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.
and in the case of seven determinations the percentage deviation of the mean ±0.62%. Although the percentage of the average deviation from the mean as shown in Table 2 is less than 0.62%, this value was accepted as the percentage deviation of the mean in the water equivalent. The accepted value of the water equivalent was taken as 961 (±6) gram-calories.
Specific Heat Determination
The water equivalent of the calorimeter having been determined, it is now possible to measure the quantity of heat carried into the system by any material introduced into the calorimeter at a temperature higher than the calorimetric system. If the mass of the material and its specific heat be known, it is possible to compute the temperature to which this material was introduced. It should be remembered that our aim has been to determine the temperature at which the film leaves the projector. It is obvious, therefore, that the specific heat of the film must be known before we can by this calorimetric method obtain the desired results. It is possible to determine the mass of film introduced and by means of the calorimeter to measure the total heat carried into the system by a given mass of film. But it is impossible from these data to compute the temperature of the film introduced unless its specific heat be known. The next step in the work was therefore a precise determination of the specific heat of motion picture film. Since motion picture positives vary enormously in average density and hence in the amount of metallic silver present, the specific heat of any particular motion picture positive will depend to a certain extent upon its average density. Computations based upon the specific heat of silver and the mass of silver required to give a specified optical density indicated that this variation in specific heat of positives of different average density would be relatively small. It was thought worth while, however, to measure the magnitude of this factor directly. Motion picture film is made by coating the positive emulsion upon a transparent support. Two different types of support are used for this purpose, these being designated for convenience as cellulose nitrate and cellulose acetate. Since these supports are of different composition, it is to be expected that the specific heat will be somewhat different in the two cases. It was therefore deemed advisable to make specific heat measurements on each type of motion picture film.
A photograph of the calorimeter set up to measure the specific heat of film is shown in Fig. 5. The two snap switches situated on the front side of the calorimeter control the fan motor and the film intake sprocket motor which rests upon the left top corner. The wooden box that rests on the farther right corner and in which is a roll of film served as a thermal insulator. The film was placed in this box and both were put in an electrically heated oven the temperature of which was maintained constant. After being allowed to remain for a time sufficient to insure the attainment of temperature equilibrium between oven and film, the box was taken from the
96