1NDUSTRIAL AXD ENGINEERING CHEMISTRY
392
OF METHYL BROMIDE DETERMINATIONS BY TABLE I. ACCURACY THE METHOD DESCRIBED
MeBr Used Gram 0.0480 0.0355a 0.0333 0.0312 0,0299 0.02930 0.0288@ 0,0278 0,0244 0.0145 0,0125 0.0079 0.0065
Normality of NaiSiOs 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.05 0.1 0.05 0.05
MeBr Found Gram 0.0474 0.0352 0.0326 0.0304 0.0294 0,0286 0,0279 0.0271 0.0238 0,0140 0.0126 0.0077 0.0066
Error
%
-1.2
-0.8 -2.1 -2.6 -1.7
-2.4 -3.1 -2 5 -2.5 -3.5 +0.8 -2..5
-3.5 per cent. Samples ranged from 0.0480 to 0.0065 gram. The reproducibility and accuracy of these results are probably much greater than the reproducibility of fumigating conditions. The quantity of methyl bromide used in fumigating is usually about 2 pounds for each 1000 cubic feet of space, which is equivalent to approximately 0.064 gram in a 2-liter sample of air. Consequently the range of samples analyzed probably coincides roughly with that encountered in actual practice. The use of more dilute thiosulfate would permit the determination of smaller samples.
Literature Cited
+l.5 Av. -1.;
0 R u n a i t h 2-liter sampling bulb between sample and saponification apparatus.
The results are given in Table I. The average error of 13 analyses is -1.7 per cent; the greatest individual error is
VOL. 10, N O . 7
(1) Don- Chemical Co., private communication. (2) Glaser, Deut. 2. ges. gerichtl. MecZ., 12,470-4 (1928). (3) Leipert and Watslawek, 2. anal. Chem., 38,113-16 (1934). (4) Meulen, r a n der, Chem. Weekblad, 28, 82 (1931).
(5) Nuckolls, Underwriters' Laboratories' Rept., Mise. Hazard No. 2375 (November 13, 1933). RECEIVED May 6, 1938.
A Modification of the Markley Melting Point Apparatus MILTON S. SCHECHTER AND H. L. HALLER Bureau of Entomology and Plant Quarantine, U. S. Department of .4griculture, Washington, D. C.
T
HE Markley melting point apparatus (1) has been used
satisfactorily for some time in this laboratory. The apparatus is essentially a large Thiele tube in which very rapid circulation of liquid is obtained through the use of an efficient stirrer, ensuring rapid interchange of heat between
the liquid, the melting point tube, and the thermometer. However, the usual methods of attaching the melting point tube to the thermometer have proved very troublesome. The use of a small rubber band or a small spring requires the removal of the thermometer from the bath, the attachment of the melting point tube, and the replacement of the thermometer in the bath each time that a reading is to be taken. Furthermore, there is always the danger of breaking the thermometer . The apparatus was therefore modified by sealing to i t two side arms of 3-mm. tubing in such a position and a t such an angle that, when melting point tubes are inserted, their lower ends come in contact with the thermometer bulb. The side tubes should be long enough so that their open ends will come above the highest level to which the liquid in the apparatus will rise during its operation. It is advantageous to have the angle between the side tubes and the vertical as small as possible, about 35 degrees. Each side arm is wound with a short piece of wire (such as No. 25 chrome1 A), the end of which is bent over the opening in such a manner as to press the melting point tube against the inner surface of the side-arm tube. The melting point tube will thus be held steady and the lower end will be pressed in contact with the front of the thermometer bulb. This modification of the apparatus simplifies the determination of melting points, since the melting point tubes can readily be inserted or withdrawn through the side arms. The thermometer may be left permanently in place by inserting it through a cork having a 90-degree sector cut out so that the cork Kill not block part of the thermometer scale. A commercial grade of chlorinated diphenyl, as recommended by Dr. Markley in a private communication, has been found to be a satisfactory substitute for the usual sulfuric acid-potassium sulfate mixture.
Literature Cited (1) Markley, K S., IND. ENG CHEX, Anal Ed., 6, 475 (1934). FRONT VIEW
SIDE V I E W
RECEIVED .\pril 26. 1938.
