Gelatin filters

The absorption spectrum of a dye shows not only an absorption maximum in the visible region of the spectrum but also an absorption minimum which indicates the wavelengths of radiation that are transmitted by the dye (Figure 2.18). Such dyes, in the form of stained glass or gelatin filters, provide the simplest approach to the design of monochromating systems. 

Gelatin filter sampler. The unit consists of a vacuum pump with an extension hose terminating in a filter holder that can be located remotely in the critical space. The filter consists of random fibers of gelatin capable of retaining airborne micro-organisms. After a specified exposure time, the filter is aseptically removed and dissolved in an appropriate diluent and then plated on an appropriate agar medium to establish its microbial content. 

Light separation by filters can be performed with coloured glass or dyed gelatine filters. The quality of separation and the thermal stability of the filters, however, have been improved considerably by the use of thin film interference systems, see [Id, 2, 6, 115]. 

Most Wratten Gelatin Filters are stocked in 2- or 3-inch squares. Stocks of 2- or 3-inch square filters cemented in glass are maintained only in filters usually used for general photographic work. 

A monochromator which isolates a narrow band of light. Glass or gelatin filters, interference filters, diffraction gratings or prisms can be used to isolate a narrow wavelength band of light. 

VUra-fiUrcUum through surfaces of standard porosity. The filters usually employed are collodion, cellophane and gelatin. From the strength of a gelatin filter the size of the pores may be calculated, and depend on the concentration of gelatin present, irrespective of the thickness of the filter. 

---