Observation of Aqueous Dye Dispersions at High Temperature I ‐ Construction of a Simple Microscope Pressure Hot Stage

There is at present, considerable interest in the behaviour of aqueous dye dispersions at high dyeing temperatures and in the variable solution properties of such dispersions prepared from metastable and stable dye solids. Earlier methods to observe dyebath conditions include the Microdyeoscope designed by Millson 1. This required a large dyebath, the solution from which passed through a cell situated in the focal plane of a microscope. The fibre or filament to be dyed was held in the cell. Observation was limited to temperatures of less than 100C. A cell formed within the dyebath by two inverted periscopes facing each other at a fixed distance has also been described 2 which allows the rate of dye concentration change to be determined spectrometrically. More recently Biedermann 3 has used a ‘microautoclave’ in which a composite (Teflon/glass) optical cell enclosed in a metal holder and heated indirectly on a Reichert microscope hot‐stage was used for examining crystal growth and habit changes in dye dispersions up to 140C. This autoclave was, however, clumsy to use, the heat transfer to the liquid was poor, and the cell could not easily be scanned. Also the material was not in the normal focal plane of the microscope. In the design described in this paper we have eliminated several of these disadvantages to provide a cell which is more easily scanned and incorporates a combined heating and direct temperature reading control unit.