title: Permanent turbidity standards.
abstract: Permanent turbidity reference standards suitable for measurement of microbial suspensions were prepared by suspending finely divided titanium dioxide in aryl sulfonamide-formaldehyde or methylstyrene resins. Turbidities of these standards, adjusted to a useful range for microbiological and immunological studies, were compared with other reference standards in use today. Tube holders for a Coleman Photonephelometer and a Nepho-Colorimeter were modified to eliminate the water well and to allow use of optically standardized 10-, 16-, or 18-mm test tubes. The standards and the tube holders have been used satisfactorily for more than 12 years.
mesh_terms: D000486:Allergy and Immunology; D008722:Methods; D008829:Microbiology; D010783:Photometry / Q000295:instrumentation*; D013535:Suspensions / Q000592:standards*
chemical_list: D013535:Suspensions