No one, unless he is likely to be a large consumer and able to afford a proper apparatus, should attempt to make P.O.P. The paper is sold so cheaply that it could only be made in large quantities at the same price; and expensive plant and long experience are necessary to ensure good results. Prepare two solutions. (A) Ammonium chloride 50gr., Nelson's No. 1 gelatine 160gr., Heinrich's hard gelatine 300 gr., distilled water 20 oz. (B) Silver nitrate 150 gr., distilled water 1/2oz. Dissolve the gelatine in 1 oz. of water, warm and add the remainder; then add solution (B) a little at a time, stirring thoroughly between the additions. Allow the emulsion so formed to set, then wash by squeezing through mosquito netting, and washing or soaking in a few changes of distilled water. The shreds must then be well drained, melted down, and the emulsion is ready for use. The paper is unrolled over the surface of the emulsion, which is placed in a trough or a dish tilted to an angle.