I 



APPENDIX 457 



Ordinary commercial papers usually consist of mixtures of the raw materials 

 tabulated above. Wood fiber papers may be made either from wood pulp obtained 

 by the action upon the wood of chemicals such as " bisulphite of lime " (sulphite 

 pulp) or caustic soda (soda pulp) or a mixture of caustic soda and sodium sulphate 

 (sulphate pulp) or by purely mechanical means such as holding blocks of wood 

 against rotating grindstones under water. Pulp produced by the former processes 

 are called " chemical wood " pulps, those by the latter " mechanical wood " or 

 " ground wood " pulps. 



QUALITATIVE EXAMINATION OF SIMPLE PAPERS. 



Place one of the small strips of paper upon an object slide and cover one end 

 with a large drop of water. After it has soaked for 10 or 15 minutes, carefully 

 scrape with the blade of a " spear point " dissecting needle. The scraping must 

 be done under water and the abraded material pushed to one side of the drop. 

 After sufficient material has been teased off, remove the strip of paper. Spread 

 out the pulp so as to have it evenly distributed and not too thick. Cover with a 

 cover glass and examine. Note well the morphological appearance of the entire 

 and ruptured cells. Make sketches in the note book. Examine with polarized 

 light. Remove the cover glass, dry the fibers and stain with iodine in potassium 

 iodide as directed below. Cover and examine. Remove the cover glass, remove 

 the excess reagent by means of filter paper, add a drop of sulphuric acid (sp. gr. 

 1.45), cover and examine again. Describe results obtained. 



Characteristics of Common Fibers. — The morphological characteristics of the 

 textile fibers have already been discussed above, those of wood, straw, esparto, etc., 

 cannot be adequately described without illustrations. 



Coniferous Woods. — Transparent, colorless, thin-walled cells with large central 

 canal. The most characteristic cells (tracheids) are long, narrow (or broad) very 

 thin-walled with either tapering or blunt ends, on their surface a longitudinal row 

 of faint but distinct circles with well-marked central pits or perforations. There 

 are also long cells, with tapering pointed ends and thickened side walls, usually 

 bent and twisted and therefore somewhat resembling cotton fibers but distinguish- 

 able from the latter by reason of diagonal or cross-hatched striations. A third 

 type of easily recognizable cells are broad, thin, with two or more rows of elliptical 

 pits or perforations. 



Non-coniferous or Broad Leaved Woods. — The elliptically pitted cells differ from 

 those of the conifers in a striking manner, they are larger, much broader, usually 

 have rounded or obliquely blunt ends and have many rows of pits, tiny depressions 

 and perforations. The long, slender, tough, tapering bast cells of the broad leaved 

 woods resemble very closely the vascular cells found in the conifers. 



Mechanical wood pulp under the microscope is distinguishable by its behavior 

 toward stains and its appearance. It consists of groups and masses of torn 

 more or less distorted cells. Chemical wood on the other hand consists largely 

 of free, detached entire cells. 



Esparto. — (a) Fine, slender, short, structureless, transparent cells with taper- 

 ing, pointed ends. 



(b) Very short cells with serrated sides. 



(c) Short, stubby hairs usually more or less comma-shaped. 



