CountonPPO (the fluor — hathas. — everything) And here's proof... At its optimal concentration (4g /liter toluene), PPO costs just 1.6 cents per 15 m! sample. The new PBD derivatives are used at concentrations of 7-8q/ liter of toluene, resulting tn nearly twice the cost for little or no increase in performance! And, even when your samples are highly quenched and contain only minimal activity, PPO plus a little of our new spectrum shifter, bis-MSB, is still the logical primary scintillator to use. PPO is extremely soluble in most common solvents, even at low temperatures. In fact, it is the most readily soluble of all common primary scintillators. A product of our Pilot Chemicals Division, it is available from NEN along with virtually any other scintillator you require. Call collect for prompt, personal service, and ask for a copy of our complete brochure on liquid scintillation fluors. Price schedule: NEF-901 PPO $8/25g $30/100g $135/500g NewEngland Nuclear 575 Albany Street, Boston, Mass. 02118 Telex: 094-6582 Phone (617) 426-7311 In Europe: NEN Chemicals GmbH., Siemensstrasse I, 6072 Dreieichenhain, bei Frankfurt (Main), Germany Telex: 4-14393 1260 ' Tel: (06103) 3353 . SCIENCE, VOL. 158