INDUSTRIAL AND ENGINEERING CHEMISTRY
334
TABLE 11. RECOVERY OF SICOTINE FROM APPLE FOLIAGE ISample consisted of 50 leaf disks, 3.81 cm. in diameter, t o which was added i h e indicated amount of nicotine. One milliliter of nicotine solution (nicotine eulfate with 1 per cent corn, Karo, sirup) = 0.58 mg. of nicotine.] Nicotine Recovered Nicotine Added
'MI.
.Mn,
n
n
lt.0 20.0 20.0
3.60 11.20 11.20
Mg.
70
0 5.54 11.23 11.16
99 100 100
evaporation to about 100 ml. can he avoided. Table I1 shows some results obtained by this procedure. Whenever it is necessary to keep foliage for some time before analysis, the sample should he placed in a jar with 50 ml. of hydrochloric acid solution (1 to 9). I n this way samples h a r e been kept for 10 weeks with no 105s in nicotine.
YOI,. I O , YO.0
Summary A method for determining the small quantities of nicotine found on sprayed apples is presented. I t s novelty consists essentially in n-ashing nicotine from the fruit with a mixture of aqueous sodium hydroxide solution and ethylene dichloride, from which the nicotine is recovered, then distilled, and precipitated with silicotungstic acid. The results are accurate to 0.1 mg. over the range 0 to 12 mg. of nicotine on a 1-kg. sample. The method applies to hoth water-soluhle and water-insoluble nicotine insecticides.
Literature Cited 11) .Issor. Official Agr, Chem., Offirial a n d Tetitarix-e Slethotls, 4th ed., pp. 60-1 (193.5). REfTAYED
.kpril 22. 1937.
A Simplified and Portable McLeod Gage EARL W. FLOSDORF, LJni+ersity of Penns,l\ania. Philadelphia. Pa.
V
ARIOUS modifications of the McLeod ( 3 ) gage have
been proposed; perhaps the most common uses a low degree of vacuum on the atmospheric side to allow the mercury to be withdrawn from the bulb (1). To cause the mercury either to enter or leave the bulb, the present gage utilizes a metal swivel (2) that bears all the weight of the gage. A reading may be made in 2 to 3 seconds; the gage is compact, uses a minimal quantity of mercury, and is portable. Sudden changes of pressure do not affect the gage, whether it is under vacuum or not. I n Figure 1 the gage is shown diagrammatically in position R for reading, and (in broken lines) when turned to position P for acquiring the pressure of the system to be measured. For pressures above 0.001 mm., in order that the gage may be turned on swivel S , heavy-walled rubber tubing free from sulfur and talc is satisfactory for connection to the vacuum system at point A . For lower pressures a ground joint is
c
used tu permit turning the gage on thp swivel, and glass tubing is brought froni point d to point B , where it is passed out through the back of the metal case. The vacuum connection is attached a t B , in the center of the swivel axis, by a glass-to-metal ground joint, so that all rubber connections are avoided. With either device, the gage may be turned very rapidly in making a reading Tvith no danger of breaking and may also be easily disconnected and rendered portable. Figure 2 is a side view, ,homing details of the swivel. I n position PI which is not exactly horizontal, the mercury will drain completely into bulb C. A constriction at point D prevents the mercury from traveling too rapidly into and out of the capillaries, so that the gage may be swung very rapidly to and from posiF I G U R E 2 . SIMPLItion R. The diameter of bulb C is such FIED GAGE that when a pressure reading is made, Side view showing swivel, case, etc. the mercury in the right-hand capillary always comes to the top line, irrespective of whether or not themercury is high or low in the center capillary. The safety trap, E , permits the portable gage to be carried while full of mercury without loss of mercury even when inverted.
-4cknowledgment The author wishes t o acknowledge the helpful assistance of
J. D. Graham, the University of Pennsylvania glass blower, in the construction of these gages. Gages of several ranges may be obtained through the F. J. Stokes Machine Company, Olney, Philadelphia, Pa.
Literature Cited 11)Kaye, G. W. C., "High Vacua," p. 127, NeF York, Longmans,
'D f- ~3 I NPOSITION R SIMPLIFIED MCLEODGAGE F r o n t view showing t w o positiom
FIGVRE 1.
Green & Co., 1927. (2) Ibid., p. 129.
(3) McLeod, Phil. Mag., 47, 110 (1874). RECEIVED July 11 1938
