QUI
358
QUO
similar kind. All of which substances are found objection-able, in some respect or other, for this use, sand being theonly perfectly suitable material that can be easily met with ;on which account, it has been always justly preferred. Purefirm crystallized sand is the best; though all pure sands arenot equally proper for this purpose.
It is stated by Sir Humphry Davy, in his work on Agri-cultural Chemistry , that there are two modes in which limeacts as a cement ; in its combination with water, and in itscombination with carbonic acid. When quick-lime is rapidlymade into a paste with water, it soon loses its softness, andthe water and the lime form together a solid coherent mass,which consists of seventeen parts of water, to fifty-fiveparts of lime. When this hydrate of lime, while it is con-solidating, is mixed with red oxyde of iron, alumina, or silica,the mixture becomes harder and more coherent than whenlime alone is used ; and it appears, that this is owing to acertain degree of chemical attraction between hydrate of limeand these bodies ; and they render it less liable to decomposeby the action of the carbonic acid in the air, and less solublein water. It is thought that the basis of all cements that areused for works which are to be covered with water must beformed from hydrate of lime ; and that the lime made fromimpure lime-stones answers this purpose very well. Puzzo-lana, it is said, is composed principally of silica, alumina, andoxyde of iron; and it is used mixed with lime, to form cementsintended to be employed under water. It is stated that Mr.Smeaton, in the construction of the Eddystone lighthouse ,used a cement composed of equal parts, by weight, of slakedlime and puzzolana. Puzzolana , it is said, is a decomposedlava . Tarras, which was formerly imported in considerablequantities from Holland, is found to be a mere decomposedbasalt : two parts of slaked lime and one part of tarras formthe principal part of the mortar used in the great dykes ofHolland. It is supposed that substances which will answerall the ends of puzzolana and tarras, are abundant in theBritish islands. An excellent red tarras may be procured inany quantities from the Giant’s Causeway, in the north ofIreland : and decomposing basalt is abundant in manyparts of Scotland , and in the north of England where coalis found.
ntS u
It i3 observed that Parker’s cement, and ce ®® 0 uS>same kind, are mixtures of calcined ferruginous, sialuminous matter, with hydrate of lime.
It is noticed, that the cements which act by
with carbonic acid, or the common mortars, ° r ® or tar9mixing together slaked lime and sand. These ^first solidify as hydrates, and are slowly converted. 1
nate of lime by the action of the carbonic acid °‘ . jjjn<h ,was found by Mr. Tennant, that a mortar of 4111 er 'three years and a quarter, had regained sixty-thre® tl^of the quantity of carbonic acid gas, which c ° n ® f( j n e39 ^definite proportion in carbonate of lime. The dep etl [the mortar in very old buildings is also thought . ona te®upon the perfect conversion of all its parts into ca ^ . g s9 i >lime. The purest lime-stones are the best adapte > _ gto ofor making this kind of mortar. The magnesiani g e nej|'make excellent water-cements, but act with too 1 _ V 1
upon carbonic acid gas, to make good common m y®“.Romans, on Pliny ’s authority, made their best 1110 jjj n e<l "'jbefore it was used; so that it was partially c °® gU pp° se ’carbonic acid gas before it was employed, it 1 I# ’See more on this subject under the articles OEMortak, and Plastering .
niao e
taken out
reg U!
1st
ofany— ar e,
ground-plat, or floor. Thus, if the ground-pl at ^ke 9or oblong, and a piece be taken out of a corner,court, or yard, &c., the piece is called a quirk. n &° a .
Quirk-Mouldings are the convex parts of Gr re . e nt ri ‘ings, where they recede at the top, and for® a c0 ver3 1angle with the soffit, or level surface wbicmoulding. ro i-re ver ?T
Quirks, in moulding, belong to the ovolo and se ’
QUOIN, or Coin, (from the French , coin, ° ^
cuneus ), a wedge. See Coin . , cor ner9 t M
Quoins, (from the French coin, a corner), j uge( ] for ,brick or stone walls. The word is P articl ^h«i thes estones in the corners of brick buildings. j janl fers“out beyond the brick-work (their edges being cthey are called rustic quoins.
K.
RAF
RABBET, or Rebate, see Rebate.
Rabbet-Plane, see Plane.
RABBETING, or Rebating, the planing or cutting ofchannels, or grooves, in hoards.
RACK, the case in a stable where the hay is placed forthe horses.
RADIUS, in a circle, the right line drawn from the centreto the circumference.
RAFTERS, (Dutch), pieces of timber, which, standing bypairs on the reason-piece or raising-piece, meet in an angle atthe top, and form the roof of a building.
It is a rule in architecture, that rafters should not standfarther than twelve inches asunder.
For the sizes or scantlings of rafters, it is advisablethat principal rafters from 12 feet 6 inches, to 14 feet6 inches long, be 5 inches broad at the top, 8 inchesat the bottom, and 6 inches thick. Those from 14 feet6 inches, to 18 feet 6 inches long, to be 9 inches broad
R A I
ul the foot 7 ■ i
those from’18 tbe to P> and 7 inches thick. ~ jQ
inches broad at thf e ches > to 21 fe et 6 inches, to be
*!<*• Single raFt/° 0t A » inehes ‘he top, and 8
inches ia their sm ^ ^ ee£ ® inches long, must be
■Raptejjo square. * $
F 0 °f> 80 that their timbers disposed in the 9 }^ ore r
mg which is surm ^may be in planes parallel to ther °of; but VoTo ^ *>7 them. See the article Boor,RAG-STON/Tt'^y Mechanical Carpe^W°f late, see Quarry o£ ' limestone much used m
applied varied,?. , the German > riegel), in archil
which ]i e honv/7 ,f articu)a rly to those pieces of gf) d
oy er and under tlf* ^ between the panels of m ’ nS t those6r the m. The word is also applied to
1 -nWer balusters jja
and un^
pieces of timber which lie overnies, staircases, &c. Also, to the pieces oihorizontally from post to post in fences, ' V1 ”
tb o'
at.