Acid resistance development

Development of Resistance. One of the principal disadvantages of sulfonamide therapy is the emergence of dmg-resistant strains of bacteria. Resistance develops by several mechanisms overproduction of PABA (38) altered permeabiUty of the organisms to sulfonamides (39) and reduced affinity of dihydropteroate synthetase for sulfonamides while the affinity for PABA is retained (40). Sulfonamides also show cross-resistance to other sulfonamides but not to other antibacterials. In plasmodia, resistance may occur by means of a bypass mechanism in which the organisms can use preformed foHc acid (41). 

Acid resistance This can be checked by using N/IO (H2SO4) solution. When a few drops are spilt on the test piece, or when the test piece is dipped for almost half an hour in the solution. It should develop no corrosion spots on the surface. 

Newer fabrics, not in common use but in development, test, and field trials, are described for higher temperature applications by Reference [50]. Application to 400°F—2100°F are potentially available using ceramic fibers Nextel 312 , laminated membrane of expanded PTFE on a substrate, polyimid fiber P-84, Ryton polyphenylene sulfide, and woven fiberglass. The heat and acid resistance of these new materials... 

After 1950 some serious attempts were made to improve dental silicate cement. Notable were those of Manly et al. (1951) and Rockett (1968) also, Pendry reported an acid-resistant cement containing indium (Pendry Cook, 1972 Pendry, 1973). None of these experimental materials went into production. These attempts came too late in view of progress made in other directions, and the picture of dental silicate cement remains one of an essentially traditional material which has changed little since the original developments made mainly by German chemists prior to 1914. 

PuraSiv N A process for removing nitrogen oxides from the tail gases from nitric acid plants, using an acid-resistant zeolite molecular sieve. Developed by the Union Carbide Corporation in 1971. Not to be confused with PuraSiv HR, Type N (see previous entry). 

The use of high-concentration gels and varnishes has been practised clinically for many years by dentists and dental hygienists [180]. When originally formulated, they were designed to be used in application procedures based on the concept that fluoride becomes incorporated into the crystalline phase of the enamel and leads to the development of a more acid-resistant form of apatite. They were not expected to make any difference to the levels of fluoride in saliva, or to influence the demineralisation/dissolution phase of the behaviour of tooth mineral. 

At the borderline between semisynthesis and patterned synthesis, versatile total syntheses may provide access to diversified bioactive structures. Classically, analogues of the active drug are sought that avoid the resistance developed by pathogens and show reduced side effects. In lucky cases, chemical simplification has afforded the wonder drug. This is the case of sodium valproate (2-propylvaleric acid sodium salt), which was synthesized in the fall of the XIX century and nearly a hundred years later became a leading drug in the treatment of epilepsy. 

Granodixing Process, developed by the American Chemical Paint Co, Waterbury, Conn for rust prevention of iron, steel, zinc or cadmium consists in immersing the material in a hot soln of acid zinc phosphate. This operation forms an acid resistant coating. The resulting material may be painted... 

A considerable advance in the practice of stabilizing lacquer nitrocellulose was made by the development of a continuous process of boiling under pressure in acid-resisting tubes, 100 mm dia., up to 1500 m long (Figs. 164 and 165), The tubes are warmed or cooled by means of outer jackets being heated throughout... 

Enamels used on cast iron and aluminum have traditionally been composed of SiO., B Oi. PjOs, and PbO. The lead oxide produces good surface quality, fusibility, and acid resistance when properly formulated with other oxides. More recently some non lead-bearing compositions have been developed for both cast-iron and aluminum metals. Glasses containing lead oxide are not recommended for food contact surfaces. 

A number of methods have been developed in the last forty years for the dimensional stabilization of wood (1, 2). Unfortunately none of these have proved to be economically successful on a large scale. One of the methods, involving the treatment with furfuryl alcohol (3) was shown by Goldstein ( , 5) to impart both alkali as well as acid resistance to wood, giving it a distinctive black color. This treatment is of renewed interest at the present time because furfuryl alcohol is made from the renewable resource, corn cobs, and can also be made from the hydrolizate of hardwood waste (6J. 

The valves supplied with these pumps showed an erratic behavior at low flow rates, mainly due to a too large diameter of the valve balls and poor design of the valve seats and valve chambers. New pumpheads and valves were therefore developed, manufactured and mounted on the pumps. The heads and fittings were made from PVDF with valve seats and 3 mm diameter balls in acid resistant steel. On these pumps the stroke length has to be set mechanically and this set-screw was modified so that it could be turned by a simple manipulator, if necessary. The electronic frequency control was modified for remote operation. 

---