399 B R I 
It may make feme fmall faving in the expence, though 
perhaps not a prudent one, if the brjeks, &c. were of fuch 
a width as to admit a common brick, or piece of plain 
ftone, between the fhoulders of each of thefe bricks ; in 
that cafe, the groove mu ft be made proportionably wider. 
For the purpofe of turning the angles, it may be expe¬ 
dient to have bricks or ffones of fuch fize and fhape as to 
correlpond with each wall refpedtively ; this however is not 
abfolutely necellary, as the groove in the bricks, &c. of 
each wall, where they crofs or meet each other, may be le¬ 
velled, and the bricks lap over, as in the common mode. 
For the purpofe of breaking the joints in the depth of the 
walls, bricks will be required of different lengths, though 
of the fame width. Buildings conftruded with bricks of 
this principle, will require no bond-timber, one univerfal 
bond or tie running through, and connecting the whole 
building together ; the walls of which can neither crack 
nor bulge out, without breaking through the bricks them- 
felves. When thefe bricks are intended to be ufed for 
the conflruCtion of arches, the Tides x>f the grooves and 
the (houlders fhould be radii of the Circle, of which the 
intended arch is to be a fegment. Though, if the circle 
be very large, the difference of the width of the bricks, 
&c. at top and bottom will be fo trifling as to make a 
minute attention to this particular fcarcely, if at all, ne- 
ceffary. When thefe arches are required to be particu¬ 
larly fiat, or are applied in fuch lituations as admit not of 
end-walls, as in the conftrudtion of bridges, &c. it may be 
expedient to have the fhoulders dove-tailed, to prevent 
the arch cracking acrofs, or giving way endwife. If the 
bricks are as wide at the bottom as the top, the manner 
of putting them together by a dove-tail is obvious; when 
not fo wide at the bottom as the top, on one fide of the 
brick, &c. the Tides of the fhoulders muff be parallel, and 
on the other the Tides of the grooves or rabbets muff be 
parallel, fo that the two (ides of the bricks, &c. which fall 
together, may correfpond. In forming an arch, the bricks 
muff be courfed acrofs'the centre on which the arch is 
turned, and a grooved fide of thfe bricks muff face the 
workmen. It may be expedient, though not abfolutely 
neceflary, in laying the firft two or three courfes at lead, 
to begin at the crown, and work downward each way. In 
arch-work, the bricks, &c. may.be either laid in mortar, 
or dry, and the interftices afterwards filled and wedged up 
by pouring in lime-putty, plafter of Paris, grouting, or 
any other convenient material, at the diferetion of the 
workman or builder. It is obvious that arches upon this 
principle, having no lateral prelfure, can neither expand 
at the foot nor fpring at the crown ; confequently they 
will want no abutments, requiring only perpendicular 
walls to be let into, or to reft upon ; and they will 
want no fuperincumbent weight upon the crown to pre¬ 
vent their fpringing up, a circumffance of great import¬ 
ance in many inffances in the conftrudtion of bridges. 
Another advantage attending this mode of arching is, that 
the centres may be ft ruck immediately; fo that the fame 
centre (which in no cafe need be many feet wide, what¬ 
ever may be the breadth of the arch) may be regularly 
(Lifted, as the work proceeds. But the greateft and .moft 
ftriking advantage attending this invention, is the abfo- 
lute fecurity it affords, and at a very reafonabie rate, againft 
the poffibility of fire ; for, from, the peculiar properties of 
this arch, requiring no abutments, it may be laid upon, or 
let into, common walls no ftronger than what are required 
for timbers, of which it will preclude the necellity, and 
faye the expence. 
Befides this improvement by Mr. Cartwright, plans 
have been projected by Worlidge, and others, to excite 
brick-makers to try their (kill in making a kincl of brick, 
or a compofition of clay and land, whereof to form win¬ 
dow-frames, chimney-pieces, door-cafes, and the like. It 
is to be made in pieces faftiioned in moulds, which, when 
burnt, .may be fet together witli a fine red cement, and 
feem as one entire piece, by which may be imitated all 
manner of ftone-work. 
C K. 
With refpefl to the texture and properties of the ma¬ 
terials which enter into the compofition of brick and tile, 
the celebrated Bergman has made the following remarks. 
Softnefs and potofity, he (ays, are the greateft fault in tiles'. 
The water retained in the pores becomes frozen in winter; 
and, as ice occupies a larger fpace than water, theexpan- 
(ion pf the water, at the inftant of its congelation, does not 
fail to fplit and deftroy fuch porous and brittle fpbffances 
as tiles which are ill made. This has lately been reme¬ 
died by covering them with a glaze, which adds confide- 
rably to the expence. Bergman is of opinion, that a 
ftronger heat ufed in the baking would render them fo 
clofe as to abforb very little moifture. This illuftrious 
chemrft did not find that pure clay, or argillaceous earth, 
was fufible either alone or when mixed in any proportion 
with lime, though the addition of the fmalleft quantity of 
filiceous earth brought the mafs into fulion. Neither jvas 
clay fufible with pure quartz alone. Fluor mineral ren¬ 
ders it fufible, as does likewife feld fpar. 
Common clay is fcarcely ever found in a date approach¬ 
ing to purity on the furface of the earth. It ufually con¬ 
tains a large proportion of filiceous earth. Bergman exat- 
rnined feveral clays in the neighbourhood of Upfal, and 
made bricks, which he baked with various degrees of heat, 
fuftered them to cool, immerfed them in water for a con- 
fiderable time, and then expofed them to the open air for 
three years. They were formed of clay and fand. The 
hardeft were thofe, into the compofition of which a fourth 
part of fand had entered. Thofe which had been expofed 
for the (horteft time to the fire were almoft totally deftroy- 
ed, and crumbled down by the action of the air ; fuch as 
had been more thoroughly burned, fuffered lefs damage ; 
and in thofe which had been formed of clay alone, and 
were half vitrified by the heat, no change whatever was 
produced. On the whole, he obferves, that the propor¬ 
tion of fand to be ufed to any clay, in making bricks, muff 
be greater, the more fuch clay is found to contract in burn¬ 
ing; but that the beft clays are thofe which need no fand. 
Bricks fttould be well burned; but no vitrification is ne- 
ceffary when they can be rendered hard enough by the 
mere a&ion of the heat. Where a vitreous cruft might 
be deemed neceffary, he recommends the proje&ion of a 
due quantity of fait into the furnace, which would pro¬ 
duce the effeCt in the fame manner as is feen in the fabri¬ 
cation of the-Englifli pottery, called (tone-ware. 
It is of confiderable importance to examine clay before 
it is made into tiles. This is done in a rough way by the 
manufacturers; but Bergman advifes the following as the 
moft expeditious procels. Nitrous acid poured upon un¬ 
burned clay deteCts the prefence of lime, by producing an 
effervefcence. Calcareous clays, or marks, are often the 
fitted materials for making bricks. In the next place, a 
lump of clay, of a given weight, is to be diffufed in wa¬ 
ter by agitation. The fand will fubfide, and the clay re¬ 
main fufpended. Other wa(hings of the refidue will carry 
off fome clay, and, by due management in this way, the 
land, or quartzofe (natter, may be had feparate. Nitrous 
acid by digeftion will take up the lime from a part of the 
clay, provioufiy weighed, and this may be precipitated by 
volatile alkali. The clay, the fand, and the lime, may 
thus be well enough afeertained by weight, fo as to indi¬ 
cate the quantity of fand oe other material requifite to be 
added in order to form that compound, which, from other 
experiments, may have been found beft adapted to pro¬ 
duce good tiles and bricks. An examination with the mi- 
crofcope will (hew whether the hind contain feld, fpar, or 
other ftones of known figure. The brick-makers in the 
vicinity of London colleCt the refufe cinders and aflies of 
the coal fires of that metropolis, and employ women to fift 
them. The cinders are ufed as fuel in the burning, and 
the fmaller powder, or black allies, enter into the com¬ 
pofition of the bricks inftead.of fand. 
In vol. i. p. 302, of Dr. Percival’s Effays, we have the 
following experiment of the efiefts of bricks on water. 
“ Two or three pieces of common brick were fteeped four 
days 
