GROW AEROBIC AND ANAEROBIC CULTURES IN THE

GYROTORY® INCUBATOR SHAKER

A controlled temperature incubator with continuous shaking action. Agitation speed variable from 140 to 400 rpm. Triple-eccentric-shaft stabilizing system dis­tributes positive rotary motion to every flask on the 18" χ 30" platform. Cool, quiet, smooth-running.

, . ' M O D E L G25. C ι r c u l a t i n g heated air, the fully insulated un i t p rov ides constant tem­perature, ambi-ient to 60° C , ± V 2 ° C Other speed r anges , and connections for gassing avail­able. Adapt­able for tubes, b o t t l e s , a n d other glassware.

Overall Dimensions: 2 5 " long χ 4 1 " wide χ 2 9 V i " deep.

UNCONDITIONAL ONE YEAR WARRANTY

Write for Catalog G25-A11

NEW BRUNSWICK SCIENTIFIC CO., INC.

P.O. BOX 606, NEW BRUNSWICK, NEW JERSEY

Circle No. 159 on Readers' Service Card

FOR:

Glassblowing

and other

tasks

obscured by

a dazzling

yellow flame

The selective f i l te r ing lenses in PARR Glassblowers' Gog­gles block out the object ion­able y e l l o w g lare a lways present in g lasswork ing oper­at ions. They transmit only a trace of ye l low l ight w i thou t seriously reducing the inten­sity of red and other colors in the visible spectrum. Ava i l ­ab le in l i g h t w e i g h t safety f rames, also in a cl ip-on style, each complete w i t h case.

Order from any Parr Dealer, or write direct for Spec. 4200.

P A R R INSTRUMENT CO. MOLINE, ILLINOIS

CONTRIBUTED ARTICLES

Polarographic Determination of Titanium in Tan­talum and Niobium Concentrates and Ores . . . 1 836 D. K. Banerjee, C. C. Budke, and F. D. Miller

Polarographic Determination of rV,N'-Ethylenedigly-cine and Nitrilotriacetic Acid in (Ethylenedinitrilo)-tetracetic Acid R. B. LeBlanc 1 840

Direct Quantitative Diffractometric Analysis . . . . 1842 P. P. Williams

Determination of Blood Urea with p-Dimethylamino-benzaldehyde H.H.Brown 1844

Extraction and Determination of Thorium from Sulfate and Phosphate Solutions with Tri-n-octylphosphine O x i d e W. J. Ross and J. C. White 1 8 4 7

Determination and Stabilization of Reduced Ascorbic Acid in Extracts from Plant Materials . Η. Τ. Freebairn 1 850

Ion Exchange Membranes in Coulometry 1 852 S. W. Feldberg and C. E. Bricker

Determination of Organic Nitro Compounds by Con-trolled-Potential Coulometry J. M. Kruse 1854

Application of Constant Current Potentiometry to Nonaqueous Titrations of Weak Acids 1857 Irving Shain and G. R. Svoboda

Determination of p-Phenylenedilithium by Potentio-metric Titration with Cerium(IV) Nitrate Solution. . 1860 A . F. Clifford and R. R. Olsen

2,4,6-Tripyridyl-s-triazine as Reagent for Iron. Determination of Iron in Limestone, Silicates, and Refractories 1862 P. F. Collins, Harvey Diehl, and G. F. Smith

Zirconium Analysis by Production Control Quantom-e t e r C. L. Easlerday 1 8 6 7

Amperometric Determination of Tin with Cupferron 1868 S. S. Yamamura, J. E. Rein, and G. L. Booman

lodometric Method for Determination of Persulfates 1 870 Nagi Wahba, M . F. El Asmar, and M . M . El Sadr

Determination of Chlorine Dioxide in Treated Surface W a t e r s M . A . Post and W. A . Moore 1 8 7 2

Direct Karl Fischer Determination of Water in Vinyl Ethers Lucien Barnes, Jr., and M . S. Pawlak 1 8 7 5

Selected Triphenylmethane Dyes as Acid-Base indicators in Glacial Acetic Acid 1876 O. W. Koiling and McC. L. Smith

Circle No. 86 on Readers' Service Card

6 A • ANALYTICAL CHEMISTRY

PARR Glassblowers'

GOGGLES

P R E C I S I O N L A B O R A T O R Y A P P A R A T U S