EDITOR'S COLUMN years, since, on the average, they decrease in emf a t the r a t e of 20 to 40 microvolts per year. Routine B u r e a u measurements of u n s a t u r a t e d cells were discontinued as of J u n e 30, 1961. T h e Bureau, however, does compare u n s a t u r a t e d cells for public utilities and other agencies conducting operations t h a t require direct B u r e a u services. T h e Bureau also continues to conduct referee tests. A report of calibration is issued on cells submitted to the B u r e a u for emf measurement. T h e report gives the results of the measurement and, if pertinent, t h e physical con dition of the cell. I n terms of absolute measure ments, the N a t i o n a l Reference Group of s t a n d a r d cells is stable to within 0.12, /xv./yr. or better, and this stability m a y be approached by other s a t u r a t e d s t a n d a r d cells. In terms of the Bureau's records of cells submitted for calibration, the average changes in emf range be tween —1.2 /xv./yr. and + 1 . 2 , μν./yr. I n recent years, the n u m b e r of s a t u r a t e d cells submitted to the N a tional Bureau of S t a n d a r d s for checking has increased significantly. Within the last 10 years, for ex ample, the number has increased from 50 cells per y e a r to more t h a n 800, indicating t h a t a large number of s t a n d a r d s laboratories throughout the country m a i n t a i n groups of sat urated cells t h a t can in t u r n be used to check u n s a t u r a t e d cells. U n s a t u r a t e d cells not intended for uses t h a t would necessitate compar ison at the Bureau should be sent to the manufacturer for checking, or to a s t a n d a r d s laboratory equipped with a group or groups of saturated cells having emfs known in terms of the national standard. In this way, traceability of values and units to the N a t i o n a l B u r e a u of S t a n d a r d s can be maintained. F u r t h e r information on the cali bration of standard cells may be found in the article, " M e a s u r e m e n t of S t a n d a r d Cells," Nat. Bur. Std. (U.S.), Tech. News Bull. 48, N o . 1, J a n . 1964.
table model centrifuges to meet your analytical needs From the most complete line of table model centrifuges . . . four Clay-Adams models de signed for industrial and chemical laboratories . . . all are shock-mounted precision instruments engineered and manufactured to assure years of superior performance.
c-ADAMS ANALYTICAL: For micro and semi-
a-ADAMS SAFEGUARD CENTRIFUGE-ANGLE AND STANDARD HEADS: A multi-purpose, basic instrument for labs with heavy work loads . , . accommodates any one of four standard or four angle heads . . . useful for all com mon separations and special analytic pro cedures . . . holds tubes of 15 ml. or less and up to 50 ml. . . . dial rheostat control pro vides variable R P M and R C F range.
d-ADAMS MICRO-CHEMISTRY: F o r m i c r o - a n
micro separations . . . accommodates six tubes (5 or 3 ml.) . . . also adaptable for 2 and 0.5 ml. tubes . . . angle-head effi ciency . . . compact, portable, requires minimum table space . . . provides fixed 3,400 RPM speed. alytic separations of organic and inorganic precipitates . . . eight-place angle head ac commodates 1, 0.5, and 0.25 ml. glass or plastic tubes . . . provides high fixed speed (13,500 RPM-15,500 RCF) . . . high RCF assures separation of particles of similar specific gravities . . . complete, automatic stop in 60 seconds.
b-ADAMS SAFETY HEAD: For all commonly performed precipitate separations . . . adaptable for micro and semi-micro anal yses . . . six-tube capacity (15 ml. or less) . . . angle head provides fast, efficient centrifugation . . . variable R P M and R C F . . . compact, light and portable.
Available from your dealer
Clay-Adams New York 1 0 , Ν . Υ.
Circle No. 31 on Readers' Service Card
LOOMIS IDEAL PRESS ^ for
FORMING KBr PELLETS • Pellets for X-Ray a n d Other Analysis S h o w n — 2 0 Ton Lab Press with New
Plastic, Ceramic a n d M e t a l Forming • General Lab Use
Compact
Power Unit and accurate
handwheel and
50
adjustment. ton
models.
Also
30
Heating
platens o p t i o n a l .
Accessories for temperature, pressure, extrusion testing units, etc. are available for all models
WRITE
FOR
BULLETIN —DEPT.
A
* For better results use Loomis Λ VA" precision x-ray pellet die
LOOMIS ENGINEERING & MFG. CO.
22 RT. 4 6
CApitol 6-8660
CALDWELL, NEW JERSEY
Circle No. 122 on Readers' Service Card V O L . 3 6 , N O . 2 , FEBRUARY
1964
·
129
A
