ATOM MODELS according to STUART AND BRIEGLEB ALANINE CHAIN
A t o m models according to S t u a r t a n d Briegleb give an exact picture of t h e actual spatial arrangement of a chemical compound. T h e models are spheres or ο voids with cut sur faces which can be joined together b y m e a n s of quick fas teners. Lateral surfaces are arranged in such a manner t h a t internuclear distances and effective radii of constructed molecules are reproduced in an enlargement of 1.5 χ 10 s with t h e correct valence angles and spatial arrangement. Carbon models, for example, have various shapes with differently arranged lateral surfaces depending upon t h e t y p e of bond. T h i r t y different structural units are presently available. Different colors are assigned to t h e various elements, which in clude hydrogen, carbon, oxygen, nitrogen, sulfur, phosphorus, silicon, fluorine, chlorine, bromine, and iodine. Hydrogen and halogen models are fitted with permanent quick fasteners. Other models are joined by quick snap-on fasteners. Sets include a small ejector tool for separating a t o m s a n d removing quick fasteners. Spring metal wedges are pressed into t h e slots of models used in double bonds to prevent rotation. T h e "hydrogen-bridge" is effected b y a new hook-and-eye arrangement t h a t enables larger angle shifts and permits t h e construction of strongly bound, hydrogenbridged molecules. S t u a r t and Briegleb molecular models are invaluable aids in studying three-dimensional arrangements of macro-
molecules, various types of steric effects, biochemical specific ity, geometrical and optical isomerism, tautomerism, reso nance, and other chemical phenomena. More detailed information is given in an 8-page, 3-color booklet. A 16-page booklet on the School Set of Atom Models is also available. Inquiries for kits to cover specialized needs are welcomed. Requirements for a single molecule for a given area of interest, such as peptides, sterols, or dyes, will be con sidered. No. AG302-80, I n i t i a l Set of 84 Pieces of 11 T y p e s of Atom Models, each $90.60 No. AC302-81, S u p p l e m e n t a r y Set of 40 Pieces of 13 Dif ferent Types, each $48.50 No. AC302-88, School Set of 44 Pieces of 9 Types of A t o m Models, each $43.50 A new data sheet. Molecules of Current Interest has just been published. It includes caffeine, cedrol, β-erythroidine, fulvalene, morphine, reserpine, san tonin, terrein, tetracycline, and trilobine. Alongside of the graphic formula of each molecule is listed the catalog numbers and prices of the components re quired to construct the model.
PARTICLE SIZE APPARATUS FOR SUB-SIEVE RANGE This instrument was designed to determine particle size within t h e range from 75 to 5 microns. However, if t h e top size is not greater t h a n 20 microns, the lower limit can ordinarily be ex tended to a b o u t 2 microns. T h e Gallenkamp particle size a p p a r a t u s is self-contained and comprises a sedimentation system, a receiving tank, and a direct-reading torsion balance—all mounted on a levelling stand. A powder of t h e material being measured is uniformly dispersed in a suitable liquid, a n d the particles are allowed to settle on the pan of a special torsion balance. T h e pan is suspended in clear liquid, and the weight indicated by t h e balance is not affected b y changes in density of t h e suspension. Because it is not necessary to extract, dry, and weigh the settled powder, no " b l a n k s " are required, and higher concentrations of dispersing agents can be used without applying correc tion factors. T h e time required to estimate size distribution of any powder is little longer t h a n the t i m e of sedimentation. T h e balance is sufficiently sensitive to permit t h e use of a very low concentration of solids, so t h a t sedimentation can take place under practically free-falling conditions. Another ad v a n t a g e is t h a t interference with t h e settling particles is negligible. Write for Descriptive
Literature.
No. AC368-51, G a l l e n k a m p P a r t i c l e Size D e t e r m i n a t i o n A p p a r a t u s , c o m p l e t e w i t h glassB, l e a d s for c o n n e c t i n g t o a 6-volt s u p p l y , a n d i n s t r u c t i o n s , e a c h $850.00
ARTHUR S. LaPINE and COMPANY
LAPINE
LABORATORY SUPPLIES ·
6001 SOUTH KNOX AVENUE CHICAGO 29. ILLINOIS. U.S.A.
EQUIPMENT · REAGENT AND INDUSTRIAL CHEMICALS
For further information, circle numbers 43A-1, 43 A-2, 43 A-3 43 A-4, 43 A-5 on Readers' Service Card, page 79 A
VOLUME
2 8, N O .
11, N O V E M B E R
1956
43 A
