Test specimen, hydrogen concentration

In these experiments we used a well-stirred continuous-flow reactor in which the test specimen was mounted. A sapphire window on the top of the reactor permitted the passage of infrared radiation to the thermal imager. The contents were mechanically stirred with an impeller whose shaft entered the reactor through a gas-tight seal. Hydrogen and oxygen entered the reactor at a rate controlled by electronic mass-flow controllers, and the exit stream was continuously analyzed for product concentration (water vapor in this case) which was recorded on a strip chart. 

Pancreatic amylase is more sensitive than malt amylase both in the sense that it loses its activity much more rapidly when held in aqueous dispersion, and that it is active only within a narrower range of hydrogen ion concentration. When the two amylases are tested in purified condition upon a dispersion of soluble starch at a temperature of 40°, and each in the presence of its optimum concentration of hydrogen ion and of chloride and phosphate, the enzymic activity of the amylase of the pancreas is fully twice that of the amylase of malt, fairly constant quantitative values being shown in numerous preparations of each enzyme made at different times and in several cases from different specimens of the original material. 

The current salt spray test, in which the plated specimen is exposed to a spray or fog of sodium chloride solution, is the most widely used accelerated corrosion test for coatings, and various procedures have acceptance tests in standard specifications in numerous countries. Over the years, the procedure has employed sodium chloride solutions of concentrations between 3 and 20 %, sometimes with the addition of hydrochloric acid or hydrogen peroxide. The salt spray test [ASTM B 117, Test Method of Salt Spray (Fog) Testing] has largely fallen into disrepute because of the recognition that its reproducibility and correlation with outdoor exj>osure were often poor. Cyclic salt spray testing as well as alternate electrolytes such as the "prohesion test solution have been found to produce more realistic results. 

---