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I-VD USTRIAL A,YD ENGINEERING CHEMISTRY
cc. and but 0.3 cc. of titrating solution was required to give all the end-point phenomena. From a similar procedure Curve B was produced by titrating dilute phosphoric acid with sodium hydroxide. This curve has the two characteristic flex points. Curve C resulted when sodium carbonate was titrated with hydrochloric acid and gives two flex points.
Vol. 19, No. G
Perhaps the greatest advantage of this electrode system is the fact that titrations involving oxidation and reduction reactions may be performed in the same apparatus. Hence, any laboratory having electrometric apparatus may, by adding an auxiliary electrode with the polarizing circuit, perform a number of titrations ordinarily requiring the hydrogen electrode.
Comparison of Sensitivity of Various Tests for Methanol' By Leslie 0. Wright U. S. INTERNAL REVENUEBUREAU, BRANCH LABORATORY, BUFFALO, N. Y.
EARLY all of the numerous proposed tests for Reagents which were used to condense the formaldehyde methanol depend upon the same principle-oxidation to a color, with reasons for their rejection, are as follows: of the methanol present to formaldehyde, to formic REAGENTS WHY DISCARDED acid, and in some of them to carbon dioxide and water. Less sensitive than rosaniline Fuchsin bisulfite Georgia and Morale9 report that the oxidation to formic Can be used only in concentrated acid Morphine sulfate Not sensitive acid or carbon dioxide is unsatisfactory, so that the generally Poor keeping qualities z$&,hine accepted method is by oxidation to formaldehyde and the Rosaniline was found to be best suited for the detection subsequent detection of this product by a suitable reagent. of formaldehyde because it The- adequacy of the test may be made into a stable, implies, fir& the efficiency A survey has been made of the various methods procolorless (or nearly so) reof the oxidation of methanol, posed for detection of methanol. Oxidation with poagent. It is very sensitive, and second, the use of a tassium permanganate to form formaldehyde, which a n d a n easily recognized sensitive reagent t o detect in turn is detected by reduced rosaniline solution, is violet color is produced with formaldehyde by producing the method adopted. formaldehyde. a compound giving an easily It is recommended for standard work, where comThus, after trying various recognized color. For this parisons are desired, that solutions of 5 per cent alcohol reagents, both for oxidation second reaction a rosanilinebelused, and that other standard conditions, as outand for the condensation of sulfurous acid reagent was lined, prevail. For qualitative work, samples may be the formaldehyde to a color, used. run as received. If a positive test is found, glycerol t h o s e g i v e n below, based The purpose of this work or pectin may be present and the sample must then upon the work of C h a ~ i n , ~ was to study the degree of E l v o ~ eand , ~ Deniges5 were be distilled and again tested. sensitivity, best concentrafound to be best suited. tion of alcohol, other reagents for the oxidation of Reagents the methanol, and the elimination of various interfering substances such as glycerol. (1) Potussium Permangunate. Dissolve 3 grams of potassium
N
Preliminary Experiments
As oxidizing agents, hydrogen peroxide, chromic acid, ammonium persulfate, hot copper spiral, and potassium permanganate were tried, but all except potassium permanganate were rejected as unsatisfactory. The chromic acid came next in the order of desirable oxidizing agents, but gave a green color when no methanol was present (due to reduction of chromium by any organic matter present), and this color is undesirable because a violet color produced by small amounts of methanol may be obscured. While oxidation of methanol takes place more rapidly with chromic acid as the oxidizing agent, the test is not so sensitive and hence not 60 desirable as oxidation with potassium permanganate. The copper spiral was discarded because a positive test was obtained with ethyl alcohol. Hydrogen peroxide apparently has no effect on methanol and was therefore rejected. Ammonium persulfate was not sufficiently sensitive and gave a color for a negative result. These experiments confirmed those of Georgia and hlorales.* 1 Received February 28, 1927. Printed by permission of the Prohibition Unit, U. s. Internal Revenue Bureau. * THISJOURNAL, 18, 304 (1926).
permanganate in 100 cc. of water previously distilled over potassium permanganate, and containing 15 cc. of phosphoric acid. By using water previously distilled from potassium permanganate solution, this reagent can be kept for a long time. (2) Oxalic Acid Solution. Dissolve 5 grams of oxalic acid in a solution made by diluting 50 cc. of sulfuric acid (1.84) to 100 cc. (3) Schiff's Reagent (modified). Dissolve 0.2 gram of rosaniline, or a n equivalent weight of its salt, in 120 cc. of hot water, cool, and add this to a solution of 2 grams sodium bisulfite in 20 cc. of water. Finally add 2 cc. of concentrated hydrochloric acid and dilute the whole t o 200 cc. This solution should become colorless or nearly so after standing. If it is protected from the air no deterioration results. A very pure rosaniline base was used in these tests, but a product of lesser purity may be used, giving a somewhat colored reagent, which is, nevertheless, satisfactory.
Determination Place 2 cc. of the sample in a test tube and add 1 cc. of potassium permanganate solution. Allow t o stand for 10 minutes; decolorize by adding 1 cc. of the oxalic solution, followed by 2 cc. of the modified Schiff's reagent and mix. The solution must be mixed thoroughly. If methanol is present a violet color is developed. With traces of methanol the color is not 4
6
THIS ] O E R N A L , 13, 543 (1921). I b i d . , 9, 295 (1917). C o n 9 t . r e n d . , 160, 823 (1910).
I S D C S T R I A L A S D ESGINEERI,VG CHEMISTRY
June, 192T
developed for a n hour. Glycerol or p,ectin in suficient amounts will produce a like color and for t h a t reason if a positive reaction is obtained the test should be made on the distillate. No specific alcoholic percentage is recommended, for while the test is somewhat more sensitive in dilute solutions, it is sufficiently sensitive in a n y concentration for qualitative work, as is shown in Table I. Table I-Color
Developed m i t h Various Amounts of Methanol in Alcohol
ETHANOL B Y \'OI.CME
ETHYL
1
a
ALCOHOL,P E R 10
25
CEKT BY
50
VOLCME
75
92
Peu c e n t 0 00
0 002: 0 005 0 01 0 03 0 0.5 0 08 0 10
0--So 1-Very '-Slight
color s l l b h t color
3-Fair 4-GOOd
color color
color
C o n d i t i o n s Necessary for S t a n d a r d Work
ALCOHVL C'OXCEXTRATIOS-AS is shown in Table I. for a gi7 en amount of methanol the color developed was very much stronger with weak alcoholic liquors than with stronger ones. The color is usually developed in a few minutes, but in the case of only 0.01 per cent methanol the maximum color was deleloped only after standing for 2 hours. Thus, while this test is best run on 5 per cent solutions or less, it nil1 show positive results with 95 per cent alcohol, providing the methanol content is correspondingly higher. I n reducing a sample of alcohol from 95 per cent to 5 per cent, the methanol content is also reduced and any advantage of greater sensitivity is counterbalanced. XMOVSTOF SULFURIC -4crD-It was found that the amount of sulfuric acid could be somewhat reduced and by this method the sensitivity of the test increased with no interference from other substances, but since the tesl, is sufficiently sensitive this IS not recommended. By using one-half the amount of acid (oxalic solution) a sample containing only 0.000048 cc. of methanol in 2 cc. of a 5 per cent alcoholic solution gave a positive test, while the blank gave no color using the same amount of acid. However, this reduction is not recommended inasmuch as this degree of sensitivity is not necessary. TIME OF OSIDATIO?;-~a separate set of standard solutions containing 0.03 per cent methanol and 1 per cent ethyl, the time of oxidation was increased from 1 minute to 8 minutes, and the samples showed only a small difference between the color produced after oxidation for 1 minute and that oxidized for 8 minutes. To cover all cases of high percentages of alcohol and all variations in temperature, hoJvever. the oxidation should be allowed to continue for a t least 10 minutes. The same test was run using 10 per cent ethyl and 0.03 per cent methanol, with the results showing niuch less color than in the former set using only 1 per cent ethyl, but the same small difference in color between that sample oxidized for 1 minute and those oxidized for 8 minutes as in the previous case. TEMPERATURE-Astudy was made of the effect of variations in temperature of the solution during oxidation. The samples run contained 0.1 per cent methanol and 5 per cent ethyl alcohol. The temperatures were 3", 20", 60-70", and 100" C. The results showed that variations in temperature had very little effect on oxidation except in the last case, which developed less color than the other samples This, it 1s believed, is due to the continued oxidation of the formaldehyde to formic acid. Using the same strength of methanol, a study was made of temperature variations on the formaldehyde-condensation-to-color solution, a t 3" and 100" C. At 3" C. no appreciable color developed and evidently no
731
condensation takes place at this Ion- temperature. dfter raising to 20 O C., however, the color developed normally. After a color is formed, if the solution is raised to 100" C. the violet color is discharged. Variations of normal room temperature have no effect on intensity of color formed. T e s t s i n Presence of Glycerol
The only way found for eliminating a pojitive test in the absence of methanol and the presence of glycerol or pectin mas by distillation, but glycerol was found t o give only one-tenth of the amount of color given by an equivalent volume of methanol. Thus, when a sample has been reduced from 40 per cent to 5 per cent alcohol, the interference is only noticed when 4 per cent or more of glycerol is present in the original sample, this being a higher percentage than is usual. Several workers found that apple juice gave a positive reaction with most methods. This, it is believed, is due to the fact that pectin is present in fruits id the forrii of unstable methyl esters of pectic acid. The following tests were made to determine h o fruit ~ juices could be analyzed in order to eliminate a positive reaction in the absence of methanol: The first was run on a dilute solution of pectin direct; the second, by distilling 150 cc. of diluted pectin t o 100 cc.; the third, by distilling the diluted pectin solution containing sodium hydroxide solution, and the last. by using sodium carbonate. In the first and last two cases a positive reaction was obtained. It is, therefore, necessary that the sample be distilled slowly from a solution free from alkali. Reaction
The mechanism of the reaction involved is probably as follo\vs:
H~N(II) -C-=SH?
SHKh
+ H2O
HiXH c1 Rosaniline HCl Red Color H
A
J
SHJHC1 Colorless
HNH C1 Violet Color Q u a n t i t a t i v e Tests
Methods based upon physical constants are not applicable to the estimation of small quantities of methanol in alcohol because of the small margin of difference in physical properties. This method, however by colorimetric comparison.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
752
is applicable to the estimation of even the smallest amounts of methanol. Using 5 per cent ethyl alcohol solution, the standards recommended for comparisons are: 0.00, 0.01, 0.05, 0.1, 0.2, and 0.4per cent of methanol. It is quite necessary that standard conditions prevail-namely, (1) 5 per cent alcohol; (2) the same kind and amount of reagents; (3) 10 minutes for oxidation with potassium permanganate; (4) uniform temperature (room temperature is satisfactory,
Vol. 19, No. 6
since both samples and standards will be at whatever temperature prevails); (5) length of time (20 minutes) in making comparisons after the addition of the modified Schiff reagent. Acknowledgment
The writer is indebted to John F. Williams of this laboratory and to E. Raymond Riegel of the University of Buffalo for advice and assistance.
Flat Luminous Flames' By D. S. C h a m b e r l i n and W.
E. Thrun2
LEHIGHUNIVBRSITY, BWIHLEHEM, PA.
A f o r m u l a has been adapted f r o m the Poiseuille An o r d i n a r y differential I T T L E has been ree q u a t i o n f o r the flow of gases through a n a r r o w slit f l o w m e t e r was constructed corded concerning the as exhibited in the lava tip. A comparison Of t h t flow with a pressure gage attached burning of combustible gases in secondary air from of different gases f r o m such tips in an i g n i t e d and an as shown in ~i~~~ 2. unignited condition detelops various f a c t o r s that are slotted tips. Several investis t u d i e d in this paper. The arms of the meter were g a t o r ~have ~ ~ ~made , ~ investiThe shape and size of the lava-tipped flame w a s kept Parallel by two Or three gations on the various types of luminous flames a s t h e y s t u d i e d by photographic methods. The differences in gas flow f r o m the tips in ignited and u n i g n i t e d conthe burn from lava tips in the was controlled by a ditions are discussed. It w a s f o u n d that the wider b o l t t h a t could be screwed shape of fishtails, batwings, vertically through a nut. The slotted tips d i d not conform to the same principles as etc., but such data on the nut being soldered to the gage those of n a r r o w e r slotted tips. shape and size of flames, flow holder, a slight motion of the rates, temperatures, and presbolt quickly adjusted the levels sures that can be applied t o the laws for the flow of gases to the desired zero. At high rates of gas flow a movement of 1.0 cm. corresDonded to a change in gas flow of 0.03 liter Der minute: are rather incomplete. a t the lower rates of flow i.0 cm. movement corresponded t o a I n the fundamental study of flat luminous flames, account change in flow of 0.68 liter per minute, must be taken of the size and shape of tip used. Lava Pressure-Rate Relations tips as employed in the older methods of gas lighting were The data given in Table I were taken from a number of series of experiments that were performed under constant conditions. The gas escaping through a tip was lighted and the flow rate adjusted for a definite flowmeter reading. The pressure was then read. The flame was then blown out I and the gas allowed to escape into the room. ilfter a 3minute interval the pressure and flow rate were again observed. On igniting the gas the initial readings were checked. These data were plotted and the results showed that:
L
yEkie,I"dti^^^
7-1I
I I I
Section through slot Figure 1-Lava
I
Side view
Tip
1-The pressure-rate curves were not straight lines. \Then the gas was burning, the curve approached a straight line more nearly than when the jet was unignited. 2-The difference in pressure of burning and unignited jets rose with increasing flow rates t o a maximum and then receded. It receded approximately t o a zero value, as was found in several other runs. These runs are not shown.
used in the determinations described herein. They are made of steatite, a magnesium silicate. In the green state steatite is soft and therefore can be made into any desired form by turning, milling, and grinding. The tips are then fired to a temperature of about 1400" C. Figure 1 shows the construction of a typical lava tip. Gas and A p p a r a t u s Used
Natural gas with an analysis of 71.2 CHI, 23.3 CzHt,, 4.7 NZ,and 0.8 per cent COSwas used in this work. This gas was delivered a t a uniform pressure from a gas holder. 1
Received January 4, 1926; revised manuscript received March 23,
1927.
* Columbian 4
6
Carbon Fellow, Lehigh University. Matake Kurokawa, J . SOC.Chem. I n d . ( J a Q a n ) , a@, 139 (1926). Ring. "Treatise on Gas." Bur. Mines, Bull. 192.
f Figure 2-Flowmeter
w i t h Pressure Gage
In the investigation of the factors that controlled these flames, it was found quite generally that there was a maximum point in the flicker of the flame,6its shape, and tempera6
Chamherlin and Thrun, Gas Age-Record, 57, 41, 52 (1926).
