INSTRUMENTATION
N O W 160 L / M — W A S 140 L/NI W e l c h Duo-Seal No. 1402B 1 χ K M TORR
Now all Welch Duo-Seal® vacuum pumps have increased capacities. 33 y e a r s of vacuum p u m p design and manufacturing technology now enables W e l c h to sizably increase t h e capacity of all twostage Duo-Seal p u m p s . Size a n d appearance remains the same,but p u m p i n g speeds are increased u p t o 199Ό over previous models. In 1933, Welch pioneered t h e i n t e r n a l vane design of mechan ical vacuum p u m p s , long since p r o v e d to be t h e m o s t efficient, vibration-free, quiet, long lasting, trouble-free v a c u u m p u m p s ever m a r k e t e d . A l t h o u g h many o t h e r m a n u f a c t u r e r s h a v e switched to t h e internal v a n e design, only W e l c h produces Duo-Seal p u m p s , t h e p u m p s w i t h t h e p a t e n t e d DuoSeal gas discharge design, which eliminates r e p u m p i n g gases. Now, every two-stage Duo-Seal p u m p gives t h e added bonus of increased capacity, increases of u p to 19%, depending on t h e model which fits your needs. If you use vacuum, check on t h e Duo-Seal line. W e l c h m a i n t a i n s a staff of vacuum specialists w h o are a t your service to help you s e l e c t the right pump for your needs. W r i t e T h e W e l c h Scientific Company, 7300 N. Linder Ave., S k o k i e , I l l i n o i s 60076 o r c a l l 312/677-0600.
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ANALYTICAL CHEMISTRY
these measurements are very critical. In the double focussing, iron-free spec trometer, resolution of these fine lines requires a precision of 1 in 105 in the measurement of momentum. Elegant instrumentation involving reference to a bank of standard cells and a Tinsley potentiometer of 1 ^.V sensitivity achieves this precision. The potentiometric system is automated for pro gressive scanning. Electrical counting is supplemented by photographing the electron spectrum, with a television microscope for scanning the plates. We select a few random examples from this extensive series of researches. An outstanding example of the sensi tivity is illustrated by the electron spectrum of a large molecule like vita min B 1 2 which contains only one cobalt atom among 180 atoms of other ele ments. A 100 Â layer of B 1 2 thus contains very few cobalt atoms. Nevertheless cobalt is easily observed in the electron spectrum; furthermore, its value state can be determined. Cobalt appears as Co (3s) and Co(3p) along with lines from oxygen (O Is) nitrogen (N Is) and carbon (C Is). Insulin has a molecular weight of about 6000 and contains 51 amino acids with three disulfide bridges, two of which bind the peptide chains together. There is approximately one sulfur atom for every 140 other atoms. A good signal was recorded from sulfur, and the binding energy obtained was consistent with the value for simple disulfides. The relative intensity was in accordance with the known content of sulfur. The electron spectrum from carbon in solidified benzene using the freezing technique shows that the Is electron line has a width of 1.5 eV. Also four sharp and well defined peaks appear in the general binding energy region of 20 eV arising from the molecular orbitals. Any high school student these days can throw orbitals around with great ease. Here we have definite experimental measurements of high precision defining their nature and magnitude. This is a refreshing and most welcome contribution to this branch of metaphysics. We expect to devote a considerable part of the next six months in digesting this vast amount of information and in consulting some of the 299 references to similar work. Siegbahn is a revered name in the physics of X-rays. The earlier one, Manne, received the Nobel prize. Kai Siegbahn is well known in this country and much work on ESCA is going on here. Scientists in a dozen fields will be looking into its manifold applications for the next 20 years.
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