The advantages of combining the old with the new are to your advantage. Not change for the sake of change. But adding new strengths to the old ones you've come to rely on at Arthur H.Thomas. A computerized inventory system, for example, added to the good things we've always offered. Pre-tested products. Always in stock. Shipment within 24 hours on over 90% of orders. Concerned objectivity about your needs. Knowledgeable salesmen with the ability to be of real help. All combined with good old-fashioned Arthur H.Thomas reliability and dependability. • We think it's a hard-to-beat combination. Our customers do, too. If you haven't had the opportunity to order from Arthur H. Thomas recently, perhaps it's time to give us another look. And choose your next purchase

from our large, diversified, always available selection of reliable, tested laboratory apparatus and reagents. Arthur H.Thomas. Company, Vine Street at Third, Philadelphia, Pa. 19105.

A R T H U R H .

THOMAS C O M P A N Y

The S200 Thomas Pollution Trace Oven—an alternative to a S2.000 analyzer. If your job is identifying and measuring trace amounts of metallic particles in the environment, here's a simple, reliable, fast—and inexpensive method. With the Thomas Trace Oven you concentrate rather than dilute when you dissolve your sample. You don't end up with metal concentrations that take a $2,000 multi-phasic instrument to measure. You get a narrow dry ring, right on the original sampler filter, with the dissolved metals so concentrated you can cut the ring into sectors and measure individual metals by proven, quantitative color techniques. Sensitivity and specificity are comparable to much more expensive instrumental methods. Special Trace Oven Reagent Kit available. Circle 201 on Reader Service Card for details. The Thomas-Hoover Melting Point Apparatus gets it all together

—approved methods with better uniformity and operator ease. Get fast, reproducible, plant-to-plant, shift-to-shift results using official U.S.P. and similar capillary-in-oil methods with this self-contained unit. Not a heating block. And it's really all together-heater, stirrer, thermometer, thermometer reader and lamp, and all controls in one compact, safely untippable unit. Not an improvised "Christmas tree" assembly that vibrates out of alignment, breaking thermometers and spilling hot oil. Our periscopic thermometer reader brings the magnified image of thermometer reading point just an eye-motion above the sample observation port. Eliminates the sit, stand and squint cycle. Circle 202 on Reader Service Card for details.

Little-known facts make Thomas pH electrodes respond faster, reduce errors. All pH electrodes are not alike. Thomas electrodes give you fast, unwavering response because of the low resistance of their glass bulbs. But strength is not sacrificed to do this. Thomas electrodes are rugged. In our popular combination-type electrodes, we provide an extremely short path between the glass sensor and the reference junction. This avoids overshooting of titration endpoints, and gives rapid detection of pH change in process control. Shielding in all types is positive and complete—Thomas electrodes can be used in grounded and ungrounded systems. The Thomas line includes electrodes for small volumes, high temperature, high pH, pipeline or tank installation. Connector fits jack of most pH meters directly or through adapters. Circle 200 on Reader Service Card for details.

A R T H U R H.

THOMAS C O M P A N Y

VINE STREET AT THIRD · P.O. BOX 779 · PHILADELPHIA. PA. 19105