PLASTER OF PARIS 



4701 



PLATINUM 



demand considerable experience. Plastering 

 with cement is conducted in a similar manner 

 to lime plastering, but has to be done more 

 quickly, as cement dries and becomes unwork- 

 able much sooner. 



Estimating Costs. Ordinary plastering is 

 i for by the square yard, and in measuring 

 for it no deduction is made for window or door 

 *s (unless they are very large) nor for 

 ordinary baseboards. Thus the amount of 

 n a room fourteen feet long, twelve 

 wide and eight feet high would be com- 

 puted as follows: 

 Distance around room. In feet. 12 + 14 + 



'.4= 52 



Multiply by height. In fwt 8 



Area of walls, square feet 416 



ceiling. 12 ft.X!4 ft 168 



Total area to be covered, square feet 584 



Reduce to square yards (divide by 9> 64% 



Consult Rlchey's Building Mechanics Ready 

 Refer<n. Krkel's Cements, Limes and Plasters; 

 Miller's Plastering, Plain and Decorative. 



PLASTER OF PARIS. If gypsum is ground 

 and then baked to drive off the water, a fine 

 <lry powder, called plaster of Paris, is formed. 

 From mixing one part of this powder with two 

 parts water a thin paste results, which hardens 

 quickly on exposure to the air. This property 

 of plaster of Paris makes it valuable for casts 

 and for stuccowork, and it is extensively use.l 

 for both purposes. By adding a small quan- 

 tity of lime to the ; fry hard substance 

 resembling marble is produced. Under the 

 name of calcine plaster this mixture is often 

 used to cement lamps to their sockets and 

 for fastening fixtures in place where screws 

 bolts cannot be used. See GYPSUM; STUCCO. 

 PLATA, plah'tah, Rio DE LA, the estuary, or 

 funnel-shaped bay, formed by the Parana and 

 Uruguay rivers on the southeastern coast 

 of South America. A great volume of \\ 

 flows into it from these two rivers, creating a 

 powerful current, and there are many treacher- 

 ous shallows; navigation is therefore very dan- 

 is all along its extent of 200 miles. 

 far from the mouth, which is 143 miles wide, 

 u'ood, natural harbor of Montevideo, 

 Uruguay, while on ntinc side massive 

 docks are being built and deep channels are 

 dredged at Buenos Aires and La Plata. 



as discovered by Dias de Sol. 

 1516, but wa- to present name, which 



mean- > Sebastian Cabot. 



PLATEAU, platoh'. .\\ elevated plain 

 mountainous region by the uplift- 

 ing of great sections of horizontal strata PI .- 



teaus owe their formation to the same move- 

 ments that created the mountains. The distinc- 

 tion between a plateau and a plain (which see) 

 is chiefly one of altitude, the latter being gen- 

 erally not more than a thousand feet above 

 sea level. Plateaus are also more rugged, and, 

 because of their higher altitude, their streams 

 cut deeper valleys than do those of pi 

 These valleys may take the form of huge 

 gorges, such as the famous canyon in Arizona 

 (see GRAND CANYON OF THE COLORADO). Some- 

 times a plateau is so carved by Nature's sculp- 

 tors, wind and water, that it takes on the ap- 

 pearance of a range of mountains. This is true 

 of the Catskills in New York, for these beauti- 

 ful hills are really a part of the Alleghany pla- 

 teau (see CATSKILL MOUNTAINS). 



In North and South America the higher pla- 

 teaus are on the western side of the continents, 

 and the lower ones on the eastern side. A 

 plateau about a mile and a half high lies be- 

 tween the Rockies and the Sierra Nevadas in 

 North America, and one in Bolivia, South 

 America, is bordered by the giant peaks of the 

 Andes. The loftiest plateaus on the earth are 

 found in the Himalaya regions of Central Asia 

 "the roof of the world" (see PAMIR; TIBET). 

 In regions where there is little rainfall smaller 

 flat-topped areas are often found rising from 

 the main plateau. Such formations, called 

 mesas, are the work of erosion (see MESA; ERO- 

 >i"\ ). Economically, high plateaus are of little 

 value to mankind because their niggedness 

 makes commercial intercourse difficult or im- 

 possible, and climatic conditions are not favor- 

 able to the support of any considerable popula- 

 tion. Those of lower altitude are sometimes 

 excellent grazing grounds for sheep ami cattle. 

 Such areas are found in Western United States 

 and in the western part of Australia. The pla- 



of the Appalachian regions in Eastern 

 United States have valuable deposits of coal 

 and iron. 

 PLAT'INUM, the most valuable of all the 



lous metals, worth literally its weight in 

 gold. Its name, which is derived from tin 

 Spani>h word pint inn. the diminutive of plain. 

 meaning silver, was given to it by the Span- 

 iards because the ore which contains this metal 

 resemble- Phis ore, which was first dis- 



rcd in Peru about the middle of the eight- 

 eenth century, is called native platinum, and i- 

 usually found in beds of gold-bearing sands. 

 rs call it white gold. It occurs mostly 



nail, irregular grains, which contain 



metals, such as indium, osmium, rhodium. 



