The Improved Welch CATHETOMETER
the ANALYST'S column L.T.
VI7"ITH
Rapid Leveling — Fine Adjustment — Graduations Engine Divided for U n i f o r m i t y and Accuracy
Hallett, Editor
T H E development
• Φ ~Φ Φ Φ
of t h e
midget-type selenium rectifier used in television, missiles, a n d other " p e a n u t " electronic assem blies, selenium h a s become critically i m p o r t a n t . Formerly t h e principal uses were in t h e glass, ceramic, chemical, pigment, rubber, a n d stainless steel industries. Selenium is a paradoxical element. According t o J. D . Sargent 1 , it h a s been defined a s : " e i t h e r a metal or a nonmetal, a conductor or non conductor, amorphous or crystalline, colorant or decolorant, a n d a h y d r o genator or dehydrogenator." Daniel S. Turner, geological con sultant, Denver Club Building, Denver, Colo., in a communication to us entitled "Selenium, a Geologi cal Sleeper," notes t h a t t h e demand for selenium is estimated a t twice the present supply. T h e electronic industry, for example, which uses this element in producing rectifier and photoelectric tubes, consumes more t h a n one half of current production. Total demand for sele nium now probably exceeds 2,000,000 pounds a year. Although silicon a n d germanium rectifiers are used often in place of selenium, n o satisfactory substitute has been found for m a n y applica tions of selenium. At present there is little hope t h a t current sources of supply can catch u p with rocketing demands. No Commercial Deposits. Except as a by-product of t h e base m e t a l industry, n o naturally occurring commercial reserves of selenium are known. T h e increasing demand for selenium is pushing t h e price u p . I t h a s been a s high a s eight times t h a t of uranium. Now it is about equivalent t o U 3 0 8 for similar p e r cent tenor. Selenium is a mysterious element Sargent. J. D., "Selenium D a t a , " TJ. S. Bur eau of Mines, Circ. 7715, April 1955, p. 1.
Vertical range 100 cm Vernier reading to 0 . 0 5 mm Working distance 45 cm to infinity Magnification 12xat 45 cm—8 χ at infinity Level sensitive to 50 seconds
This Cathetometer is intended f o r measurements a n d o b servations in both industrial a n d educational l a b o r a t o r i e s wherever a n inexpensive instrument o f g o o d precision is n e e d e d . It is r i g i d l y constructed a n d every essential a d justment can b e m a d e simply a n d positively. The telescope is mounted horizontally on a c a r r i a g e which m a y b e moved up or d o w n or around the 3 0 - m m vertical rod. A tangent-screw adjustment permits precise leveling a n d a sensitive elevation adjustment is i n c o r p o r a t e d in the c a r r i a g e . A n a u x i l i a r y level in the base g r e a t l y acceler ates the leveling process. No. 0 8 A — E a c h $ 2 4 7 . 5 0 Full-length Plastic Cover a n d Set o f Instructions included. Wriie for descriptive circular.
W. M. WELCH SCIENTIFIC COMPANY Division
of W. M. Welch Manufacturing
Company
ESTABLISHED 1 8 8 0 1515 Sedgwick St., Depl. A-1, CHICAGO 10, I L L , U.S.A No. 68A
NEW
Manufacturers of Scientific Instruments and Laboratories Apparatus
TEM£a
FLASK HEATER
a / r e a d / proved by "in-use" tests and nationwide acceptance Here's the g r e a t l y i m p r o v e d flask heater with inter c h a n g e a b l e M o n e l mesh baskets that p e r f e c t l y " n e s t " your flasks . . . a n d let y o u use several sizes in the same unit! Radiates heat uniformly t o lower h a l f o f flask . . . mini mizes " b u m p i n g . " Easily r e p l a c e a b l e heating element eliminates time a n d use losses. N o fabrics t o become s h o d d y , s a t u r a t e d , or w o r n . Heating chamber sealed t o contain accidental s p i l l a g e . . . easily c l e a n e d . TEMCO Flask Heater is r u g g e d l y built with stainless steel a n d b u f f e d aluminum double-case construction. W e l l - v e n t i l a t e d . . . p e r f o r a t e d outer shell never t o o hot t o handle . . . t a b l e - t o p h e a t - p r o t e c t e d attached support b r a c k e t . M a y b e used with control unit shown b e l o w , o r with other makes o f controllers. T w o models f o r a l l p o p u l a r flask sizes: $22.50 and $34.50. Several different flask sizes can be used in this unit N e w Controller f o r e x t r e m e l y f i n e control o f flask heaters Model 700 Temcometer power input controller of " o f f - o n " type with completely stepless control and short time cycle. Permits excep tionally fine selection, close holding of desired temperature. Com pensates automatically for wide fluctuations in voltase. Ideal com panion unit for TEMCO Flask Heaters and other makes of heaters and mantles. Price complete with power and connecting cords, $20.85. Quality is assured under the TEMCO label. Write- or complete data and name of nearest dealer.
THERMO ELECTRIC MANUFACTURING C O . 478 HUFF ST., DUBUQUE, IOWA For further information, circle number 69 A-2 on Readers' Service Card, page 99 A VOL.
2 9 , N O . 9 , SEPTEMBER
1957
·
6 9 A
