Show ITS 1 MANY USES an article written by an expert eldert at the smithsonian institution washington D C limb almie mortar has been used for so bolong long a time for plastering walls that it may be a source of surprise to wake up to the fact that another plastering material is being aged and has been used since its introduction into the field of nonmetallic non metallic building materials in about 1885 this material is the mineral gypsum the source of plaster of paris and cement plasters the annual sales of which now exceed those of lime plaster by many thousands of tons gypsum the crude substance from which these plasters and other various hard plasters are derived is a mineral similar in appearance to marble but much softer composed of sulphate of lime find and water it belongs to the lime containing group of minerals rals as does limestone but diners differs from the latter in that it is a sulphate while limestone isza isa carbonate its value as a building material is due to the fact that when a i perfectly dry piece is heated to an almost red heat a certain amount of water is driven off as steam leaving behind a white powder which has the power of taking up water I 1 gain again and becoming hard this asi powder is popularly known as plaster of paris in the division cf mineral technology in the U S national 1 museum at washington and es series of ex lu baity illustrates both the prop arties c of gypsum and the man processes process ss of commodities made from it and shows many of the finish finished cd products an especially constructed model IS 8 by 10 feet in size gives the visitor a fine idea of a gypsum plant in full s swing the buildings in s and machines are showie abow PJ on a scale 1 full size and ilac th c various processes involved in the manufacture of gypsum prod acts may be traced from start to finish all of the buildings are open section and illuminated to enable the student to observe the arrangement of the I 1 machinery and the methods employed despite its late introduction into the united states gypsum was known and used for years previously probably one of its earliest uses was to plas ter over the pyramid of choops built between and B C for remnants of this plaster are found to be almost identical with the best cement plaster t ar arnde ted ty the early writ in lips Ps 0 of aristotle pliny theo rh rastus arid others show that gypsum and its uses were known to them being soft white and it came to b be carved a rv into vases and other or ornaments and was also used in temple walls for the admission of light before th the e discovery of glass according to plaster of paris was first fir 11 aed ed to make plaster casts in about 33 B C this are disappeared pe qi ed P how however ever and was not re vi until 1 1480 A D when the method of casting in plaster was again used to obtain copies of ancient sculpture it is supposed that the phrase plaster of paris was first used about this time to designate the product obtained by heating gypsum and that it came about in this manner A shepherd while tending his flock in montmartre near paris made a fire in a hearth built of stones gathered from the field the heat from his fire some of the stones causing them to crumble into a fine white powder which was shortly wet by a storm and converted into plaster when the I 1 plaster dried and set it cemented the remaining stones into a solid hearth this new plaster or cement discovered by the paris shepherd came to be known as plaster of paris and has retained the name to this day the value of gypsum plaster soon spread to other countries and gypsum is now mined in france england germany switzerland italy sicily cana da newfoundland united states and some of the south american republics commercial gypsum is not an all ore in the same sense that gold silver and iron are ores but is a rock like sandstone occurring in beds or layers in the earth it is formed by deposition in water and has a worldwide world wide distribution I 1 trib ution the depth at which lberg are jcurd ehmes es the method of extraction one operation olie ration being similar to that by which all stone is secured nar namely riely quarrying and another similar to tile the mining of coal by the room and pillar process following its removal from the quarry or mine it is crushed and round ground then burned and finally mixed with various substances to make a ready mixed mortar many grades are made adapts bleto a variety of purposes and in some grades are added to keep the plaster from setting too rapidly by virtue of its being very little affected by heat and dampness s and the fact that it takes nes ness co color 0 r I 1 very wells well gypsum has many and varied commercial uses among the more important are the manufacture of partition tile plaster board wall plasters and to make molds for pottery and rubber stamps some miscellaneous uses are in dental and surgical work as a filler in paint and paper and for interior decorating and temporary structures like the buildings for large expositions such as the panama paci fie fic large large quantities of crude gypsum sll n are used in portland ce ment manufacture to retard the set for soil dressing commonly called land plaster as an adulterant in flour sugar and bak ing powder and in the manufacture of crayons blocks of clear I 1 white gypsum called alabaster I 1 are used by artists and sculptors 1 |