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
J u l y 1 1916
of t h e Kjeldahl method for determining nitrogen are looking for a cheaper substitute t o t a k e t h e place of t h e more expensive potassium sulfate. Quotations recently received a t this laboratory from several firms range in price from $ 1 . 2 5 t o $ 2 . 2 5 per lb. for t h e powdered chemical suitable for use i n nitrogen work, while quotations on suitable sodium sulfate were only I j c. per lb. Because of t h e similarity in chemical characteristics between potassium sulfate a n d sodium sulfate, a series of determinations was made t o compare t h e use of these two salts in making nitrogen determinations. I n t h e first trials, where I O g. of t h e water-free salts were used in comparison, both worked very nicely during digestion, b u t on cooling, t h e digest in which sodium sulfate was used caked into a solid mass, a n d a s this was objectionable 7 t o 8 g. of sodium sulfate were used with t h e results shown in Table I. As nitrogen determinations m u s t be made on rnaterials differing widely in nitrogen content, i t was t h o u g h t well t o use such a variety as one might ordinarily be called upon t o analyze in every-day work. For this reason t h e t e n different samples listed in t h e t a b l e were used i n these determinations. TABLE I (RESULTSIN PERCENTAGES) THE GUNNINGCOPPER METHOD THE OFFICIAL SUBSTITUTING GUNNINGCOPPERMETHOD No. of SODIUM SULFATE No. of SUBSTANCES Dets. Max. Min. Av. Dets. Max. Min. Av. Dried b l o o d . , . 3 14.97 14.93 14.95 3 14.96 14.92 14.95 12.67 12.69 Casein . . . . , , , , 3 12.72 12.68 12.70 3 12.71 8.89 8.99 3 9.00 8.96 8.98 Milk albumin.. 6 9 . 0 7 3.46 3.49 3 3.51 3.49 3.50 Fertilizer.. , , , 3 3.51 3.61 3.73 3.77 Alfalfa leaves ... 5 3 . 7 8 3.71 3 3.80 Alfalfa s t e m s . , 3 1.63 1.55 1.59 3 1.63 1.59 1.62 1.32 1.35 1.37 Cob chop , 3 .1.36 1.35 3 1.38 0.90 0.93 Bone meal 3 0.96 0.92 0.94 3 0.94 0.50 Skim milk 3 0.53 0.52 3 0.53 0.51 0.52 0.038 0.041 Soil.. ...... 4 0.043 3 0.041 0.037 0.039
.
..... ..... ..... I
.
.
T h e figures in the table explain themselves, a n d as these t e n samples include compounds of t h e highest t o t h e lowest nitrogen content, t h e writer feels confident in saying t h a t he believes sodium sulfate can be used instead of potassium sulfate when determining nitrogen in a n y kind of material. T h e analyses were carried out under exactly duplicate conditions. T h e period of digestion was 2 hrs. after t h e solution cleared. Sodium sulfate. when used in t h e amounts mentioned, did not i n a n y way prove objectionable in this work. It proved itself just as good a n oxidizing agent as potassium sulfate a n d as i t has a higher boiling point, i t would be expected t o be even better t h a n potassium sulfate. T h e writer does not maintain t h a t sodium sulfate is preferable t o potassium sulfate in nitrogen determinations. There are cases where caking will t a k e place, although this can readily be avoided b y diluting as soon as cool. As far as chemical efficiency is concerned, t h e t w o chemicals compare very favorably. Where a large number of nitrogen determinations are being made a n d potassium sulfate is ordered in 5 0 a n d IOO lb. lots, a great saving will be realized b y using sodium sulfate; as much as $60 c a n be saved on one order of 50 lbs. I t should be mentioned here t h a t we have found it more convenient a n d inexpensive t o use copper wire instead of copper sulfate. As is known,' t h e use of 1
Journal A . 0. A . C., 1, No. 4, P a r t 11. 18-21-23.
587
copper sulfate has been adopted officially for use in nitrogen determinations. I t s good points have previously been discussed' and need no further elaboration. Pieces of copper wire approximating 0 . I g. can readily be cut with a wire cutter. KANSASSTATE AGRICULTURAL COLLEGE MANHATTAN
SOME DATA ON THE OXIDATION OF AUTOMOBILE CYLlNDER OILS By C. E. WATERS= Received April 1, 1916 INTRODUCTION
I t has long been known t h a t mineral oils become oxidized when subjected t o t h e combined action of sunlight a n d air. T h e literature of t h e subject was r a t h e r fully reviewed in a paper published some time ago.3 T h e so-called "carbonization" of automobile cylinder oils is due, t o only a very limited extent if a t all, t o cracking, b u t is caused b y oxidation4 a n d subsequent polymerization. I n order t o learn whether there is a n y close connection between t h e r a t e of oxidation of different oils on exposure t o light a n d air, a n d their carbonization values at elevated t e m peratures, both before a n d after oxidation in t h e light, a n extended series of tests was made with three automobile cylinder oils of well known brands. Certain other constants were also determined. As supplemental t o t h e above, t h e influence of t h e time a n d temperature of heating upon t h e carbonization value was also studied. A sufficient supply of each of t h e oils was purchased in t h e open market. I n order t o remove adventitious particles of iron rust or other material t h a t might affect t h e carbonization values a n d possibly other determinations,j t h e samples were filtered directly into clean cans. One-liter portions were kept for convenience in d a r k brown bottles. The flash a n d fire points were as follows, t h e determinations being made in t h e Pensky-Martens closed cup apparatus: Oil No. 1 Flash point ............._..215' Fire point , . . . . , . . . . . , , , . . 270'
.
2
210' 2-50"
3 205; 250
OXIDATION I N S U N L I G H T
In the earlier paper on this subject6 i t was shown t h a t when a n oil is oxidized i n t h e sunlight some water a n d carbon dioxide are given off. T h e oil becomes highly acid a n d a n insoluble oxidation product is thrown down, sometimes after only a few hours' insolation. In order t o follow t h e changes in weight of t h e oils under investigation, seven Io-g. portions of each were placed in 150-cc. Erlenmeyer flasks, t h e mouths of which were covered with filter paper 1 A. J. Patten, Journal A . 0. A . C., 1, No. 3, pp. 394-395; 0 F. Jensen, THISJOURNAL,7 (1915), 38-39. 2 Published by permission of the Director of the Bureau of Standards. T h e complete paper has just appeared as Technologic Papev 73 of the Bureau of Standards. a Bureau of Standards, Bull. 7 (1910), 227-234; THIS JOURNAL,2 (1910), 451-4. 4 Bureau o f Standards, Bull. 7 (19101, 372, 375; Bureau of Standards, Technologic Paper 4 (1911), 11; THIS JOURNAL, 3 (1911). 236, 237, 815. Bureauof Standards, TechnologicPaper 4 (1911), 10.13; THISJOURNAL, 8 (1911). 815. 6 Bureau of Standards, Bull. 7 (1910), 232; THISJOURNAL, 2 (1910), 453.
588
T H E JOURNAL OF I N D U S T R I A L A J D ENGINEERING CHEMISTRY
to exclude dust. The flasks were held in racks, the bases of which were covered with white paper. On every bright day, for a total of 438 hrs., they were placed outside a window facing south. Bt first t h e flasks were weighed every day, b u t later on, as t h e rate of oxidation became less rapid, this was done only every 3 or 4 days. All weighings were made against a tare. Twenty-one flasks Jvas all t h a t could be placed, without shading one another, upon the window-sill. Great care was taken t o keep the racks level, and t o avoid getting t h e oil on t h e sides of the flasks, thus increasing t h e area of oil surface exposed. Only three
Expo-
T A B L E I-DATA O N OILS GAIN Ig ~ ‘ E I c H T
sure Hrs.
W o . 1 No. 2 S o . 3
51.5 90
9 . 1 19.3 18.2 62.6 79.7 75.5 8 8 . 0 107.7 104.0
Milligrams
;2y,5 iz::;
;:j
205 249 289 327 364
188.2 197.0 212.6 227.2 237.4 246.7 252.1
::$
1 7 2 . 6 188.8 180.7 197.4 195.4 212.7 210.5 227.2 220.4 237.8 229.9 247.4 236.2 252.9
Expossn
’IO SCKLIGHT AND A I R
ExpoAcinxTY sure Milligrams KOH Hrs. No. 1 No. 2 No. 3 Pione 0.06 0.04 0 . 0 3 22 0 . 0 8 0 . 0 8 0.08 40
rjj
lei.> 118
149 I74 208.5 238 289 333 419
T‘ol. 8, NO. 7 CARBONIZATION
0.09 0.10 0.09
z:;; ;:;
;:
Percentages I No. 1 No. 2 No. 3 0.14 0.17 0.30 0 . 2 3 0 . 2 6 0.38 0 . 3 0 0.33 0 . 5 2
0.17 0.38 0.50 0.86 1.22 1.44 2.32 2.40 3.40
0.25 0.50 0.67 1.08 1.43 1.6’ 2.68 2.94 3.67
0.28 0.30 0.38 0.40 0.45 0.42 0.52 0.66 0.90
0.25 0.51 0.71 1.03 1.36 1.65 2.74 2.91 3.70
;:; ;:;;0:; 0.37 0.35 0.44 0.48 0.59 O.63 0.74 0.92 1.38
0.54 0.53 0.64 0.73 0.82 0.8’ 1.11 1.25 1.75
T h e curves shown in Fig. I are plotted from t h e average gains for each set of flasks and the number 2.
flasks of each set were exposed for the entire 438
hrs., because on two occasions two flasks of each oil were used for special tests. Although t h e remaining flasks were those showing gains furthest from the respective averages, yet a t t h e end of t h e experiment the differences between t h e highest and the lowest gain for each oil were only 7 . 5. 4 . 5 and 6 9 mg., respectively. These are the maximum differences found during the test. I n Table I are given the average gains in weight for t h e three oils a t approximately equal intervals.
of hours they were exposed t o light. I t will be seen t h a t . except for breaks caused b y unfavorable weather, t h e curves apparently show t h a t the oxidation proceeds a t a slowly decreasing rate. B u t it must be remembered t h a t t h e gain is t h e algebraic s u m of t h e oxygen absorbed and the carbon dioxide and mater 10st.l Hence cur\-es showing t h e actual r a t e of oxidation would lie somewhat above those drawn. T o follow the changes in weight, carbonization, and acidity, not t o mention a fern special tests, more 1
Loc
CZt
J u l y , 1916
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
t h a n 200 ten-gram portions of oil were used. T have h a d these in separate flasks would have been impracticable, so t h a t about a liter a n d a half of each oil was oxidized in crystallizing dishes 2 4 cm. in diameter. T h e dishes were covered with mTatch glasses which excluded dust b u t did not prevent access of air. At certain intervals, enough t o make t h e desired tests was removed, after thoroughly stirring t h e contents of t h e dishes. Satisfactory sampling was not difficult even after t h e insoluble oxidation product1 began t o form, because t h e particles settled very slowly through t h e oil. It was foreseen t h a t t h e oil in t h e dishes could not be oxidized as rapidly as t h a t in t h e flasks, on account of its being in a much deeper layer, For this reason t h e curves showing t h e increase in acidity a n d carbonization are not strictly comparable with those showing t h e gain in weight. This does not, however, affect t h e general results. The more important determinations were made on samples t h a t h a d received t h e same treatment. I K C R E A S E I N ACIDITY BY OXIDATION
From time t o time representative samples were removed from t h e dishes. Ten-gram portions were warmed with measured volumes of alcohol a n d gasoline and titrated with 0 . I N alkali, using phenolphthalein as indicator. At first there was no difficulty about this, b u t as t h e oils became more strongly acid t h e end-point was increasingly difficult t o detect, owing t o their great tendency t o emulsify. This is not surprising when it is remembered t h a t soap is formed b y t h e action with t h e a l k a l i 2 The results appear in Table I a n d are also plotted in Fig. I. T h e ordinates show t h e number of milligrams of potassiuA hydroxide required t o neutralize I g. of oil. I t will be seen t h a t t h e curves for Oils 2 a n d 3 lie very close t o one another throughout t h e greater part of their extent, t h e maximum deviation being equivalent t o only 0 . 0 7 mg. of caustic potash. In this respect t h e y resemble t h e curves showing the increase in weight. I n both cases also, Oil I lies below these two. The general t r e n d of t h e curves indicates t h a t t h e rate of formation of acids gradually increases. A maximum acidity must eventually be reached, b u t t h e curves give merely a n uncertain indication of this b y their slightly decreased slope. The two abrupt breaks in t h e curves between 69 a n d 149 hrs. are t h e results of unfavorable weather. It was found t h a t t h e percentage of t h e insoluble oxidation product thrown down b y petroleum ether is not proportional t o t h e gain in acidity. T h e percentages f o u n d a t t h e end of t h e exposure test were 0 . 3 8 , 0 . 5 I a n d 0 . 6 0 , respectively. THE C A R B O K I Z A T I O K O F O I L S O X I D I Z E D 1.U S U S L I G H T
The carbonization values of t h e oxidized oils were determined on samples taken a t t h e same times as those used for t h e determination of acidity. T h e procedure followed was t h e same as described in earlier Bureau of Standards, Bull. 7 (1910). 230; THIS JOURNAL, 2 (1910). 452. Schaal, D R. Pat. 32,705; Chem -Ztg., 9 (1885). 1520.
* Cf
589
papers,’ b u t a n electrically heated a n d controlled air b a t h was used instead of one heated b y gas. Tengram portions of oil, contained in Ijo-cc. Erlenmeyer flasks, were heated t o 2 j o o for 3 hrs., allowed t o cool a n d diluted with j o cc. of petroleum ether. The flasks were t h e n tightly corked a n d set aside for about 24 hrs. The precipitate was filtered off in a Gooch crucible prepared with a disk of filter paper (S. & S. No. 589 blue ribbon) covered with a thin layer of asbestos t o keep it in place. It was washed with petroleum ether, dried a t 9 j-10oo, a n d weighed. T h e results obtained are included in Table I and are shown in Fig. I . The curves showing t h e percentages of carbonization oE t h e oxidized oils are strikingly different from those showing t h e gains in weight and in acidity. Oils 2 a n d 3 no longer give nearly t h e same values, b u t quite different ones. After 419 hours’ exposure t o sunlight, Oil 2 has a carbonization value t h a t is slightly greater t h a n t h e mean of t h e values for t h e other two oils. A similar relationship held for t h e amounts of insoluble oxidation product formed, a t ordinary temperatures, in sunlight. MISCELLANEOUS DETERMINATIONS
I n order t o learn whether or not there is any connection between t h e tendency of a n oil t o oxidize a n d certain other of its properties, t h e power t o form emulsions with water a n d t h e MaumenC a n d iodine numbers were determined. DEMULSIBILITY-when oils are vigorously stirred or shaken with water, more or less permanent emulsions are produced. T h e rates a t which t h e two liquids separate differ widely, some emulsions lasting for days, while with others t h e two original layers reappear i n a few minutes. The “demulsibility,”2 or r a t e of separation of a n emulsion into layers, is a n indication of t h e quality of a n oil. A high demulsibility, measured in cubic centimeters per hour, for instance, indicates a n oil of good quality. W. H. Herschel, of this Bureau, using a n apparatus devised b y himl3 determined t h e demulsibilities of t h e original oils or t h e oils after 238 hrs.’ insolation a n d of ,the latter after t h e y h a d been filtered through bone-black. T h e carbonization values of two of t h e filtered oils were also determined. The results are given in Table 11. It is plain t h a t oxidation caused a decided deterioration of .the oils, a n d t h a t a distinct improvement was effected b y shaking with bone-black a n d filtering soon thereafter. This is in agreement with t h e work of Schwarz a n d Marcusson,* who were able t o extract from oils certain resinous substances which, when heated t o 120’ in t h e air, blackened a n d were trans1 Bureau of Standards, Bull. 7 (1910). 370; Bureau of Standards, Technologic Paper 4 (1911). 4; THISJOURNAL, 3 (1911), 235, 813. 2 The expression “demulsification value” has been used b y Arnold Philip ( J . SOL.Chem. I n d . , 34 (1915), 700) t o denote the percentage of oil which separates in 24 hours. T h e word selected by Mr. Herschel is not only a shorter expression b u t refers t o a different unit. 3 There is in course of preparation a paper describing the apparatus and procedure for making this determination. 4 Z . angew. Chem., 26 A (1913). 385.
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
5 90
formed into asphalt t h a t was insoluble in benzene.' M A U M E N 6 NUMBERS-chiefly as a matter of interest t h e Maumen6 numbers of t h e oils, before a n d after exposure t o sunlight for 438 hours, were determined. Fifty-gram samples were mixed with I O cc. of concentrated sulfuric acid a n d stirred vigorously until no further rise of temperature was observed. The oilacid mixture was contained in a I O O cc. tall beaker surrounded with a thick layer of cotton batting in a larger beaker. A simple mechanical stirrer, using t h e laboratory blast for motive power, was employed. Temperatures were read on an Anschutz thermometer having a range of j o o a n d graduated t o 0.2'. The results obtained appear in Table 11. The Maumenk number, like t h e heat of bromination and t h e iodine number, is supposed t o be a measure of t h e degree of unsaturation of a n oil, The nondrying oils give lower values t h a n the drying oils.2 IODINE NU;\rBERs-Kissling long ago pointed out t h a t for different oils t h e resinification number (carbonization value) may vary much more t h a n t h e
-
Increase in Carbonpation z-b-77rne
.
o f Heating
T~rnpe~atur~-25O~C. v3
Vol. 8, NO. 7
TABLE11-DETERXINATIONS ON ORIGINAL AND OXIDIZED OILS Demulsihility
ORIGINALOILS No. 1 No. 2 S o . 3
&$~o~~~a~[;h "O ~ ~ ~ m C , e t & o80,.,132
7,3 0.1:
360 0.3: ,,I
OXIDIZEDOILS Untreated Filtered No. 1 No. 2 KO. 3 h'o. 1 No, 2 32 45 200.,4620 20,00 0.63 10.Sz 8,8
2z:io 3i;!,o ;!,:io t,"::" i::zo
I ~ ~ i ~ ; ~ ~ o:::3; m p ~ ) 31.5 29.8
30.3
20.4
19.1
20.6
0, .I 3, 4.
163 0, .,5, 5,
: :: ; ::;
. . . . ....
of this Bureau. His results (Table 11) confirm t h e statement of Kissling. Oils I and 2 show a slightly greater drop in the iodine number t h a n does Oil 3, b u t t h e difference is perhaps not great enough t o be worthy of special comment. E F F E C T OF T H E T I H E O F H E A T I N G U P O N T H E P E R C E N T -
A G E O F CARBOKIZATIOK
In order t o learn whether t h e percentage of carbonization is directly proportional t o t h e time of heating, or whether t h e reaction is progressively more or less rapid, a series of determinations was made upon t h e three oils under investigation. Ten-gram samples were heated t o 2 j 0 O for one, two, etc., up t o
Increase in Curbontj.ot/bn
Temperature T r n e o f Heating
3 Hours
'lu
h'laumen& and iodine number^.^ T h e iodine numbers of Oils I , z and 3, and of the same oils after 438 hours' insolation, were determined b y J. H. Bower,
seven hours, t h e insoluble precipitate being thrown dom-n and determined in t h e usual way. T h e results are shown in Table I11 and are plotted in Fig. 11.
1 For other d a t a having a bearing upon this general subject, including the formation of asphalt, see Schwarz and Schluter, Chem.-Ztg., 36 (1911). 1907, 145; 413-5; Holde and Eickmann, Mitt. kgl. ~~aterialprilfu?zgsamt, cf. Z. angew. Chem., 20 (1907), 1263, 1293; Southcombe, J . Sot. Chem. I n d . , 30 (1911), 261-4: Zaloziecki and Zelinski. 8th Internat. Cong. A p p l . Chem., 10 (1912), 335-341; Chem.-Ztg., 36 (1912), 1305; Gurwitsch, Z . Kolloide, 11, 17; Petroleum. 3, 65-8; Chem. Zentu,, 83, I1 (1912). 1792. 2 For interesting d a t a on variations and irregularities in t h e iodine numbers of certain oils, see Jenkins, J . Sod. Chem. I d . , 16 (1897), 193-4; Archbutt, I b i d . , 6 (1886). 312; Ballantyne, Ibid., 10 (1891), 32; Lewkowitsch, "Chem. Techn. a n d Anal. of Fats, etc.," 5th Ed., Vol. I. pp. 484-5. 8 Chem-Ztg., 30 (1906), 932-.3.
TABLEI I I - v A R I . 4 T I O N
IX CARBOlrIZA'TIOK
O F HEATIXG TO Carbonization (Hrs.) 1 2 0.10 Oil No. I . . . . . . . , . , . , . . , , , , 0 . 0 3 o i l i Y o . 2 , . . . . . . . . . . . . . . . . , 0.04 0.10 o i l N o . 3 . . . . . . . . . . . . . . . . . . 0.04 0.16
(PERCENT.4GES)
250" 3 0.14 0.17 0.30
4 0.34 0.37 0.60
5 0.51 0.54 1.02
WITH
6 0.83 0.94 1.37
TIME
7 1.26 1.25 2.01
The time was counted from the moment t h e heating current was turned on. About half an hour was required t o heat t h e b a t h t o 2 j o o , b u t long before this temperature mas reached, oxidation began.
,411 t h e oils gave practically t h e same results on heating for one hour, b u t b y t h e end of two hours Oil 3 already showed a decided deviation from t h e other two. This deviation became increasingly greater as t h e period of heating was lengthened, while Oils 2 a n d 3 kept close together throughout. The ordinary physical a n d chemical tests gave no indication t h a t t h e oils would behave so differently on heating. AS Kantorowicz says, " t h e slight differences in t h e asphalt content of cylinder oils in contrast with t h e great differences in practice, would make it appear advisable t o test oils quantitatively as t o their ability t o form new asphalt under definite conditions."' The curves show t h a t t h e conditions obtaining a t elevated temperatures effect a grouping of t h e oils different from t h a t due t o oxidation a t ordinary t e m peratures in sunlight, if we consider only t h e gains in weight a n d in acidity. The carbonization values of t h e oxidized oils will be discussed further on. I t is important, from t h e standpoint of routine laboratory testing, t o learn whether or not t w o oils t h a t yield nearly t h e same percentages of carbonized matter when heated for 2 or 3 hrs. remain equally close together if heated for a longer time. Eight oils of well known brands were heated for 2 1 / 2 , 3 1 j 2 a n d 4 I j z hrs. a n d t h e insoluble matter was determined as usual. A a n d C were light a n d heavy grades of TABLE I\'-CARBONIZATION OF EIGHTSPECIAL OILS HEATED T O 250' FOR DIFFERENTPERIODSOF TIME Flash Fire Percentage carbonization when heated for 0 il point point 21/? hrs. 31/2 hrs. 41/2 hrs. A , . . . . . . . 190; 245 O 0.08 0.23 0.48 250° 0.04 B . , . . . . . . 225 0.14 0.36 C . . . . . . . . 235; 2800 0.02 0.05 0.03 D . . . . . . . . 230 265' Trace Trace Trace 2000 0.40 0.98 1.86 2000 0.47 1.00 2.12 G . . . . . . . . 185; 230' 0.35 0.62 1.90 H . . . . . . . . 160 1900 0.70 1.38 2.45
t h e same brand. B a n d D were light and heavy grades of a second brand. E, F a n d H were from t h e same company, while G was a fourth brand. The d a t a obtained are given in Table I V a n d are plotted in Fig. 111. The d a t a confirm t h e results found for Oils I t o 3, a n d do not call, for a n y special comment. I n saying this it must be understood t h a t t h e a m o u n t of carbonized matter formed by heating t o 2 j o o for only one hour is disregarded. EFFECT
OF
59 1
T H E J O U R N A L O F I N D U S T R I A L A Y D EAVGINEERING C H E M I S T R Y
July, 1916
DIFFERENT
TEMPERATURES
UPON
THE
CARBO%-IZATION' V A L U E
Just as t h e carbonization value depends upon t h e length of time t h e oil is heated, so also it must v a r y with t h e temperature. I n order t o determine t h e magnitude of t h e changes, a series of tests was made The a t temperatures varying from 230' t o 2 7 j ' . d a t a are given in Table V a n d are plotted in Fig. IV. TABLEV-INFLUEFCE
OF
Sample 230' NO. 1 . . . . . . . . . 0 . 1 0 A-0.2 . . . . . . . . 0 . 0 7 No. 3 . . . . . . . . . 0 . 1 3
TEMPERATURE UPOP THE CARBOXIZATION VALUE Carbonization value when heated to 240' 2.50' 26.5' 275' 0.11 0.14 0.72 1.59 0.09 0.17 0.84 1.96 0.16 0.30 1.03 2.32
The time of heating, in each series, was 3 hrs. T h e curves are of t h e same general form as those showing the effect of lengthening t h e period of heating, although Chem.-Ztg., 37 (1913). 1594-5.
in this series of determinations no two of t h e m lie close together a t t h e highest temperatures. The eight oils, A t o H, which were tested as a f u r t h e i check upon t h e influence of t h e time of heating, were carbonized for 2 l / 2 hrs. a t each of three temperatures. Table VI gives t h e d a t a obtained. The corresponding curves are shown in Fig. V. It is interesting t o see TABLE VI-CARBONIZATION
OF
EIGHTSPECIAL OILS HEATEDTO DIFFERENT
TEIIPERATURES
Temp. OilA B 250 O . . . . . . . . . . . 0.08 0 . 0 4 260 '. . . . . . . . . . . . 0 . 4 3 0 . 4 0 270 . . . . . . . . . . . . 1 . 1 8 0.81
C D 0 . 0 2 Traces 0.11 Traces 0 . 4 5 0.31
E
F
G
H
0.40 0.47 0.35 0.70 1 . 1 1 1 . 2 2 0 . 7 7 1.33 2.02 2 . 5 1 1 . 6 8 2.54
t h a t Oil D, which gave only traces of carbonized m a t ter even when heated for 4l/2 hrs. a t 2 5 0 ° , a n d which in this series of tests did not carbonize t o a n y extent a t 260°, shows a sudden increase in insoluble matter a t 270'. T h e curves of t h e other oils are of t h e expected form. They are a further justification of t h e conclusion already drawn, t h a t t h e greater t h e carbonization value is a t zjo', t h e more rapidly does it increase when t h e oil is heated t o a higher temperature. GENERAL CONSIDERATIONS
Experience has shown t h a t , while it is easy t o obtain concordant results in determining t h e carbonization values of "good" oils, it is an entirely different matter when t h e percentage of precipitate is in t h e neighborhood of one per cent or more. It is believed t h a t this is not due t o unequal heating of t h e flasks in different positions in t h e b a t h , a n d it is certainly not due t o differences in t h e thickness of t h e flasks. The most reasonable explanation appears t o be t h a t occasional particles of foreign matter, such as metal or rust, act catalytically, giving t h e portion of oil in which t h e y happen t o be a s t a r t over t h e others. An interesting case bearing upon this came t o light in testing a sample in which there were numerous black particles. T h e bottle was left undisturbed for 24 hrs. t o allow these t o settle a n d t h e oil was t h e n tested. The value found was 0.91. A few weeks later, t h e bottle having been untouched meanwhile, t h e carbonization value was 0 . 5 5 , a figure t h a t agreed closely with t h e value for other samples of t h e same brand. This experience emphasizes t h e need of taking every precaution i n sampling, as well as in testing t h e oil. I n this connection may be mentioned t h e work of Schluter,l who found t h a t in most of t h e cylinder deposits examined b y him, t h e trouble did not lie i n t h e quality of t h e oil used, b u t was caused b y sand a n d other foreign matter accidentally introduced or carelessly left in t h e engine cylinders, etc. I t m a y be well t o repeat, parenthetically, t h e statement t h a t there is no direct connection between t h e loss by evaporation when an oil is heated and t h e percentage of carbonized matter formed a t t h e same time.2 Because this statement has been questioned, though not in print, it may be well t o give t h e following d a t a showing t h a t this is t r u e not only for t h e same, b u t also for different oils. Chem.-Ztg., 37 (1913), 221-3. 2 Bureau of Standards, Techaologic Paper 4 (1911), 12. THIS JOURNAL, 3 (1911), 815.
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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 E E M I S T R Y
TABLE1'11-SHOWING
INDEPENDENCE OF CARBONIZATION VALUE A N D O N HEATINGTO 250° Oil No. 1 No. 2 No. 3 Evaporation in 3 hrs., per cent . . . . . . . . . . . . . 17.3 19.3 19.6 23.9 21.0 22.5 Corresponding carbonization. per cent . . . . . . 0.16 0.14 0.17 0.18 0.30 0.30 Evaporation in 5 hrs., per cent. ....... . . . . . 21.3 24.3 27.3 30.7 26.8 29.5 Corresponding carbcnization, per c e n t . . . . . . 0 . 5 1 0.51 0.56 0.S5 1.09 1.05
EVAPORATION Loss
It so happens t h a t these oils have carbonization values t h a t increase as t h e flash and fire points become lower. T h a t this is accidental can be seen from Table V I I I , which gives d a t a on a few oils recently tested, and shows t h a t t h e flash and fire points are also independent of t h e carbonization value: TABI,~: VIII-SNOWING INDEPENDENCE OF CARBONIZATION VALUEAND THE F L A 5 H AND FIREP O I N T S
.
Flash point. C ...... . 125' 165O 190' 195' 195O 200° 200' 20S0 225O Fire point, C .... . . . . . 205O 205O 220' 235' 235O 240' 250° 245' 2 6 5 O Carbonization per cent 0.42 0.41 0.06 0 . 2 9 0.16 1.05 0.22 0.39 0.06
SUiSMABY
In order t o determine whether there is any close connection between t h e rate of oxidation of automobile oils when exposed t o sunlight and air, and their carbonization values when heated .to comparatively high temperatures, a s t u d y was made of three brands of oil. T h e gains in weight a.nd in acidity and t h e increase in t h e carbonization value were determined. a t frequent short intervals. I n t h e first t w o of these tests, two of t h e oils showed nearly identical gains, t h e third differing quite noticea.bly. I n t h e carbonization tes.t t h e values for t h e three oils were quite far a p a r t , Of minor importance were determinations of t h e demulsibility, t h e iodine number and t h e Maurnen6 number. T h e effect of oxidation was t o increase the tendency t o form eniulsions with mater. T h e iodine numbers were lower and Maurnen6 numbers higher for t h e oxidized t h a n for the original oils. T h e changes in the carbonization values caused b y heating t h e above three oils and eight others t o 2 5 0 ' for different lengths of time were then studied, a s well as t h e changes caused by heating t o different temperatures for three hours. It was found t h a t in both cases the greater t h e carbonization value at first, t h e more rapidly did i t increase as t h e temperature was raised or t h e time of heating extended. I n other words, a n oil which has a low carbonization value if heated t o 2 5 0 ' for two or three hours a n d a n oil showing a somewhat higher value under ,the same conditions will be farther and farther apart as t h e conditions become more strenuous. The carbonization value of a n oil is coming t o be recognized as a valuable criterion in routine testing, and methods for its determination are finding their way into text-books, as re11 as into the journals. Most of these methods prescribe heating t h e oil for many hours, b u t it seems, from t h e work described above, t h a t this is unnecessary. I n most cases heating for 2'/2 hrs. is sufficient and has t h e advantage of permitting two runs in a working day, with t h e necessary interval of a n hour or more for t h e b a t h t o cool. Of far greater a n d indeed, of vital importance, is t h e exercise of extreme care in taking a n d preserving samples, as well as in testing them.
V O ~8, . NO. 7
A s t u d y of all t h e d a t a obtained shows t h a t there is no direct proportionality, b u t only a rough parallelism, between t h e results of t h e different tests described above. I n conclusion, i t is shown t h a t t h e carbonization value is independent of the flash and fire points, and of t h e evaporation loss on heating. B E R ~ A OF U STANDARDS, WASHIIIGION
K JELDAHL MODIFICATION FOR DETERMINATION OF NITROGEN IN NI?RO SUBSTITUTION COMPOUNDS~ By W. C. COPE Received March 21, 1916
T h e Bureau of Mines has received numerous requests for information in regard t o t h e determination of nitrogen in nitro substitution compounds, and as many requests have come from skilled chemists it appears t h a t t h e information usually a t hand lacks details which are necessary t o obtain trustworthy results. T h e following method has been evolved from t h e work of Kjeldahl,2 G ~ n n i n g J, ~ o d l b a ~ e r a, ~n d others, a n d has given good results on a variety of compounds over a period of a year a n d half, and since several members of the laboratory force have obtained consistent results it is believed t h a t the method is suitable for general analytical work. 11E T H OD
Weigh accurately about 0 . jooo g. of t h e nitro substitution compound and place in a joo cc. longnecked Kjeldahl digestion flask. Then a d d 30 cc. sulfuric acid (96 per cent), containing 2 g. of salicylic acid, a n d dissolve t h e nitro compound b y rotating t h e flask, or by heating over a steam b a t h if necessary. After cooling, add z g. ol' zinc dust in small portions at a time, continually rotating t h e flask a n d cooling t o prevent heating above room temperature. After all t h e zinc has been added, rotate t h e flask a t I O or 1 5 min. intervals for about t o 2 hrs. and then let s t a n d over night a t room temperature. Heat t h e flask very gently over a small flame until evolution of fumes has ceased (requirigg usually t o 2 hrs.), then bring t o boiling and continue boiling for I'/* t o 2 hrs.; cool slightly and a d d I g. of yellow mercuric oxide (HgO) and boil I t o 1'/2 hrs. longer. Now a d d , after cooIing, 7 . 5 g. potassium sulfate (K2S04) and I O cc. more sulfuric acid, and boil 1 1 / ~ t o 2 hrs. longer. If the solution is clear and practically colorless t h e digestion is complete; if not, a d d I g. more potassium sulfate and boil f o r t o I hr. longer. Cool t h e liquid in the flask and a d d 2 5 0 cc. distilled water t o dissolve cake formed; then add 2 j cc. potassium sulfide solution (80 g. per liter of distilled water), I g. granulated zinc, and 8 5 t o go cc. sodium hydroxide solution ( 7 j o g. per liter of distilled water), completing t h e determination as is usual for all modifications of the method. 5 2 8
4
Published b y permission of the Director, U. S. Bureau of Mines J. Kjeldahl, Z. anal. Chem., Bd 22 (1883). 366 Gunning. Ibtd., Bd. 28 (1889). 188. M. Jodlbauer, Chem. Zentr. (3 F.), Ed. 17, 433.
