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Selectacel ® ION EXCHANCE CELLULOSES for use in chromatographic columns New Selectacel Ion Exchange Cellu- loses have remarkable properties when used with ionic and colloidal materials of high molecular weight. Such applications include — • ENZYMES · LIPIDS • PROTEINS · NUCLEIC • HORMONES ACIDS These materials produce separations that far exceed what usually can be accomplished alone by ion exchange resins, chromatography, electro- chromatography, or electrophoresis. There are several kinds of Selectacel Ion Exchange Celluloses: ANION EXCHANGERS Type DEAE (Diethyl- aniinoethyl Cellulose) Grade Standard 20 40 Capacity meq/g 0.9 Separation and purification of proteins, peptides, enzymes, hormones and re- lated materials. Type ECTEOLA (Epichlorohydrin Grade Standard 20 40 Capacity meq/g 0.3 triethanolamine) Separation and purification of viruses. CATION EXCHANGERS Type CM ~arboxymethyl Cellulose) Grade Standard 20 40 Capacity meq/g 0.7 Weakly acidic—most effective at pH's slightly above 4. Type Ρ (Cellulose Phosphate) Grade Standard Capacity meq/g 0.9 Bifunctional — containing both strongly acidic and weakly acidic groups. Rela- tively high exchange capacities. Send for these new free Selectacel Reference Sheets today — no obli- gation of course. MAIL COUPON TODAY Carl Schleicher & Schuell Co. Keene, New Hampshire Department AC-4 Send FREE Selectacel Reference Sheets. NAME COMPANY ADDRESS. CITY STATE Selectacel is manufactured by Brown Company and exclusively packaged and distributed for laboratory use by S & S. REPORT FOR ANALYTICAL CHEMISTS The acid is introduced into the con- tainer in the molten form and is then allowed to freeze while the container is evacuated. The am- poule is lowered by a clock-work through a bath composed of two im- miscible liquids. The liquids are separately maintained at constant temperatures, the ux^per one about 25° C. above the melting point of the acid. Here the acid melts and is brought to a uniform tempera- ture. The lower bath is about 25° C. below the melting point. Very little heat transfer occurs be- tween the two liquids; conse- quently, there is a rather sharp dis- continuity of temperature at the interface between the two liquids. Thus, as the tip of the ampoule passes through the interface, freez- ing begins and under favorable con- ditions progresses through the liq- uid to produce a single crystal. The rate of freezing is about 1 cm. in 24 hours. Although many small crys- tals form in the tip at first, one or at most two or three will be favored in growth by the zig zag course of crystallization up the tip. Under most favorable conditions, only a single crystal face presents itself at the bottom of the ampoule proper. This face will be oriented parallel to the plane of temperature discon- tinuity in the surrounding bath. Impurities other than those, if any such exist, that form a solid solution with benzoic acid, tend to diffuse away from the solid-liquid interface and thus are concentrated in the last portion frozen. When freezing was complete in the work here described, the am- poule was inverted and the last por- tion frozen was allowed to melt and flow into one of the collecting bulbs, which was sealed off. The remain- der of the acid was then melted and the whole process repeated. The final product was considered to have an over-all purity that would not be distinguishable from ideal purity by any known method. It, therefore, was regarded as a suit- able standard for the highly precise acidimétrie measurement to be de- scribed later. Solvent Inclusions in Crystals Potassium biphthalate, likewise sodium oxalate and potassium cli- chromate, are substances which can be purified only by recrystallization from water· solutions, so far as is Figure 4. Single crystals of ammonium dihydrogen phosphate Reference Sheets on FREE Circle No. 91 on Readers' Service Card 26 A · ANALYTICAL CHEMISTRY
