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- 103 - (2) For a i r between square-edged rod electrodes, the d-c BDV i s e r r a t i c , p a r t l y because of dual valueis and p a r t l y because of a large decrease i n BDV with time of voltage application. The decrease i n BDV with ti i r e i s much greater 6+. high absolute humidity. The short-time BDV increases with increasing humidit.y and the long-time BDV decreases with increasing humidity. (3) In the design of equipment to operate at high d-c voltages i t i s even more important to use electrodes free of sharp corners than i t i s when on!ly a-c or impulse voltages are applied. I n measuring d-c voltages with sphere and rod gaps, the present a-c crest voltage standards and the present a-'c voltage atmos- pheric correction factors may be used to w i t h i n an'acctiracy t y p i c a l of such gap measurements i f the t e s t gaps are made to spark over w i t h i n 5 seconds a f t e r the application of voltage. 2. Reference 1, Page 18, reports dual values f o r longer gaps for impulse voltages, but not f o r a-c voltages. POLYELECTROLYTES R. M. Fuoss Ste r l i n g Laboratory Yale University New Haven, Conn. Progress along two l i n e s of research was reported. F i r s t , v i s c o s i t i e s of synthetic polyelectrolytes (obtained by adding butyl bromide to poly^/inyl- pyridine) were measured i n a series of mixtures of nitroraethane and dioxane, covering the range of iÌ O to 16 i n d i e l e c t r i c constant. I t was found that the r a t i o of specific v i s c o s i t y to concentration increased with d i l u t i o n , i n a way similar to the behavior of the same electro l y t e i n aqueous solutions. Furthermore, the addition of a simple one-one el e c t r o l y t e (tetrabutvlammonium bromide) to these solutions decreased the v i s c o s i t y r a t i o at a given concentration, again paraJlelling the observations on aqueous solutions. The increase i n reduced visco s i t y with d i l u t i o n i s assumed to be a consequence of decreased association of the small counter ions with the large polycations on d i l u t i o n ; the r e s u l t i n g increased i n t r a - molecular repulsion between unpaired positive charges causes the polymer chain to expand, and thereby increases the hydrodynamic i n t e r a c t i o n which produces the v i s c o s i t y r i s e . The experimentaD results i n a l l solvents studied so f a r can be summarized by the empirical formula z = D + A/ (1 + B 74) where z i s reduced visco s i t y (specific v i s c o s i t y over concentration), c i s concen- t r a t i o n , A and D are constants which depend on the molecular weight of the poly- e l e c t r o l y t e and B i s a constant which depends on the d i e l e c t r i c constant of the solvent.
