INSTRUMENTATION
RESEARCH AND PILOT PLANT EQUIPMENT
for DRYING and CALCINING
Gas Fired Continuous Rotary Dryer
The gas fired continuous rotary dryer—pictured above — is used for drying ores, chemical salts, sand, clays, fertilizers and various other materials that can be brought into direct contact with the products of combustion. Inlet gas temperatures to 900° F.; velocities up to 600 R.P.M. using propane or other bottled gas. Approximately 2 4 " wide; 5'6" long; 2 ' 9 " high. For either purchase or rental.
Steam Heated Continuous Rotary Dryer Gas Fired Rotary Continuous Combination Calciner and Cooler Electrically Heated Rotary Continuous Combination Calciner and Cooler Direct Fired Rotary Kiln Steam Jacketed Batch Dryer (with Rotary Sweep)
Parker and Adams [ANAL. CHEM.
Get full details. Write for Bulletin No. 117 today!
T H E C. O. B A R T L E T T & S N O W C O . 6210
HARVARD
AVENUE
·
CLEVELAND
5.
OHIO
For further information, circle number ββ A-1 on Readers' Service Card, page 99 A
First choice for washing and soaking pipets . .. glassware!
NALGENE* PIPET JARS with NEW NON-TIP
BASES
The resiliency of Nalgene* Polyethylene sharply reduces breakage and the new base design practically eliminates tipping accidents. New non-tip base is molded into jar (not welded) and assures steadier, longer life with perfect bond. NALGENE PIPET JARS
come in standard sizes as listed below; special lengths made on order. ' 'Brand SIZE
A
Β
C
D
Ε
F
Dim. Inches Nominal
5x8
614x9
5x18
6>/ 2 xl8
6>/2x27
6VSx36
No. in Case
12
12
6
6
6
6
Each
9.50
10.50
11.50
13.50
17.50
20.50
Ask your dealer for catalog N a m e f o r Nalge
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Polyethylene
ware.
the NALGE CO. Inc. R O C H E S T E R
2 .
N E W
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Discount: Less 1 0 % in case lots.
WORLD'S
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OF POLYETHYLENE
LABORATORY
For further information, circle number 80 A-2 on Readers' Service Card, page 99 A 8 0
A
·
ANALYTICAL
rent value, up to a maximum current of the order of 100 Ma. In the work cited above, the scanning current was obtained from a constant voltage source of high value. Regulation and measurement of the current were ob tained by using known resistors in series with the voltage source. A more recent development uses a vacuum tube circuit to supply the scanning current and a microammeter to measure the current. The pH meter is connected to the electrode under examination and to the reference half cell. Change in voltage of the selected electrode is indicated continuously by the p H meter. Measurements are made man ually by adjusting the scanning cur rent and recording the corresponding voltage and current values. A series of such points at successively increas ing currents is obtained and plotted. The resulting curve can be interpreted to give considerable analytical in formation.
CHEMISTRY
WARE!
28, 828 (1956)] point out certain ad vantages of the current scanning method in the analysis of phenylenediamines. Automatic Potentiometric Polarography. Adams has developed auto matic equipment to carry out current scanning polarography. His equip ment uses the Model 7664 p H meter with a Speedomax recorder to record the current voltage curves (see Figure 2). The scanning current is controlled by a motor-driven potentiometer which regulates the output current through an impedance-converting unit em ploying a transistor. The resulting current output shows good linearity with time. He has made such meas urements with the dropping mercury electrode. Chronopotentiometry. In chronopotentiometry a constant current is applied to a pair of electrodes in a cell. One electrode is selected for examination and may be a pool of mercury or a platinum plate. After the circuit is closed, the potential of this electrode increases with time. Change in voltage is observed with the pH meter. The meter is connected to the electrode in question and to a third electrode, a reference half cell in the solution. The plot of changing electrode volt age with time has a characteristic sigmoid form when a substance which can undergo a reaction at the electrode is present in the solution. The time that is required for the voltage value to pass through the limits defined by the substance is termed the transition time. The square root of the transi-
