INDUSTRIAL Ah’D ENGINEERING CHEiWSTRY
September, 1927
preferable crystalline state by reheating and subsequent rapid cooling. It was subsequently noted that Ardagh and Davidson’ cooled a lubricant on an aluminum sheet and that this practice is established in other laboratories. AGING-AS indicated above, aging plays a n important part in determining the final quality of a lubricant. Some compositions set from a sticky semifluid to a smooth grease in 10 days. Others, suitable a t first, caked out in periods ranging from 6 to 12 m o n t h . I n general, the sinoked sheet lubricants possessed sufficient body when fresh from the oven, and retained a desirable consistency until used upsay, 12 to 24 months. I n the lubricants containing much rubber (high-vacuum type), though not in the case of the lighter lubricants, pale crepe requires a definite aging period. Para requires a long aging period. Latex more nearly resembles Para. Lubrication of Stopcocks
There are many methods of lubricating a stopcock, and not all are entirely efficacious. A method familiar to many acquainted with high-vacuum technic may be recommended. The lubricant is applied in two parallel longitudinal streaks, one on either side of the plug and away from the bore. The streaks should be as thin as possible, and contain only enough lubricant to flow entirely around the plug. The lubricant so placed, the plug is held above a soft Bunsen flame, so that the grease just melts to form a smooth ridge of semicircular cross section. The key is allowed to cool and then carefully inserted into the barrel so that the bores of plug and 4
C a n . Chem. M e f . , 9, 137 (1925).
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barrel coincide. The plug is pressed downward into place, with little, if any, turning, the lubricant forming V’s on either side of bore and pressing out all air films until it has flowed smoothly around the entire grinding. A stopcock lubricated with a high-vacuum or heavy grease should be turned slowly and smoothly with a very slight pressure of the plug into the barrel. A good high-vacuum lubricant presents enough resistance to turning to require the use of two hands for nice manipulation, one to support the bottom of the cock against strain and the other to press slightly and turn. If a stopcock is finely ground and carefully lubricated with a type of lubricant suitable for high vacua, it will occasion the worker in high vacua no difficulty because of stopcock leaks. This laboratory has had several systems of such cocks hold a vacuum for 2 years, as indicated by a barometric manometer (accurate to 0.2 mm.) which showed no pressure change. An apparatus in constant use, containing paraffin hydrocarbon gases whose vapor pressures were 0.0001 mm. or less at - 210’ C., and involving seventeen plain stopcocks without mercury seals, consistently failed to show pressure increases greater than 0.0001 to 0.0005 mm. over 2 to 4 weeks time, as measured by a LMcLeod gage. Well-ground, well-lubricated stopcocks do not stick. Such stopcocks have been known to stand idle over periods of several years without exhibiting any tendency to “freeze.” It is believed that the disfavor with which stopcocks are held by many investigators is not warranted, since varied experience has clearly shown that a well-ground cock properly lubricated is an entirely satisfactory and extremely handy unit of apparatus in the great majority of gas investigations.
Determination of Isopropyl Alcohol in Presence of Acetone, and of Methylethylketone in Presence of Secondary Butyl Alcohol’ By H. A. Cassar S T A N D A R D OIL C O M P A N Y O F
N INVESTIGATIKG the oxidation of isopropyl alcohol to acetone, analytical methods were lacking which would quickly and accurately determine isopropyl alcohol in a mixture of the alcohol plus its oxidation product, acetone. I t was finally found that by oxidizing the alcohol quantitatively to acetone by means of chromic acid solutions and titrating back the excess chromic acid the isopropyl alcohol could be readily determined in less than an hour. ,4 similar method, a t slightly different concentrations, was found to hold for secondary butyl alcohol in the presence of methylethylketone; but whereas acetone could be determined in the presence of isopropyl alcohol by Messinger’s well-known method,* applying a correction of 1 to 2 per cent for the isopropyl alcohol present, it was not possible to determine methy!ethylketone in the presence of secondary butyl alcohol without a considerable modification of the method. This method when applied directly to methylethylketone under certain conditions gives results that are constantly 10.5 per cent too high, over a wide range of alkali and ketone concentrations, and hence methylethylketone can be easily and quickly determined by the iodine method. This method
I
1 2
Received May 4 , 1927. Ber., 21, 3366 (1888); Goodwin, J . A m . Chem Soc., 42, 39 (1920).
NEWJERSEY,
ELIZABETH,
N. J
is not quite independent of the presence of secondary butyl alcohol; and a mixture of 50 per cent methylethylketone and 50 per cent secondary butyl alcohol gives results which are 2.5 per cent too high, over and above the 10.5 per cent. The procedure will therefore be to determine the secondary butyl alcohol content by means of the dichromate oxidation method and correct the final methylethylketone value found by a quantity which will not) exceed 3 per cent (Figure 1). The probable reason for the high value found by the iodine method of determining methylethylketone is that the two following reactions occur simultaneously:
+ +
+ + +
C H ~ C H Z C O C H ~ 312 3NaOH CHI3 CHXHZCOOH C H ~ C H Z C O C H ~ 512 4NaOH 2CHI3 f CHaCOOH
+ 3NaI + 2H20 + 4NaI + 3H20
I n one case six atoms of iodine are used up, and in the other case ten. The methods herein described have been used on commercial samples for more than a year, and the results have always checked with the results of careful fractional distillation. Isopropyl Alcohol and Acetone Mixture
A quantity of the isopropyl alcohol and acetone mixture containing about 15 grams of isopropyl alcohol is accurately
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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weighed out and made up to 500 cc. Twenty-five cubic centimeters are pipetted out into 100 cc. of 45 per cent (by weight) sulfuric acid contained in a glass-stoppered 250-cc. Erlenmeyer flask and 50 cc. of 1 N sodium dichromate solution are added from a buret, a few drops at a time a t first, with careful shaking until the solution turns green before adding more. The addition of dichromate should take about 10 minutes, and the temperature should not go above 25" C. The stoppered flask is then put aside for a half hour, and then the contents are made up to exactly 500 cc. Twenty-five cubic centimeters are pipetted out
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