CELTS 



1248 



CEMENT 



nor even in fairly-strong acids or alkalies. In 

 the che'mical laboratory paper is used for filter- 

 ing almost any liquid, and this filter paper 

 is pure cellulose. 



Very strong acids, however, act upon cellu- 

 lose. Parchment paper is made by dipping 

 paper into concentrated sulphuric acid for a 

 moment and then into water. The cellulose 

 swells on the surface and becomes hardened. 

 Strong alkalies also swell cellulose, a fact which 

 is made use of in making mercerized cotton. 

 A mixture of nitric and sulphuric acids con- 

 verts cellulose into the explosive nitro-cellu- 

 lose, known as pyroxylin or guncotton. Nitro- 

 cellulose is soluble in a mixture of ether and 

 alcohol, producing the compound collodion. 

 When collodion is used to dress wounds, the 

 alcohol and ether evaporate and a thin layer of 

 nitrocellulose is left which protects the wound 

 from infection. 



Artificial silk, or lustracellulose, is made by 

 dissolving cellulose in suitable solvents and 

 forcing the liquids through minute holes into 

 some medium which immediately reforms the 

 cellulose in fine threads which shine like silk. 

 In one process collodion is used. Here the 

 threads are formed by the evaporation of the 

 alcohol and ether. These threads are nitro- 

 cellulose at first, but this is then changed back 

 into cellulose by chemical treatment. In the 

 viscose process, the cellulose (usually wood 

 pulp) is swelled with the alkali and caustic soda, 

 and then treated with carbon disulphide. The 

 product, called viscose, is dissolved in a little 

 water and then is forced through the holes 

 into a strong salt solution. The threads formed 

 have only to be heated and washed to change 

 them back to cellulose. 



Cellulose is present in all foods of vegetable 

 origin. It is especially abundant in the stalks 

 and leaves of plants, and so we find a large 

 proportion of it in such foods as celery, lettuce 

 and spinach. Only a little of the cellulose is 

 digested by man (a much larger proportion by 

 herbivorous animals, such as the horse and 

 cow), but, nevertheless, it is practically indis- 

 pensable to the diet. It affords bulk and stim- 

 ulates the peristaltic (churning) motions of the 

 bowels. J.F.S. 



Related Subjects. Reference to the following 

 topics will be helpful : 



Carbohydrate Guncotton 



Cotton Protoplasm 



Explosives 



CELTS, sells, or kelts, or CELTIC PEOPLE, 

 a division of the Aryan branch of the human 



family, supposed to have been the first Aryan 

 settlers in Europe. The onslaughts of the 

 Teutons, Slavonians and other races drove 

 them westward, and at the beginning of the 

 historic period they were the principal inhab- 

 itants of Britain, Ireland, France, Belgium, 

 Switzerland and Northern Italy. About 235 

 B.C. a Celtic tribe conquered and settled that 

 portion of Asia Minor to which the name 

 Galatia was given. The Celts were a restless, 

 energetic people, and held their place in West- 

 ern Europe until conquered by the Romans, 

 who generally called them Gauls. Of the 

 Celtic peoples surviving at the present time, 

 there are two divisions, the Gaelic, or Gadhelic, 

 comprising the Scotch Highlanders, the Irish 

 and the Manx; and the Cymric, comprising 

 the Welsh and the Bretons (the people of 

 Brittany). The Cornish dialect, formerly be- 

 longing to the Cymric group, became extinct 

 only recently. 



CEMENT, sement' , or sem' ent. Pieces of 

 paper may be stuck together with mucilage 

 and paste, pieces of wood and other articles 

 may be joined with glue, and paper may be 

 fastened to walls with paste. We hold bricks 

 in a wall with mortar and fasten metallic 

 fixtures to glass lamps with plaster of Paris. 

 All preparations used for sticking articles to- 

 gether are known as cements. A cement must 

 be soft and pliable, so it will fill all spaces 

 and crevices where it is used. It must harden 

 or "set" within a reasonable time after it is 

 applied. Most cements are mixed with water, 

 and they harden on exposure to the air or 

 by a chemical change in the substance. Glue 

 and some other cements are softened by heat- 

 ing, and these harden on cooling. All cements 

 must have the property of adhering so firmly 

 to the objects to which they are applied that 

 on becoming solid they will hold them to- 

 gether. 



Portland Cement. The most important ce- 

 ment is that prepared from certain varieties 

 of limestone and used extensively for building 

 purposes. The varieties of this cement usually 

 recognized are natural rock cement, made di- 

 rect from a limestone containing a good pro- 

 portion of clay; Portland cement, and slag 

 cement. When the term cement is used with- 

 out qualification, Portland cement is meant. 

 This cement was first made in England and 

 took its name from its resemblance to a 

 limestone obtained from Portland, on the Eng- 

 lish Channel. There are two processes in the 

 manufacture, the wet and the dry. The cement 





