416 



MECHANICAL. 



plaster of Paris, possesses the property of 

 swelling as it sets, it acts with considera- 

 ble force against the sides of the trenches 

 — forming a solid, compact mass as hard 

 as stone, and more firmly fixed in the 

 trench than the foundation could be if 

 built with any other material. 



In the lower course of footings to walls, 

 it is advantageous to have a great portion 

 of the stones — all, indeed, if the stone 

 will allow of it — running right through 

 the thickness of the wall ; at all events, 

 if these cannot be procured, it will be 

 proper to alternate the headers and 

 stretches, on both faces of the wall, so 

 that it may be well united in the direc- 

 tion of its thickness. 



Joints down the centre of a wall should, 

 as much as possible, be avoided. 



Rubble masonry is measured accord- 

 ing to custom, by the perch of 22 cubic 

 feet. 



Projections from the face of a wall of 

 12 inches, and under, are measured by 

 taking the face, and one return, for the 

 length. This multiplied by the height, 

 and this last quotient multiplied by the 

 thickness or projection will give the con- 

 tents in cubic feet, which, divided by 22, 

 will be the number of perches. 



Projections exceeding 12 inches meas- 

 ure as follows : Take the solid contents 

 of the blank space, and add the face, and 

 the return, or one foot, and proceed as 

 above to find the number of perches. 



This measurement is given for the 

 trouble of squaring and plumbing the 

 angles. 



Square isolated piers, 3 feet 6 inches by 

 3 feet 6 inches, and under, double meas- 

 urement. 



From 3 feet 6 inches up to 5 feet, one 

 and a half. 



From 5 feet up to 7 feet, one and one- 

 fourth. 



Over 7 feet, single or actual contents. 



No deductions are made for openings ; 

 but, if such openings exceed 6 feet in 

 width, the same to be deducted and the 

 jambs measured. 



For area steps, enclosed by walls, the 

 steps built in and set by the stone-mason, 

 measure the enclosing walls as walls, and 

 girt the steps and risers for the length of 

 sloping back, multiplied by the length of 

 the steps in the clear, and by one foot 6 

 inches for the thickness, will be the con- 



tents in cubic feet, and divide by 22 for 

 the number of perches. 



Circular work, double measurement. 



Range work is measured by the fool 

 superficial, and all openings deducted. 



Arches are charged at so much each. 



Note. — A perch of stone or masonry 

 is 16^ feet long, 1^ feet wide, and 1 

 foot high, or 24^ cubic feet. 



MEASTJEING BRICK.— Brick may be 

 used for nearly all the purposes to which 

 stone is applicable — for when carefullj 

 made, its strength, hardness and durabili- 

 ty are but little inferior to the more ordi- 

 nary kinds of building stone. It remains 

 unchanged under the extremes of tem- 

 perature ; resists the action of water ; set: 

 firmly and promptly with mortar; anc 

 being both cheaper and lighter thar 

 stone, is preferable to it for many kind: 

 of structures — as arches, the walls o 

 houses, etc. 



Brick of good quality exhibits a fine 

 compact, uniform texture when broker 

 across, gives a clear ringing sound wher 

 struck, and is of a cherry red or brownisr 

 color. Three varieties are found in the 

 kiln : Those which form the arches, call 

 ed arch brick, are always vitrified in part 

 and present a grayish, glassy appearance 

 at one end; they are very hard, but brit 

 tie, and of inferior strength, and set badl] 

 with mortar. Those from the interior o 

 the kiln, usually called red and hare 

 brick, are of the best quality. Those 

 from near the top and sides are gener 

 ally under burnt, and are called salmor 

 brick; they have neither sufficien 

 strenght nor durability for heavy work 

 nor the outside courses of walls whicl 

 are exposed to the weather. 



The bricks in general use are Stock 

 Red and Hard, and Merchantable bricl 

 — this latter being part salmon and par 

 red brick. 



Brick presents great diversity in it: 

 strength, arising principally from its great 

 er or less density; the densest made o 

 the same earth being uniformly the 

 strongest. 



It was found on experiment that gooc 

 brick, having the specific gravity of 2,168 

 required 1,200 pounds on a square incl 

 to crush it. 



Machinery is now coming into use 

 in this country for moulding brick 

 it is superior to manual labor, not onl] 



