We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
250 J. M. CALHOUN Vol 43, No. 4
This means that the values reported in this paper for the humidity coefficient of linear expansion of film are too small by about 0.005 per cent of the dimension per 10 per cent RH. Permanent shrinkage was determined by making the initial and final measurements at the same conditions of relative humidity and temperature, generally 50 per cent RH at 70 F.
Temporary Expansion and Contraction. — Photographic film expands when heated and contracts when cooled at constant relative humidity. The thermal coefficient of linear expansion of most films is approximately 5 X 10~5 in. per in. per degree F (0.05 per cent per 10 F) at normal temperatures. However, in practice when the temperature increases the relative humidity generally drops, and since moisture has a greater effect than heat, the net result may be a contraction rather than an expansion.
The humidity expansion or contraction of film is much more important than purely thermal expansion from a practical point of view.' When the film base takes up moisture it swells, and when it loses moisture it contracts. The magnitude of this effect is greater with emulsion coated film than with uncoated base because the emulsion has a greater tendency to contract than the base as the relative humidity is lowered (cf. Table 5). The base is compressed slightly by the emulsion under these conditions, thus increasing the contraction of the film at low relative humidities. The humidity expansion or contraction of film follows the change in moisture content, so that the dimensions at any given instant vary with the relative humidity of the atmosphere and the rate of conditioning of the film.
The magnitude of the humidity coefficient of linear expansion of common motion picture films varies from 0.04 per cent to 0.12 per cent of the dimension per 10 per cent change in relative humidity at 70 F. The change in dimension with change in equilibrium relative humidity is very nearly linear between 20 per cent and 70 per cent RH, but is somewhat greater below 20 per cent and above 70 per cent RH. As already mentioned, hysteresis plays a part in humidity dimensional changes, the film being slightly shorter if equilibrium at a given relative humidity is approached from below than if it is approached from above (cf. Fig. 5).
The thermal expansion and humidity expansion of photographic films manufactured in the manner we have described, are generally from 10 per cent to 40 per cent greater in the width wise direction than in the lengthwise direction. This is caused by the partial orien