The foreign papers, French and German, are different from the English. They are porous and sized with starch, the English being sized with gelatinous animal matter. In all cases there is a difference in smoothness between the two sides of the paper, which may be detected by holding each sheet in such a manner that the light strikes it at an angle; the wrong side is that on which dark wavy bands, of an inch to an inch and a half in breadth, are seen, caused by the strips of felt on which the paper was dried. With most qualities of paper no difficulty whatever will be experienced in detecting the broad and regular bands above referred to; but when they cannot be seen, the wrong side of the sheet may be known by wire markings crossing each other, or if the paper be wetted at the corner, one side may appear evidently smoother than the other. PREPARATION OF SENSITIVE PAPER. There are three principal varieties of sensitive paper in common use, viz. the Albuminized, the plain, and the Ammonio-Nitrate paper. Formula I. _Preparation of Albuminized Paper._--This includes the salting and albuminizing, and the sensitizing with Nitrate of Silver. _The Salting and Albuminizing._--Take of Chloride of Ammonium, or Pure Chloride of Sodium 200 grains. Water 10 fluid ounces. Albumen 10 fluid ounces. If distilled water cannot be procured, rain water or even common spring water[40] will answer the purpose. To obtain the Albumen, use new-laid eggs, and be careful that in opening the shell the yolk is not broken; each egg will yield about one fluid ounce of Albumen. [40] If the water contained much Sulphate of Lime, it is likely that the sensitiveness of the paper would be impaired (?). When the ingredients are mixed, take a bundle of quills or a fork, and beat the whole into a perfect froth. As the froth forms, it is to be skimmed off and placed in a flat dish to subside. The success of the operation depends entirely upon the manner in which this part of the process is conducted;--if the Albumen be not thoroughly beaten, flakes of animal membrane will be left in the liquid, and will cause streaks upon the paper. When the froth has partially subsided, transfer it to a tall and narrow jar, and allow to stand for several hours, that the membranous shreds may settle to the bottom. Then pour off the upper clear portion, which is fit for use. Albuminous liquids are too glutinous to run well through a paper filter, and are better cleared by subsidence. A more simple plan than the above, and one equally efficacious, is to fill a bottle to about three parts with the salted mixture of Albumen and water, and to shake it well for ten minutes or a quarter of an hour until it loses its glutinosity and can be poured out smoothly from the neck of the bottle. It is then to be transferred to an open jar, and allowed to settle as before.