Filter paper

“ Ernest T. Selig, Lawrence, Kan., wishes to exchange photographs of the collection of animals in the Kansas State University for pictures of the government buildings at Washington, D. C. A part of the collection mentioned was in the Kansas building at the World's Fair.
Sir Knight John N. Prothero asks how to filter solutions. Take a piece of filtering-paper, which may be bought either at the druggist's or of the dealer in photographic goods, fold it through the centre (it comes cut in circles) , then fold it back and forth from the centre like a fan. ”

“ Prepare filter by adding 0.5 mL 0.26 N sulfuric acid to glass fiber filter on a glass tray. Heat for 1 hour at 100 °C. Load the filter, backed by a paper O-ring, into a cassette and seal with shrink band to enable open-face sampling. 2. Personal sampling pump, 1 to 2 L/min, with flexible tubing. ”

“ Filters of paper, when unsatisfactory, can be replaced by Gibbs's sand filter, Munroe's clay filter, and Carmichael's siphon filter. The chemist with recent years has added two metals to the list from which his vessels are drawn—nickel and aluminum. In the cheap and ready supply of reagents, which a few years ago were troublesome to make and costly of purchase, industry has done an important service to research ”

“ Our engravings are from The Engineer. A filter press consists of a number of narrow cells of cast iron, shown in Figs. 3 and 4, held together in a suitable frame, the interior frames being provided with drainage surfaces communicating with outlets at the bottom, and covered with a filtering medium, which is generally cloth or paper. ”

“ When paper filters are of large dimensions, or employed for aqueous fluids that rapidly soften the texture of the paper, or for collecting heavy powders, or metallic precipitates, it is usual to support them on linen or calico, to prevent them breaking. ”

“ A photographic printing frame with a black disc on plain glass is a convenient method of testing, and if, after forty-eight hours in summer, and a proportionately longer period at other times, the difference between the exposed and protected areas is marked, the paper must not be used where a permanent colour is required. Some tints will bleach completely with the treatment, and should be avoided as stock lines. To test water-fastness a piece of paper is left in warm water, or placed in cold water and heated slowly. If the colour is soluble it will very soon tint the water. ”

“ In various coated papers sheets with uneven coating or surface markings should not be included as "good" paper. A paper which is even in texture cannot be considered matched by a supply which is "wild" or cloudy in the look-through. Although wildness is sometimes accompanied by strength in paper, this is not always so, and it is desirable that printing papers should not be wild.
To analyse papers in order to discover chemical residues and to identify them requires some very delicate tests, and unless one has had an extensive chemical training, mistaken conclusions may result. ”

“ As a rule, however, it is preferable to use only one drop of a reagent, and to follow closely under a low power of the microscope, its action, both upon the material of paper and upon the ink of any writing, which it may render visible.
The detection of mechanical erasure, which as was mentioned above, is frequently indicated by the paper being thinner and more transparent at that place, is often rendered more certain by photography. ”

“ Such distortion—for a distortion it really is—may frequently be turned to good account, and under certain conditions it may prove to be a help rather than a hindrance. Some slight inaccuracy in the fitting of any part of the design may occasionally be corrected by inserting patches of thin paper under the cylinder covering, so as to almost imperceptibly increase the pressure over the required area. This idea in its application to “making ready” at a tin-printing machine will suggest many possibilities to the resourceful printer, and if intelligently treated will rarely prove troublesome. ”

“ Creasing from defects of the machine, make-ready, or printing surface must not be visited upon the papermaker. If the paper will not respond to exposure to air, feeding the narrow way of the sheet may overcome the difficulty, or, if the size of the machine permits it, cutting the paper in half and rearranging the forme or other printing surface and putting on an extra feeder.
Art and other coated papers which have the coating fixed to the paper with glue in addition to the liability to wavy edges, may be troublesome by reason of the surface lifting or picking. ”

“ Every printer knows something of the effect produced by excess of water upon printing inks. It hardens and stiffens them by accelerating oxidisation. In course of time their free working on the rollers is interfered with, and loss of power is by no means the worst result. Weak and impoverished impressions, abnormal wear and tear of the printing forme, and excessive saturation of the paper may follow.
In lithography generally, and in lithographic machine printing particularly, the damping of the stone is a matter which requires constant and careful attention ”

“ Photographs are valuable in themselves, and the negatives serve for subsequent enlargements. They are unquestionably accurate, and the labour of making them being mechanical, may be delegated. If the print be in printer’s ink on white paper, the process is straightforward, first of obtaining a negative and afterwards photo-prints from it. The importance of the paper or card used to receive the finger print being quite white, has already been pointed out. An imprint on white crockery-ware is beautifully clear. Some of the photographs may be advantageously printed by the ferro-prussiate process. ”

“ A filter is an apparatus for separating from fluids the foreign substances mechanically intermixed with them and held in suspension. While this is all that most filters aim to accomplish, yet experiments show that a filtering material may be used which very markedly diminishes the foreign bodies usually held in solution in water, and also removes those held in suspension. ”

“ Papers which are loose in texture are usually soft-sized, and thus, having comparatively little size to hold the fibres together, will give off fluff or dust, consisting of small fibres, as soon as the paper is subjected to friction, even of the lightest description. Such paper in its passage through the printing machine gradually deposits its fibrous dust upon the printing surface, the rollers take it from there to the ink distributing surface, and the whole of the inking and printing becomes foul. ”

“ But, let us say in parenthesis, that while we deprecate the lack of artistic culture that prevents our printers from turning out artistic work, we do not for a moment claim that that which is not artistic is poor, or that all printing that is not rough is not artistic. The half-tone and coated paper have their use. If, as a matter of news or information, exactness is required, any sensible printer will turn to the half-tone for assistance. ”

“ From the foregoing list and descriptions it can be seen that papermakers have a variety of fibres at their command, and it is by selecting, sometimes by blending, fibres of different characteristics, that the manufacture of the large variety of papers is possible. Some of the demands made by the world of paper users are for papers which are very strong or very soft, absorbent, resistant to grease or water, very light, very dense, and the selection of the fibres and their treatment call for special knowledge and skill on the part of the papermaker. ”

“ A correspondent of Camera Craft makes proofs from his developed, but unfixed, negatives, by squeezing a sheet of wet bromide paper into contact with the wet film and giving an exposure several times longer than would be required under ordinary conditions, using the paper dry. If the developer is well rinsed out of the film, the exposure to artificial light necessary to make a print will have no injurious effect upon the negative, which is, of course, later fixed and washed as usual. ”

“ These machines are well suited for printing aerial negatives, either plate or cut film, if used where a source of electric current is available. The chief defect, which may be caused by faulty construction, is imperfect contact between paper and negative, a cause of serious unsharpness on prints destined for minute study in interpretation. ”

“ China clay, having no cohesion, does not assist in felting the paper in any way, but tends to weaken its resistance to wear. That weakness or tenderness is one feature of imitation art papers. After leaving the paper machine the paper is super-calendered, receiving a water finish, that is, the paper is just wetted on the surface immediately before entering the rolls of the calender. The loading is thus brought to the surface, and a very smooth level sheet is produced, only a little inferior, as a printing surface, to art paper. ”

“ Every little fault or attempt at touching up will be brought into prominence, and in cases where writing has been removed by the use of chemical reagents the slight yellow stain which is frequently formed upon the paper—a stain so trifling that it would not ordinarily attract notice—will appear as a dark blotch upon a photographic reproduction. It has frequently been claimed that it is possible to distinguish between different kinds of ink by means of photography. ”

“ To prepare by floating, pour the solution in a shallow tray, which needs not to be more than 20×34 inches, 30 inches being the width of the drawing paper usually employed; then roll the paper and place it on the solution. Now, taking hold of it by two corners, draw it out slowly: the paper will unroll by itself. This operation can be done by diffused daylight, but, of course, the paper should be dried in a dark room. It dries rapidly. Endless rolls are prepared by machinery. To expose, the drawing is placed in the printing frame, face downwards, and the sensitive paper laid over it. ”

“ Printers, or others, who accumulate large quantities of waste papers, will find that it pays to keep the various grades in separate receptacles, as a better price may be obtained for it in this way. Furthermore, by means of a baling press, the papers may be set aside in compact bales, which occupy less room and are not so great a fire risk as loose accumulations. The fact that 21.4 per cent of the paper-making fibers, according to United States Census Report, 1909, are derived from waste papers, indicates their importance as raw materials, while their use lessens the drain upon our forests. ”

“ For ordinary use, common book or print papers are employed, but these are usually given extra care and attention in the course of their manufacture; the stock is so manipulated as to not only secure the desired quality and finish, but also to counteract the tendency of the paper to stretch, which if not overcome is apt to destroy the register and injuriously affect the quality of the work. The better grades of lithographing-paper are made by applying a clay coating especially prepared to bring about the desired results. ”

“ Great pressure is in no case advantageous.
The filters already noticed are those that act by the fluid descending through the media; but in some cases the reverse method is employed, and the liquid filters upwards, instead of downwards. These are called ascending filters, and are often preferable to those on the descending principle, because the suspended matters that require removal by filtration usually sink, and thus a portion escapes being forced into the pores of the filter. They are also more convenient when pressure is employed. ”

“ Mineral fillers should not be regarded as adulterants. They are used, not as a means for adding weight, but for the sake of certain effects which are requisite in many papers. No filler is used on good writings or ledgers, as the printing requirements do not call for a closely filled surface or a mellow texture.
39 In book papers a varying percentage of clay is used, as it improves the printing quality by filling up the interstices between the fibers and increases opacity. Papers for half-tone printing require more filling, in order to have smooth, level surfaces. ”

“ From the sand settlers the stock runs on to a screen, through which it is drawn by means of suction. This process prevents fibres which are lumpy and too long from getting on to the machine, and allows only those of a certain size and length to go forward to be made into paper. An endless and very fine wire cloth, which is continually moving at the same rate of speed as the rest of the paper machine, takes the stock after it has been screened. This is the first step toward making the material into actual paper. Thick rubber straps on each side of the wire determine the width of the paper. ”

“ In cold weather it should be left longer, as it requires more time for the composition to absorb the ink. Remove the original carefully, and a reversed impression will be observed on the pad. To take off copies lay dry sheets of paper on the reversed impression, press gently, and remove quickly.
When you have taken all the copies you require wash the ink from the surface at once with a sponge and plenty of lukewarm water; never use hot water. The surface of the composition will allow considerable rubbing without fear of tearing it, if not done roughly and carelessly. ”