where the paint is used for marking traffic zones or parking spaces on well-illuminated city streets, night visibility is a niinor consideration. For such purposes any inerts incorporated in the paint could be the ordinary materials. Durability-Resistance
to Weathering and Abrasion
Traffic paints are subject t o severe abrasion as well as very severe weathering conditions on account of their exposed position in service. Ordinarily, the effect of abrasion is
968
INDUSTRIAL AND ENGINEERISG CHEMISTRY
probably more important, and yet the resistance to ordinary weathering must contribute in one way or another to the resistance to abrasion. For example, a paint that chalks or checks rapidly when exposed b light, moisture, freezing temperatures, etc., could hardly be expected to wear well even if the unweathered film shows superior resistance in an abrasion test. True conclusions as to actual durability can be
I-Unexposed, painted test block 2-Paint 67 after test (Table V) 3-Paint 27 after test (Table V) represents typical satisfactory durability
4-Paint 5-Paint 6-Paint
Vol. 18, No. 9
sures-that is, followed light, moisture, and refrigeration exposures in turn. By using this combination of accelerated weathering and abrasion exposure, sufficient deterioration resulted within one week to furnish the desired information, If started at different times more than one set of blocks can be tested, thus increasing the capacity of the equipment. The paints are examined daily during a test and records kept
70 (Table V) 72 74
7-Commercial 8-Commercial 9-Commercial
paint B (Table V) paint A paint C
Figure 3
arrived a t only by testing for resistance to both weather and of the rate of deterioration, which includes chalking, checking, cracking, chipping or peeling, the tearing out of insecurely abrasion. To duplicate the abrasion due to t’raffic,the writers used a anchored particles, darkening, and discoloration. Mr. modification of an abrasion machine that has been widely Stuta’s apparatus for measuring visibility could be modified used for determining the abrasion resistance of r ~ b b e r . ~to accommodate the concrete test blocks, and a record made The abrasion track is made up of eight removable sections, of the changes in visibility in service. A large number of paints Fere given this accelerated exthe surfaces of which are typical of an average concrete road. Figure 2 shows the abrasion apparatus complete with the posure. The results were valuable in determining the effect removable blocks in place. The rubber abrading strips are of various constituents on the life of the paint. Table V repeatedly raised and dropped by lifts, according to a scheme and Figure 3 show the results on typical paints. There has recently developed by the Rubber Section of this laboratory, been no opportunity to make comparative road tests on all thus more nearly simulating the rotating and bounding action the paints tested by the accelerated scheme, but results of of a tire on theroad. (In a more recent modification of this tests on a series of samples submitted about a year ago apparatus, these lifts are made to shift their positions so that, by the Pennsylvania State Highway Department were in relno one spot on the track is hit repeat’edly.) The brushes atire accord with the results of their road tests on the same and suction apparatus ordinarily used on t’heabrasion machine paints. According t o present standards for this type of paint, relawere removed, as the presence of the dust due to the abrasion would be typical of ordinary road conditions. With this tively low cost and high-grade product are not at all incomapparatus comparative tests were made on eight traffic patible. Usually the maximum life now expected or realized in service is six months to a year. The vehicle of a traffic paints a t the same time. An accelerated exposure cycle4 was used based on the cli- paint should dry to an elastic and durable film, which will matic conditions of this locality (Palmerton, Pa.). It was not darken under service and decrease the visibility of the difficult to determine the relative amount of abrasion to add paint. Since quick drying is necessary, a high volatile cont o the regular cycle as there are such marked variations in tent is to be expected. A China wood oil-ester gum or limed traffic conditions. A daily abrasion exposure of approxi- rosin varnish alone or in combination with some linseed oil mately 10 minutes (300 revolutions of t.he track) was finally or other varnish is a very satisfactory vehicle. Appreciable selected as a standard. The cycle was so arranged that this percentages of lead pigments are not favored, because of their exposure a.lternately followed the different weather expo- tendency to discolor. The other white base pigments are suitable and all gave satisfactory results. Any selection will 8 India Rubber World, 61, 357 (1923). have to be based on economic considerations. The addition Proc. A m . SOC.Testing Materials, 24, Pt. I1 (1922); 24, Pt. I1 (1924); of zinc oxide will increase the durability of paints made with 46 (1926) ; Gardner, “Physical and Chemical Examination of Paints, etc.;” the other white pigments. 1926, p. 71; Drugs, Oils & Paints, 41, 265 (1926); Can. Chem. M c f . , 1946.
September, 1926
INDUSTRIAL A,YD ENGINEERING CHEMISTRY
969
Acknowledgment Mattimore and M. H. Ulman, of the Pennsylvania State The authors wish to acknowledge previous work done on Department of Highways, as well as the assistance of G. F. A. fhis subject by W. A. McKim and the cofiperation of H. S. Stut,z and other members of this research organization. T a b l e V - C o m p o s i t i o n , H i d i n g Power, Visibility, and E n d u r a n c e of T y p i c a l Traffic Paints Vchide: Linseed and China wood oil, damar, and ester gum varnish, containing 7 0 per cent volatile, except for sample 64, Jimed rosin-China wood oil varnish (20-gallon varnish), containing 70 per cent volatilt., and sample 67, ester gum-China wood oil varnish (20-gallon v a r n ~ s h ) ,containing 70 per cent volatile -HIDING POWER^Computed a t 80% PigmentBright- Relative brightness Effect of Combined Acness Sq. ft./ Sq. ft./ -VISIBILITYcelerated Weathering vehicle Size of inert particles Paint ratio --PizrnentMicrons Per cent gal. gal. Night Day and Abrasion Test 28
70:30
Lithopone Silica
80 % 20%
590 to 150
90.8
342
636
7.5
13.0
27
70:30
Lithopone Talc
80 % 20 %
590 t o 150
87.0
375
523
8,4
12.5
39
70:30
Lithopone Silica.
60%
420 to 180
80.2
350
354
9 4
11,s
70:30
Lithopone Talc
60% 40%
180 to 150
84.1
366
456
8.8
12 0
45
70:30
Lithopone R hiting
70 % 30%
230 to 180
85.2
394
532
8.6
11 5
64
70:30
Lithapone Talc
70% 30 %
81.8
366
403
11.5
12.3
67
70:30
Lithopone Talc
70 % 30%
82.1
384
429
10.3
12,7
62
70:30
Lithopone Talc
70% 30%
86.0
327
467
12.0
12.2
70
62:38
“ X X ” zinc oxide Talc
83.0
313
368
12.0
11.8
69
66:34
Titanium pigment 707, Talc 30 %
85.2
366
495
11.5
12.5
71
76:24
B. C. R’. I,.
70 % 30 %
79.8
256
253
11.5
11.8
Talc
55
40%
Remainder of samples 707“ between 420 .md 150 307, finer than I50
72
73:27
B.S. L Talc
70 7 30%
78.6
240
221
9 .O
11.5
73
67:33
“SX’”zinc oxide
217, 49% 30%
84.1
366
461
11.8
13.0
“ X X ” zinc oxide 21% Titanium pigment 49% Talc 30 %
87.0
Lithopone Talc
74
65335
390
538
9,5
13.0
Very slight chalking: no cracking or peeling; considerable breaking away of coarse particles: otherwise good resistance t o abrasion Slight chalking: no cracking or peeling: considerable breaking away of coarse particles: otherwise good resistance t o abrasion Very slight chalking: considerable cracking and peeling; resistance to abrasion poor Very slight chalking: no crackine b- -u-t slirht --peeling on one side; no breaking away of coarse particles and good resistance to abrasion Very heavy chalking: bad cracking and peeling; no breaking away of coarse particles b u t flaking off; very poor resistance to abrasion
--
Very slight chalking; no cracking b u t peeling along edge of panel; no breaking away of coarse particles; fair resistance t o abrasion Very slight chalking; considerable cracking and peeling: no breaking away of coarse particles; fair resistance t o abrasion Slight chalking; no cracking; considerable peeling; no breaking away of coarse particles: fair resistance t o abrasion No chalking: no cracking or peeling; no breaking away of coarse particles; good resistance t o abrasion Considerable chalking; no cracking or peeling; no breaking away of coarse particles: good resistance to abrasion Considerable chalking; no cracking or peeling: no breaking away of coarse particles; fair resistance to abrasion. The paint showed a yellow discoloration Considerable chalking; no cracking or peeling; n o hreaking away of coarse particles; good resistance to abrasion. The paint showed a brown discoloration Moderate chalkinr: no
Slight chalking; no crackingor peeling: no breaking away of coarse particles; good resistance t o abrasion 75 68 : 32 “ X X ” zinc oxide 21 % 83.4 248 299 10.9 12.5 Considerable chalking: no B. C. W. L 49% cracking, peeling or Talc 30 % hreaking a w a y of coarse particles b u t only medium resistance t o abrasion. T h e paint showed a yellow discoloration In using t h e cryptometer i t was necessary t o screen o u t the very coarse material. This causes slight inaccuracies but does not appreciably affect the relative value of t h e results.
I S D C S T R I A L A S D EXGIIVEERI~YGCHEMISTRY
970
T a b l e V-Composition,
T’ol. 18, s o . 9
H i d i n g Power, Visibility, and E n d u r a n c e of T y p i c a l Traffic Paints (Concluded)
POWSR~Computed at 80% Bright- Relative brightness Sq. ft./ Sq. ft./ VISIBILITY ness gal. Per cent gal. Night Day 79.0 260 12.5 248 9.0 .-HIDING
Paint 76
Pigmentvehicle ratio --Pigment--71:29 “ X X ” zinc oxide B. S.L. Talc
Size of inert particles Microns 21% 49% 30 %
Vehicle
Corn. A 57:43b
Lead chromate Lead sulfate Inerts
3770 9% 54 %
All finer than Unknown; contains 150 65Y0 volatile. Slow drying required 5 hours to dry tack-free
54.5
401
178
1.2
9.2
Corn. B 67:33b
Zinc oxide B. S. L. Inerts
37%
All finer than Unknown; contains 150 60% volatile
73.8
256
195
2.0
11.0
Lithopone Inerts
60%
hpprox. 5057, Unknown: contains larger than 75% volatile 150
85.2
192
Com. C 68:32b
18%
45% 40%
260
11.0
12.6
Effect of Combined Accelerated Weathering and -4brasion Test Considerable chalking; n o cracking, peeling, o r breaking away of coarse particles; fair resistance to abrasion. The paint showed a brown discoloration Very heavy chalking; no cracking or peeling; very poor resistance to abrasion; uneven discoloration to orange and red-brown Very heavy chalking: no cracking 01 peeling; very poor resistance to abrasion C:onsiderable chalking. no cracking or peeling.’ some breaking away ok coarse particles; film, appears porous: poor resistance to abrasion
b Probable composition (by analysis).
Extinction of Methane-Air Flames b y Some Chlorinated Hydrocarbons’” By H. F. Coward3 and G . W. Jones4 PITTSBLRGH EXPERIMENT S T A T I O NBUREAU , O F MINES, PITTSBURGH, PA
The nature of the extinctive action of inert gasesH E extinctive effect of sufficed to raise the Iower carbon dioxide, nitrogen, argon, helium-on flame has i n e r t gases on methlimit of methane nearly 2 per been e!ucidated by the determination of the limits of a n e - a i r f l a m e s has cent, whereas we should not inflammability of methane in atmospheres composed r e c e n t l y b e e n studied by expect, on the thermal conof air mixed with increasing amounts of inert gas. ineans of determinations of siderations just mentioned, A new series of results, now presented, shows the inthe limits of inflammability that the lower limit would b e fluence of the vapors of certain chlorinated hydrocaraffected to the extent of more (lower and higher) of methane bons on the inflammability limits of methane in air. in atmospheres composed of than a fraction of one-tenth A comparison of the fire-extinguishing properties of of 1 per cent. ordinary air mixed with incarbon tetrachloride and carbon dioxide is included. If Jorissen’s experiments creasing amounts of carbon are right, he has discovered dioxide, nitrogen, argon, a i d helium. The limb of inflammability approached nearer some extraordinarily powerful fire-extinguishing agents. The and nearer as inert gas was added in increasing proportions writers have therefore made a thorough reexamination of the t o the atmosphere, until finally they coincided. The experi- influence of certain chlorine deriyatives of methane, ethane, mental results shown in Figure 1 led t,o the conclusion that and ethylene, on the limits of inflammability of methane. the relative extinctive effects of carbon dioxide, nitrogen, For this purpoie they have not followed Jorissen’s experiand argon are explained by their relative heat capacities, mental procedure, and it is therefore neceqsary to state in the gas of greater heat capacity having the greater extinctive some detail their criticisms of his work. He used three action. The abnormal behavior of helium, which has a similar vnall (3bcc.) burets with sonievhat different spark thermal capacity equal t o that of argon, was ascribed to its gaps at the top, so that downward propagation of flame was observed in each case. For inethane the lower limits for the exceptionally high thermal conductivity. In the light of these conclusions, some recent results of three burets were 5.4, 3.7, and 4.9 per cent methane, reJorissen6 and his co-workers are exceptional. They found, spectiT-ely. This inconsistency proves that Jorissen was not for example, that the presence of less than 1 per cent of the observing whether or not his mixtures were capable of propavapor of tetrachloroethylene or tetrachloroethane in air gating flame per se. His apparatus is not satisfactory to insure certain ignition and also to give the resultant flame Presented before the Section of Gas and Fuel Chemistry a t the 7 l s t a long enough “run” to enable observers to judge whether i t Meeting of the American Chemical Society, Tulsa, Okla., .4pril 5 to 9, 1926. 2 Published with approval of the Director, U. S. Bureau of Mines. is self-propagating when it has lost the initial impulse due The work reported in this communication forms part of the program of to the source of ignition. cooperative work between the Bureau of Mines (U. S. .Iand .)the Safety Jorissen’s failure to appreciate the experimental requisites in Mines Research Board (Great Britain), and was undertaken during the in this type of work is further illustrated by the following visit of one of the writers t o the Pittsburgh Experiment Station of the Bureau. quotation from his first paper:
T
1
Principal assistant, Safety in Mines Research Board, Great Britain. Associate chemical technologist, U. S . Bureau of Mines, Experiment Station, Pittsburgh, Pa. 5 Coward and Hartwell, J . Chem. S O L . ( L o n d o n ) , 129, 1522 (1926). 8 Rec. t m v . chim., 43, 80, 591 (1924); 44, 132 (1925). a
4
From Bunsen’s observations on the explosibility of hydrogen oxygen mixtures a lower explosion limit of about 6 1 vol. per cent may be calculated. When we compare this limit with t h a t for hydrogen air mixtures as determined by J. Roszkowski, viz.:
