908
T H E J O C R A T A L O F I - V D C S T R I A L A4LVDE-VGISEERI-VG C H E M I S T R Y
INVESTIGATIONS WITH THE U. S. BUREAU OF MINES MODIFICATION OF THE ABEL-PENSKY AND PENSKY-MARTENS FLASH-POINT TESTERS By I R V I N G
c. &.LEN
AND
A.
s.CROSSFIELD
I n t h e handling of l a m p oils, particularly in mines and in buildings where open lights are used, i t is important t h a t a relatively safe oil. i. e . . one with a high flash point. be employed. Equally important is t h e determination of t h e inflammability of all oils in common use. This paper, which is a brief of Technical Paper No. 49. published b y t h e Bureau of 1Iines in t h e interest of greater safety a t mining a n d metallurgical plants. does not aim t o establish definite flash points for oils b u t describes t h e instruments a n d methods of testing t h a t can be used a s a basis on which t o establish such flash points. THE FLASH P O I S T
I n t h e various methods used for determining t h e flash point of a n oil t h e temperature a t which its vapor flashes is not a definite factor b u t is dependent on a number of physical and chemical conditions not under t h e control of t h e operator. I t is not a n indication of t h e value of a n oil for a n y particular purpose. I t is a n indication only of t h e temperature a t which t h e oil gives off vapors in such proportions t h a t they form a n inflammable mixture with t h e air. If exposed t o an electric light or a flame t h e mixture will ignite and t h e flame extend throughout t h e mixture, t h a t is. a n explosive mixture of vapor and air is formed. T H E F I R E HAZARD
The flash point, although probably t h e most important factor, will n o t , b y itself, determine the fire hazard of a n y substance. T h e Ere hazard of a substance is also affected b y t h e volatility. t h e boiling point. t h e vapor pressure, t h e vapor density, t h e diffusibility and tendency of t h e vapors t o travel and their explosive limits in air, its tendency t o chemical change, t h e quantity of heat liberated per unit of time a n d unit of volume, t h e temperature of t h e flame, t h e corrosive action and toxic properties of the substance a n d of its products of combustion, its behavior toward water both before a n d after ignition. and t h e tendency of t h e substance t o leak. % . requirement t h a t a n oil has t h e highest practicable flash point, tending thereby t o reduce t h e fire hazard t o a minimum, is praiseworthy and humane. T o require too high a flash point m a y impair the burning qualities of a lamp oil a n d also work a hardship on the r e h e r . However, t h e immediate profits of t h e refiner should be deemed less important t h a n t h e safety of t h e user and t h e protection of the public against possible loss of life and of property by fire, T h e fire hazard of lubricating oils is of importance Tyhen t h e lubricants are used in rapidly running machinery, as in spinning mills. wood mills, e t c . , or in factories containing combustibles and in compressors for air, ammonia, or other gases. Particular attention should always be given t o the Paper presented a t t h e 48th meetin4 of t h e A . C. S.,Rochester, September 8-14. 1913, by permission of t h e Director of the U. S. Buresu of Mines.
T'ol. 5, S o .
11
handling, storage, and inspection of all inflammable liquids. The Bureau of Mines in Technical Paper No. 49 has recommended t h e adoption of a modified form of the -1bel-Pensky a n d Pensky-Martens testers for t h e determinations of the flash points of oils flashing below 1jo0 C. T h e reasons for t h e recommendations of these testers are clearly set forth in Technical Paper No. 49. a brief abstract of which includes ( I ) t h e reasons for the necessity of exact determination of flash points of oils t o determine t h e fire hazard with their use; ( 2 ) t h e historical development of flash-point testing with descriptions of testers in use; (3) t h e different factors t h a t influence t h e obtaining of exact a n d concordant results; (4) a n d directions for the use of t h e two testers recommended. The modifications of t h e older forms of Xbel-Pensky a n d Pensky-3lartens testers consist of t h e following: each cup has been fitted with a n annular overflow cup into which t h e excess of oil due t o t h e expansion on heating flows through a small opening in t h e side of t h e cup on a level with t h e filling point. This assures t h e volume of t h e oil and t h e volume of t h e vapor mixture above t h e oil remaining constant. The XbelPensky tester is provided with a paddle-wheel stirrer identical with t h a t of t h e Pensky-IUartens, while t h e automatic slide of t h e Abel-Pensky tester has been fitted t o the Pensky-Martens cup. However. in t h e last change i t was found necessary t o raise t h e clock work on posts above t h e hot b a t h a s t h e intense heat drew t h e temper from t h e spring. T h e two testers as recommended are identical with t h e exception of t h e use of t h e water b a t h for t h e testing of low flash oils a n d t h e metal-air b a t h for those of high flash point. T h e cups, t h e automatic opening devices and t h e stirrers of t h e two testers are interchangeable. A n investigation undertaken in these laboratories indicates t h a t t h e Pensky-Martens tester can be used very satisfactorily for t h e testing of low flash-point oils though t h e temperature regulation is not as nice as with t h e water-jacketed Abel-Pensky tester. T h e same conclusion has been reached b y other investigations.' Each tester is fitted with gas or oil igniti'on burners. T h e present paper includes results of a brief investigation with t h e t w o testers. A degree of accuracy greater t h a n 0 .j o C. for oils flashing below 100' C. and I o o C. for oils flashing above 100' C. was not a t tempted a n d a n y fractions of degrees reported in subsequent tables are derived as averages of several tests or from thermometer, barometer or instrument corrections. S T A K D A R D I ZA T I 0 N
0 F I K S T R C ME S T S
To obtain comparable results t h e t w o instruments were compared with a n Abel-Pensky tester standardized in 1908 b y t h e Physikalische Technische Reichsanstalt, certificate No. S. & R. 31 14. Determinations of flash points of three different oils were made on the three instruments. Results .obtained are t h e averages of five tests agreeing within 0 .j" C. a n d a r e shown in Table I . 1 Dr H W e b e , "Die Obere Brauchbarkeitsgrenze des Abel-Penskyschen Apparates s n < l seine l'ergleichung m i t dem Penskyschen Flammpunktpriifer, Petvoleurn. 1913, Band V I I I , S. 1061.
SOY-.,
T H E JOI'R.\.'AL
I913
TABLE I-COMPARISOK OF BURElU
OF M I X E S
O F I S D 1 7 S T R I = l L A A Y D E.VGISEERILJ7G C H E M I S T R Y TESTERS WITH .%BEL-PESSKY
TESTERS . 8. R . 3114 Average of five tests each
F. P. b y F. P. hl- B. of 31.
Sample
X
NO.1086 . . . . No. 1 0 8 i . . . Average
..
AhrlPensky S . 8- R . 3114
Pensky
47 3' 36 3'
48 0' 37.0'
.%bel-
44 ,To ,
Difference
B. of hl. modification Penskyhlartens
+ O 7' +O.io +1.O0
49.00 37.8' 46.2'
modification
45.5O
_,
F. P. by
__
~
..
,
Difference 1.1.70 T I 5' -1.;'
__
~
0 80
1 6'
In all results hereafter reported t h e abol-e corrections have been made. T h e large corrections obtained make i t advisable t o ha\-e all instruments intended for exact work compared with some fixed standard. TSE OF GAS A S D
OIL I G X I T I O S FLAXIES
T h e use of gas or oil t e s t flames is optional. Comparative tests made. using natural gas. colza oil and lard oil a s ignition flames, gave results with a maxim u m difference of 0 . 3 ' , which is well within t h e error of manipulation. -1 petroleum distillate. ' . 3 0 0 ° burning oil." on t h e other h a n d . gave a flash approximately 0 . 8 ' t o o high a n d t h e use of such a n oil as an ignition flame is n o t recommended. T h e difference is probably accounted for b y t h e fact t h a t t h e latter flame was quite difficult t o regulate, d u e t o its rapid flow through t h e wick and t h a t t h e combustion was incomplete as indicated b y a bright luminous flame, which in itself m a y have obscured t h e first flash. F o r ease of manipulation a gas flame is most desirable.
909
recorded t h a n is actually t h e case. This is clearly shown in Table 111. F u r t h e r . t h e greater t h e r a t e of heating t h e greater will b e t h e convection currents a n d consequently t h e greater will b e t h e difference between t h e t e m p e r a t u r e of t h e oil a t t h e circumference a n d t h e t e m p e r a t u r e a t t h e center of t h e cup. Also t h e higher t h e flash point t h e greater will be t h e t e m perature differences. T h e differences are almost entirely remoi-ed b y t h e use of a stirrer a n d it has been found easier also t o get concordant results in a stirred c u p t h a n in one t h a t is without a stirrer. Different investigators ( B . of AI. Tech. Paper KO. 49,p. 1 2 ) have found t h a t a definite filling of t h e c u p has a very appreciable influence on t h e determination of t h e flash point. Filling t h e cup above t h e point raises t h e flash point. T h e reasons for this are quite a p p a r e n t . T h e oil as i t is heated expands. t h e surface of t h e oil is brought nearer t h e test flame a n d a lower flash point results. Expansion of t h e oil reduces t h e volume of t h e gas mixture. a n explosive mixture is formed a t a lower temperature a n d consequently a lower flash point is recorded. 9 n explosive mixture would be obtained a t a lower temperature from a fixed weight of oil t h a n from a fixed volume a n d a lower flash point would result. T o do an-ay with these sources of error t h e modified testers have been fitted with overflow cups so t h a t a s t h e oil is heated t h e increase in volume is r u n off a n d both volume of oil a n d volume of T-apor mixture are k e p t constant. T h e aboi-e assumptions are borne out in Table I V . TABLE~\'-COZIPARISOXO F
FLASH P O I K T WITH C O S S T A N T
COSSTAXT
\vEIGHT
ISD
VOLUME
Average of three tests
TABLE 11-COMPARISOS
Sample 1087 . . , , , , . . . . . . . . Kerosine X... . , . . .
OF
FLASH POIXTS
WITH G A S A N D OIL
Gas test flame
Lard oil test flame
Colza oil flame
45.5 48.0
45.4 48.1
45.2 47 7
ISFLUEI-CE
TESTF L . 4 M E S
Sample I n s t r u m e n t used
B. oi >I. modification of Abel-Penskv
O F STIRRER
T h e h e a t is applied t o t h e oil from t h e bortom a n d sides of t h e cup with t h e result t h a t there are convection currents set u p within t h e oil Ivith t h e general direction across t h e b o t t o m of t h e c u p , u p t h e sides. across t h e t o p a n d down t h e center a n d past t h e thermometer bulb. Consequently, t h e oil as i t passes t h e TABLEIII-?XFLUENCE
OF
STIRRER
.%verajie of three tests each
Kerosine X . , . , . , 1086. . . . . . , , . . . . . . . 46.2 1087.. . . . . . , , . . , . 1092 . . . . , . . . . . . . . 1 1 7 . 0 1095 . , . . . . , . , . . . . 184.i 1096 . . . . , . . . . . 196 4
... . . 45.4 115 1 183.0 195.6
..
..
3i.0 45.5 ,.
37.1
45.2
..
, ,
.,
..
46.2 35.6 44.3
45.7 35.1 45.8
... ... ..
..
t h e r m o m e t e r is slightly cooler t h a n t h a t a t t h e circumference of t h e surface a n d a lorn-er flash point mill be
1087 1092 1095 1096
F . P. B. of hl. F . F. B. of hl. modified modi6cd Pensky-Martens Pensky-3Iartens constant 7.01. constant weight 46.2
45.8
117.0 184.7
115 1 183.0 195.3
196.4
.
Difference
0.4 1.9 1.7 1.3
The suggestion has been made t h a t t h e 01-erflow oil in t h e outer cup will he much hotter t h a n t h e temperature indicated b y t h e thermometer ivithin t h e cup, t h a t t h e 2-apors liberated will pass b a r k into t h e cup a n d give a flash belon- t h e t r u e flash of t h e oil, b u t i t is beliei7ed t h a t such conditions d o n o t exist. In t h e first place t h e cup is so constructed t h a t t h e b o t t o m is directly exposed t o t h e h o t b a t h a n d if stirred t h e oil in t h e cup is a t a temperature not appreciably lower t h a n t h a t in t h e overflow cup. T h e volume of t h e oil t h a t overflows is snlall compared with t h a t in t h e c u p ; a n d t h e q u a n t i t y of vapors liberated from such a small volume even a t a slightly higher temperature would have little effect on t h e flash point. particularly t h a t fraction of t h e small 1-olume which might pass hack into t h e cup. Also, i t is hardly t o be assumed t h a t t h e 7-apors would pass back i n t o t h e cup rather t h a n escape around t h e loose fitting ring of t h e overflow cup. T h e views above are borne o u t b y t h e fact t h a t in no case was t h e f a s h point of a n oil determined in t h e cup with t h e overflow lower t h a n t h a t obtained when t h e overflow out-
T H E JOUR,VAL O F 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
910
let was plugged. As further proof, comparisons were made of t h e flash point of a n oil obtained in t h e usual way a n d of t h e flash obtained b y placing a q u a n t i t y of low flash oil in t h e overflow cup. T h e results are shown in Table \-. TABLE V
Sample
Nc . Test
1087
No. 1 . . . . . . . . . . . . . .
No. 3 . . . . _ . . . .
.
.,.
Average.. . . . . . . . . . . .
Sample No. 108i with S cc. of No. l08G (F. P. = 3 7 ’ ) in the overflow cup
45.4
45.4 45.4
45.8
45.4
-
-_
45.5
45.4
I n s t r u m e n t used
B. of hZ. modified Abel-Fensky
S U 11 31 A R Y
T h e i m p o r t a n t factors t o be considered in t h e construction a n d manipulation of a n i n s t r u m e n t t o determine t h e flash point of a n oil m a y be stated as follows : ( I ) T h e conditions under which t h e test vapors are generated should be as like as possible t o t h e conditions found in practice. ( 2 ) Corrections should be made for variations from t h e normal barometric pressure. (3) T h e size a n d dimensions of t h e cup. (4) T h e size, shape, d e p t h of immersion a n d exposed p a r t of t h e thermometer should be definite a n d in every case t h e thermometer should be calibrated. (j) T h e oil should never be exposed for a n y length of t i m e a t temperatures greatly higher or lower t h a n the normal temperature. (6) T h e r a t e of heating on testing should be constant a n d a t a r a t e of a b o u t I O C . for l a m p oils a n d 3 O - j O C. for high flash-point oils. ( 7 ) T h e oil should be uniformly stirred during t h e test. (8) T h e test flame should be of definite size, should be exposed a t a fixed distance above. t h e surface of t h e oil a n d exposed for a definite length of time. (9) A11 water should be removed from t h e oil prior t o testing. ( I O ) I n general testing, so far as possible, t h e effect of t h e personality of t h e operators should be eliminated a n d t h e manipulation of t h e tester made entirely mechanical a n d automatic. T h e most accurate tester a n d t h e tester t h a t most nearly reproduces actual working conditions should be adopted for official tests. Considering all of t h e above factors, it is believed t h a t these t w o testers, t h e Abel-Pensky a n d t h e P e n s k y - M a r t e n s , as modified b y t h e Bureau of htines, most nearly meet with t h e desired conditions. T h e Bureau of Mines flash testers have been officially adopted b y t h e Kational Fire Protection Association, t h e Independent Petroleum h,Iarketers’ Association of t h e United States a n d a r e now being considered for adoption b y committees on tests of t h e National Petroleum Association, t h e American Chemical Society, t h e American Society for Testing Materials a n d t h e International Petroleum Commission. B U R E A UOF M I N E S PITTSBURGH
Vol.
s 9 No.
11
THE TITRATION OF CALCIUM AND MAGNESIUM IN THE SAME SOLUTION By PAULJ. Fox’ Received September 9, 1913
Few determinations are more frequently made in chemical laboratories t h a n those of calcium a n d magnesium, a n d t h e writer was led into the following investigation with a view t o lessening the labor required for these determinations: T h e titration of calcium as oxalate with permanganate is, of course, a well known a n d s t a n d a r d process, a n d . t h e titration of magnesium as magnesium a m m o n i u m arsenate with sodium thiosulfate in acid solution after t h e addition of potassium iodide has been described b y Meade* a n d b y G. B. Frankforter a n d Lillian Cohen.3 It has occurred t o t h e writer t h a t it might be possible t o combine these processes in one operation b y first precipitating t h e calcium as oxalate, a n d t h e n in t h e same solution a n d without filtering, precipitating t h e magnesium as magnesium ammonium arsenate, filtering off a n d washing t h e combined calcium oxalate a n d ammonium magnesium arsenate, dissolving in acid, titrating t h e calcium oxalate with potassium permangante a n d t h e n t h e magnesium ammonium arsenate with sodium thiosulfate after t h e addition of potassium iodide. As will be shown in t h e sequel, this combined method is perfectly feasible, t h e t w o titrations not interfering with each other. T h e titration of calcium as oxalate calls for no rem a r k except t o observe t h a t t h e objection t h a t t h e calcium sulfate formed prevents complete decomposition of t h e calcium oxalate is not, in t h e writer’s experience, valid. With moderate skill in manipulation, i t is always possible t o obtain good results. I n t h e titration of t h e arsenate, however, certain irregularities were encountered. For example, following approximately t h e directions in t h e paper of F r a n k forter a n d Lillian Cohen, when I O cc. portions of a certain solution of a m m o n i u m arsenate were acidified, a n d made u p t o IOO cc. so t h a t I O O cc. contained a b o u t ~j cc. concentrated sulfuric acid, cooled, j grams potassium iodide added, a n d titrated after standing j minutes, 2 1 . 2 1 , 21.j2, a n d 2 0 . 7 8 cc. thiosulfate solution were required t o decolorize t h e solution. All t h e portions were, of course, measured out b y t h e same pipette a n d measured over t h e same portion of the burette. T h e figures given are selected from m a n y a n d are representative of t h e magnitude of t h e variations. T h e y were measured out a n d titrated a t different times, a series t i t r a t e d a t t h e same time showing less variation. T h e e n d point was always certain a n d definite. M a n y experiments were made t o find t h e cause a n d remedy for t h e irregularities, b u t t o cite t h e figures in detail would scarcely be profitable. T h e a d v a n tages of t h e improvements suggested are more or less self evident. T h e principal causes of irregularity -assuming of course t h a t t h e iodide used is free from iodate or other substance capable of setting free iodine 1 Scientist in Soil Investigations, Bureau of Soils, U. S. D e p t . of Agriculture. 2 R . K. Meade, Jour. A m . C k e m . SOL.,21, 146 (1899). 3 Jour. A m . Chem. Soc., 29, 1464 (1907).
