ANALYTICAL EDITION
346
ated tube. All titrations are best controlled by the use of the lowest stopcock. This buret delivers approximately 26 drops per ml. and is suitable for work with blood and urine in addition to the more general analytical procedures. The graduation interval is 0.02 ml., but readings are easily possible to 0.01 ml. Because of the relatively small bore of the graduated t,ube, some time must be allowed for afterflow if the tube has been emptied rapidly and readings of greatest accuracy are desired. This seldom requires a total of more than 1.6 to 2 minutes, and ordinarily most of this drainage will have taken place during the time necessary for the withdrawal of the last few drops. Two of these burets have been made a t moderate cost by E. Machlett & Son of Long Island City, N. Y., the first of which has been in constant use over a period of 2 years. They are of rugged construction and excellent workmanship. The calibration is highly accurate, the volumes being adjusted well within the tolerances required by the U. S. Bureau
Vol. 4,No. 3
of Standards for measuring pipets. sions of the buret are as follows:
The approximate dimen-
Total length.. ................................... Length of graduated main tube from 0 to 5 m l . . ..... Height of side tube with bulbs.. . . . . . . . . . . . . . . . . . . . Distance from 5-ml. graduation to point of curved tip Length of tip below stopcock.. .................... Diameter of graduated main tube (outside). . . . . . . . . . Diameter of bulbs (outside). .......................
.
Total capacity., . , , ............................. Capacity of graduated main t u b e . . . . . . . . . . . . . . . . . . . Capacity of single bulb.. .......................... Subdivisions,, ...................................
Cm.
60 38 23 15 4
0.8 1.4
MI. 17 5 3 0.02
These dimensions give a small unit convenient both for general laboratory use and for certain specialized procedures. Manipulation is rapid and easy, total capacity large, and accuracy adequate for exact measurements. RECEIVED January 11, 1932. Published with the approval of the Director of the West Virginia Agricultural Experiment Station, as Scientific Paper 106.
Pressure Control with Automatic Liquid-Leveling Device J. V. VAUGHEN,E. I. du Pont de Nemours & Co., Wilmington, Del.
THERE
is often a need in the laboratory for a device which will automatically control liquid levels in the leveling bulbs of gasometers and combustion pipets and in mercury reservoirs in such a way as to give constant pressure or c o n s t a n t l i q u i d flow. Figure 1 represents a variation of the a r r a n g e m e n t used by Stone ( 1 ) that has been used in this laboratory f o r m a i n t a i n i n g a constant flow of mercury to displace liquids at a constant rate into a r e a c t i o n vessel. T h e mercury reservoir, C, is s u s p e n d e d b y a suitable spring, B, which lifts the r e s e r v o i r a distance e q u a l to the fall in mercury level in the bulb when m e r c u r y flows out. The s p r i n g and reservoir are matched by measuring the e l o n g a t i o n , X , of the spring with a load of 100 cc. of m e r c u r y . The appropriate diameter, D, of the reservoir is then calculated according to the formula D = 2
stance two springs 27 em. long were used together to support a mercury reservoir. Together these springs stretched 6.8 cm. for 100 cc. of mercury. The calculated diameter of the reservoir was 4.32 em. The reservoir was made with a diameter of 4.5 em. and further adjustment of the apparatus was accomplished by shortening the spring. A volume of 200 to 300 cc. of mercury could be emptied from the reservoir with a change in mercury level of less than 3 mm. I n applying this scheme to the maintenance of constant pressure in gasometers and combustion pipets with leveling bottles, the following equation gives the relationship between the radius, r, of the gasometer or combustion pipet, the radius, R, of the leveling bottle, and the elongation, X, of the spring, for a volume, Ti, of confining liquid:
I n one instance a leveling bottle for a gas-combustion pipet was suspended by two springs 42 cm. long. They elongated 8.0 em. with a load of 100 cc. of mercury. Since the diameter of the pipet was 4.8 em., the leveling bulb should measure 7.2 em. LITERATURE CITED (1)
Stone, Engineering, 100, 554 (1915).
RECEIVEDFebruary 16, 1932. Contribution 91 from the Experimental Station, E. I. d u Pont de Nemours & Company.
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WORLDPOTASHPRODUCTION. According to the estimate of the general director of the Kaliwerke Aschersleben, reported The reservoir is made of to the Department of Commerce by the trade commissioner at t u b i n g of approximately Berlin, potash salts representing 1,457,400 metric tons of potash this diameter, and further were produced in the world in 1931 In 1930 world production of potash was 2,018,000 tons, and in 1929, 2,118,000 tons. OF m a t c h i n g is accomplished Germany is first in volume of potash produced, with 964,000 LEVELINGDEVICE by c h a n g i n g the length of tons; France (Alsace) second with 340,000 tons' the United States third with 60,000 tons; and then Poland, kpain, Russia, the spring. in the order named. A decline from over 1,300,000 tons in 1930 Brass springs have been found more suitable than steel is shown in German production, and a drop of 16 per cent for ones, and they are generally made by winding No. 16 B. & S. the first five months of 1932 over the corresponding period in brass wire on a 0.25-inch (0.62-em.) mandrel. I n one in- 1931, in sales of German potash.
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