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stationary knife, fixed on the table over which To bring paper testing to the position which the paper travels.
it should occupy in order to be of real value to Water-marked papers have to be cut very the industry, it must be conducted on lines accurately at equal distances between the similar to those adopted by the Prussian water.marks; cutters with special clamps grip authorities. ping the paper and bringing a certain length Proper paper standards should be estabof paper forward to the cutting knives each lished; these have proved a boon, not only to time, are used for this purpose.
the buyer, but also to the paper-maker. The The “Guillotine" cutter is one type of results of all the tests, as well as of investigacutter, which is used for trimming sheets or tions into the composition of foreign papers dividing large sheets into smaller ones. The which compete against the home industry in essential part of this cutter consists of a heavy our markets, ought to be published periodically knife which, in its diagonal downward move. and thus placed at the disposal of our ment, cuts through the pile of sheets firmly manufacturers. pressed together on the cutting table.
In many instances, conclusions may be The importance of testing papers systematic. deduced from the results of these tests which ally has been recognised in various countries, but | might prove to be of value to the paper-maker. especially in Germany. The pioneer in this | Very often it will be found of importance to branch of testing was the splendidly equipped | ascertain microscopically the kind or kinds of testing Institute at Charlottenburg : this estab.
fibres from which a paper has been made. lishment includes a department devoted entirely For the microscopical examination of papers to paper testing, with the development of which are required a good microscope and various the name of its Director, Prof. Herzberg, is chemical reagents by means of which the intimately connected. The great value of fibres are coloured. To prepare a paper for paper testing does not consist alone in ascer examination, it is necessary to disintegrate it taining the quality and the properties of a by boiling small pieces, taken from various given sample ; the result of systematic tests parts of the sheet, for ten to fifteen minutes in cannot fail to be invaluable to the paper a weak solution of caustic soda (about i per maker, because, by their consideration, irregu. cent.); during this operation papers containlarities will be exposed and remedies will ing mechanical wood are coloured yellow. The suggest themselves.
boiled paper is now placed on a fine sieve, The real object of the testing institute was washed free from soda, and transferred to a not at first recognised by the German paper.
bottle containing garnets. After a short makers. The idea prevailed that such con
shaking with water, the pulp is drained and is ditions would be exacted as would only subject then ready for the preparation of the slides. the manufacturer to further heavy burdens. The chemical reagents used for facilitating Experience has proved, however, that the the investigation are potassium iodide iodine testing institute is a true and valuable friend solution, and zinc chloride iodine solution. On to the paper-maker. The preface of Herzberg's | placing a few drops of the former on a small -second edition of “ Paper Testing” (Papier quantity of the pulp placed on a slide, the
Prüfung), contains a letter addressed by the principal fibres show the following colour-German Paper-makers' Association, in 1900, ing :-Linen, cotton and hemp—light to dark to the Ministry of Education, which expresses brown. Straw and jute cellulose-grey. Wood the prevailing opinion so clearly, that I think cellulose and esparto-partly grey, partly it will be of interest to give a translation of it
brown. Manila hemp-partly grey, partly here :
brown, partly yellowish brown. Wood pulp
(mechanical) and raw jute-partly yellow, “The work of the Charlottenburg Institute since
partly yellowish brown. its foundation, has been followed by the German paper-makers with the greatest interest. Although
Zinc chloride solution gives the following reat first it was not considered always convenient to
actions :-Cotton, linen, and hempclaret red. have the department of paper testing, which was
Wood, straw, esparto, and jute celluloseestablished simultaneously with the institute, as a
partly blue, partly reddish and blueish violet. severe judge, no attempt has been made to conceal
Manila hemp-blue, blueish violet, dull yellow, that paper testing has been a powerful factor in con. I and greenish yellow. Wood pulp and raw tributing to the growth, the importance, and the jute-lemon to dark yellow. prosperity of the industry, and in establishing its fame! Before applying zinc chloride solution, the as against foreign countries."
| pulp must be freed from water by squeezing it
on a porous plate. The fibres have to be ments may be conveniently made to within separated with a pair of platinum preparing 1, 0·001 mm. needles and then covered with a thin cover Before proceeding with the testing of glass.
machine-made papers, the machine way and Considerable experience is required in work- | the cross way of the paper respectively must ing with the microscope and a careful study be ascertained. Both methods used are based of the structural characteristics of the different on the assumption that the fibres in the fibres is essential.
machine way are more closely felted than in Cotton fibres appear under the microscope the cross way. as flat ribbons, usually twisted upon them- Valuable conclusions may be drawn from selves. The flax fibre appears round and fairly the results of determination of the resistance regular, and shows a distinctly visible narrow which a paper offers to tearing. Papers which central canal. Numerous dark lines run cross | have to be tested should be kept for some time ways, and are due to pores in the fibres. The in a room the air in which contains a known so-called linen bulbs are very characteristic percentage of moisture, as the results are conwidenings of the fibre. Hemp fibres, as present siderably influenced by atmospheric conditions. in papers, cannot be distinguished with cer- | Strips, 15 mm. in width, are then cut length tainty from flax fibres. Mechanical wood shows ways and cross ways from different sheets. a ragged torn appearance and its structure is The chief tearing machines used in paper not a fibrous one. The pitted vessels or pores, tearing are those of Schopper, Hartig-Reuschwhich appear in the shape of two concentric Leuner, and Wendler. In Schopper's type, rings, are very plainly visible. Cross mark the strip of paper, 180 mm. in length, is susings on many of the wood cells may also be pended vertically between two clips, and by frequently noticed. The bast fibres of jute are | means of a simple hydraulic device, the load distinguished by a distinctly visible canal, the is gradually increased, until the strip breaks. width of which varies considerably. In some The breaking load and the elongation are places it is completely obliterated, and appears indicated on two scales. as a single line.
In the Hartig - Reusch - Leuner type of Wood cellulose fibres are usually flat, often machine, tension is put on the strip by twisted and not unlike cotton. In many in means of a steel spring, and the breaking stances the characteristic rings as seen in the load as well as the elongation are given in mechanical wood are plainly visible in the the form of a curve, the apparatus containcellulose.
ing an automatic registering device. Straw fibres are round and smooth and The Wendler tearing machine, in which the accompanied by numerous cuticular cells load is increased by means of a spring, differs some of which are very wide and flat whilst from the last named in that the breaking load others are peculiarly marked and serrated. and the elongation are indicated on separate The spiral shaped cells carry a ring at each scales. end and although the cells are mostly torn, The tensile strength of papers may be very the rings may be always found in straw papers. conveniently expressed by giving the length
Esparto fibres and cells are very similar in of a strip of paper which, if fastened at one end appearance to the straw fibres and cells. The and allowed to hang free, would break by characteristic small pear-shaped hairs or cells, its own weight. The width of the strip is which are always found in esparto papers, immaterial. afford, however, a ready means of distin The resistance which a paper offers to guishing esparto from straw.
crushing, rubbing, and folding, may be conTo ascertain the respective quantities of sidered as next in importance to its resistance fibres present in a paper it is necessary to to tearing. Although a paper may be quite compare the microscopic preparation with good so far as tearing is concerned, its refibré mixtures of known composition. Very sistance to rubbing, &c., may not necessa. considerable experience is, however, required rily be so satisfactory. Tests of this kind to obtain results possessing a high degree of have until lately been exclusively made by accuracy.
hand, a method the results of which obThe thickness of a paper may be ascer viously depend much upon the individual by tained by using one of the ordinary micro whom the tests are made. Schopper has meter arrangements, such as those of Schopper, constructed a special machine for this purRhese and others by means of which measure. | pose which has been found to give reliable
fibres which have been used in the manu- Rosin size in a paper may be readily defacture because the amount of natural ash of tected by boiling a small piece with glacial the fibres varies considerably. Thus white acetic acid and pouring the product into dislinen contains about 02 per cent. of ash, tilled water. The water will become opalescent whilst adansonia yields about 7 per cent. iif rosin size is present. The presence of starch
The quantity of ash in a paper is ascertained in a paper is ascertained by means of potasby incinerating a weighed piece of the paper sium iodide iodine solution, with which the in a skeleton cylinder made of strong platinum characteristic blue colouration is obtained. wire. The residue is weighed either on a l . An excellent reagent for animal or tub-size is Millon's reagent, i.e., mercuric nitrate. Tub. The presence of mechanical wood in papers sized papers, if moistened with this solution may be detected by the characteristic reaction and slightly warmed, 1urn pink or red.
with solutions of aniline sulphate (yellow). Papers which are used for special purposes, naphthylamine hydrochloride (orange), and as for instance, for the wrapping of polished phloroglucinol (magenta red). The quantity steel and other articles, should be carefully of mechanical wood can be ascertained with examined for free chlorine and for free acid. | a certain degree of accuracy, by comparing A quantity of the paper is extracted with boil. | the depth of colour produced with that given ing water and the extract tested for free by paper of known composition. chlorine with potassium iodide starch paper In many chemical industries, such for in.
and for acid with Congo red solution, a colour- stance, as those concerned with the manu. ing matter which turns black with free acids. facture of the simpler coal tar products, the
The ink and water resisting qualities of results of laboratory research can be imme. papers are tested by means of solutions of diately applied in the works itself. The ferric chloride and pure tannic acid, which, mechanical appliances used on the large when mixed, produce a black colour lake. The scale are, as a rule, of a quite simple ferric chloride solution is applied to one side, character and the carrying out of the prethe tannic acid to the other side of the paper. parations in the works is not complicated by Penetration and consequent contact of the the necessary use of highly intricate machinery. two solutions will be impossible if the paper is In the cases of other industries of a chemical hard sized, whilst the grey or black discolour character, such as bleaching, dyeing, calico ation will rapidly appear on soft sized papers. printing and finishing, the application of any