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The fundamental principles and methods of the sensitometry of photographic papers established by Jones, Nutting, and Mees in 1914 are reviewed. The necessity for the use of intensity scale exposure rather than the older time scale methods is shown.An account of the evolution of the design of an optical wedge sensitometer to fulfill the required sensitometric specifications leads to the description of a new instrument used in this study of the sensitometric characteristics of photographic papers. Details of the complete sensitometric process are given. The resultant characteristic curves from the different types and grades of papers are described and interpreted. The typical characteristic curve of modern papers is discussed and a revised method of determining numerical values, which describe the curve for practical purposes, is given. The new interpretation of the shape of the shoulder region of the curve is significant with respect to the quality of tone reproduction. The new group of characteristic values—speed, maximum gradient, exposure scale, maximum density, and contrast—is defined and discussed. Numerical values obtained by the new sensitometric method are given in tabular form for most of the current types and grades of photographic papers.

The results obtained in Section B may be summarized as follows: 1. (a) The brightness contrast in the object chosen as a “typical landscape” (Fig. 5) was found to be 39, the highest light having a brightness of 2500 millilamberts and the lowest 64 millilamberts. 2. (b) A panchromatic material was used in making the required negatives in order to minimize the distortion of the visual tone relations due to color effects. By developing a series of sensitometric strips the time of development required to give any desired gamma was determined. The curves obtained show that the exposure latitude of this material is 35, whjch is approximately sufficient for the rendition of the entire object on the straight line portion of the characteristic curve. 3. (c) A group of nine negatives was made, each having identical exposures, the development time being varied to give gamma values ranging from .38 to 1.32. The densitometric characteristics (D max., D min., and γ) of these negatives were determined by density measurements made directly thereon and by density measurements made on sensitometric strips developed with each negative. 4. (d) Using the negatives thus obtained groups of prints were made from the appropriate negatives on thirty-seven different developing-out papers selected to cover the entire range of contrast available in materials of this type. From the prints made on each developing-out paper judgement was made by seventy-five observers on the negative producing the optimal photographic quality. The data thus obtained have been examined critically, and from it certain conclusions have been drawn relating to the characteristics of the observers, the repeatability of judgments of print quality, and the average photographic quality considered as optimal by observers differing radically in their training for the judgment of print quality. li ](e) A summary of the statistical data thus obtained is given, from which is obtained the gamma of the optimal negative for each of the developing-out papers used. The probable error to be remarkably small and indicates that these values may be relied upon as truly indicative of the negative quality which will give the best possible print of the particular test-object used in this work on each of the positive materials. 5. (f) From density measurements made directly on the positives, values of maximum and minimum density for the optimal positive are derived, the difference between these giving the density scale for the optimal positives. These values relative to the optimal positives, together with the densitometric measurement relative to the optimal negatives, constitute the data from which, in connection with the sensitometric data to be obtained in the following section, values of contrast for the positive materials are computed.

The structural properties of paper as low-cost building material are investigated in a pilot study which gives the results of a limited number of tension, creep, and flexure tests. Certain problems encountered in all-paper construction are discussed, the significance of creep is considered, and a mode of failure peculiar to all-paper construction is observed. The structural integrity and flexibility of form available with paper are illustrated by the fabrication and testing of a cylindrical shell.

It is shown that water adsorbed by paper cannot be completely removed by pumping while immersed in an impregnating compound which wets the paper. A theory which explains this effect is presented, according to which the equilibrium moisture content of paper pumped under these conditions does not correspond to the external pressure but to one 2λ R greater than this where λ is the surface tension of the impregnant and R the effective pore radius. The application of these findings and the theory to the preparation of experimental samples of impregnated paper of controlled moisture content; to the determination of moisture in impregnated paper; to the drying and impregnation of paper and to the investigation of the pore structure of solids is discussed.

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A system of numerical specification of the sensitometric curves of photographic papers is described. Comparison of original curves and their reproductions, made by a new curve duplicator from specifications, shows that the system is satisfactory for production control.

1. 1. Several reducers commonly used for the reduction of negatives have been studied and modified in such a way as to be applicable to the reduction of p 2. 2. A classification has been made on the basis of the character of the modification in the characteristic curve obtained with several reducers. 3. 3. Observations have been made relative to the staining of the deposit and of the gelatine resulting from the action of the reducer and its reaction pr 4. 4. The character of the action of a given reducer on negatives cannot, in all cases, be taken as indicative of what its action on prints will be. 5. 5. Reducing solutions made up according to the formulae appended to this report have been found to give satisfactory action on printing-out papers, the modification which it is desired to make in the print.

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