430 
PIGMENT. 
dined pofition to the roller, and turning on pivots at dd. 
G is a llide-board to draw out occafionally, to clean, &c. 
if any particles of paint fhould fall from the roller, and 
which alfo forms itfelf for the plate I-] to catch the colour 
as it falls from the taker-off. F is a drawer, forthepur- 
pofe of containing curriers’ (havings which are the heft 
things for cleaning the cylinder and muller, when a frefh 
colour is wanted to be ground. 
The colour, being firft pul verifed in a mortar, or roughly 
ground in a large colour-mill above defcribed, is applied 
in proper quantities, by means of a knife, to the front of 
the cylinder above the taker-off'; and, by means of the 
winch-handle G, the mill is worked, until the colour, by 
palling between the revolving (tone and muller, is fuffi- 
ciently ground; when the taker-off D, which during the 
operation lay back, is turned againft the ftone, the 
winch-handle is turned the reverie way for a few re¬ 
volutions, in order to fcrape off the colour which falls 
into the difti H. 
In the Philofophical Tranfaft ions, N° 87, p. 5059, a 
mill is defcribed as having been ufed by Dr. Langelot, 
for grinding leaf-gold to powder, for the fanciful pur- 
pofe of preparing aurum potabile. The principles of this 
mill were fome years ago, found applicable to the grind¬ 
ing of dry indigo in Mr. Taylor’s manufactory at Man- 
chefter, and were alfo found by Mr. Rawlinfon, above 
mentioned, to be the heft adapted for finely pulverizing 
the dry colours intended to be ground with oil or water 
in bis colour-mill. This Ample mill is defcribed and 
figured by Mr. R. on the fame engraving with the prece¬ 
ding; and is reprefented at fig. 3. where L is a marble 
mortar, nicely formed and polifhed ; M is a muller nearly 
in the form of a pear, having an iron axis fixed into its 
upper end, which is bent into the form of a crank at P 
to ferve as a handle for turning the muller: the axis is 
fixed, when in ufe, into two collars O O, in beams of 
wood N N, fo as to revolve eafily and truly in the axis of 
the mortar. This muller is drawn feparately at fig. 4, 
which flows a flit that is made through it, almoft divi¬ 
ding it into two parts: this flit is of ufe in collecting the 
colour which is grinding, and bringing it continually un¬ 
der the muller. By means of the fiat perforated weights 
R, on the top of the axis, any required prefl'urecan be 
applied upon the muller. 
For grinding indigo, or fuch fubflance, in a dry ftate, 
in this mill, the muller being placed in the mortar, and 
fecured in the oak pieces by the pins, the indigo to be 
ground is thrown above the muller into the mortar; on 
turning the handle of the axis, the indigo in lumps falls 
into the groove cut through the muller, and is from 
thence draw n under the aCtion of the muller, and propelled 
to its outer edge within the mortar, from whence the 
coarfer particles again fall into the groove of the muller, 
and are again ground under it; which operation is conti¬ 
nued, till the whole of it is ground to an impalpable 
powder : the muller is then eafily removed, and the co¬ 
lour taken out. A wooden cover, in two halves, with a 
hole for the axis, is ufually placed upon the mortar, du¬ 
ring the operation, to prevent any lofs to the colour, or 
bad effect to the operator. Tranf. of the Soc. of Arts, vol. 
xxii. 1804. 
For prelerving the health of fuch colour-men and paint¬ 
ers as (till prefer the common ftone and muller for grind¬ 
ing their colours, M. Boulard of Lyons, in the Journal 
de Phyfique, recommends an apparatus reprefented at fig. 
5. wherein the ltone, and its table A B, is furrounded by 
a clofe-fided cafing of boards C C, fitted to the floor of 
the room, and leaving a fpace of about -j^-th of an inch 
wide all round the table fupporting the Hone; this is for 
emitting a current of freflt air, which is to be Supplied by 
a pfpe D, extending from a hole in the floor under the 
cafe, to the outward air in fome moft convenient place. 
Over the ftone a glazed pyramid E E and metal tube F is 
fupported by the irons G and braces H, H, H, or by other 
more convenient means, fo that the pyramid E E projects 
on all fides, about three inches beyond the ftone; and at 
a height above the fame no greater than is fufficient for 
the free admifiion of the workman’s arms to work the 
muller, and with his pallet-knife to fcrape together the 
colour when requifite, and which he will be able perfectly 
to fee to do, through the glafs in the frame, without 
inhaling the vapour from the colours, but which are to 
be made to afcend through the tube F, and pafs off into 
the open air through the tube M M, by means of a fmall 
ftove, 1 I, clofely jointed to the tubes F and M, which is 
to be kept burning during the hours of work, in order to 
produce a current between the pipes D andM, that may 
effectually carry off the contaminated air which has been 
in contaCt .with the colours on the ftone, along with their 
effluvia. K reprefents the door of the fire-place, and L 
that of the afh-hole of the ftove, both contrived to fliut 
very dole. In the pipe F, a regilter N fhould be made 
for regulating the burning of the ftove, by the admifiion 
of more or lefs air thereto through the pipe F. If defi¬ 
nable, the clofe pipe F may be conducted into the fire¬ 
place of any ftove or fire in the apartments above, or it 
may even defcend by a proper curvature, fo as to admit 
of the ftove 11 being placed on the ground, and applied 
to any ufeful pnrpole, as the boiling of oil, or heating an 
adjoining room, &c. 
In order that the furnace may produce its effeCts pro¬ 
perly, the doors of it mud be clofe fhut, and the room in 
which this contrivance is placed muft be only of a mid¬ 
dling fize, and well clofed. The fmall quantity of air 
which will come in through the interftices of the doors 
and windows, will do no harm ; on the contrary, as it 
will be drawn under the pyramid, it will carry off thofe 
vapours which the workman, by the motion of his arm, 
may have caufed to efcape. 
Monf. Boulard, in anfwering objections againft his 
apparatus, fays, “ I have tried the effeCt of the contrivance 
I propofe; and found that, by means of as much char¬ 
coal as ferved me to fill the furnace twice, I could grind 
verdegris, (a colour which furnifhes the moft dangerous 
vapours, and the moft offenfive fmell,) for the fpace of 
three hours, without the fmalleft inconvenience. Several 
very delicate perfons, who came into the room during the 
operation, affured me that they did not perceive any 
difagreeable fmell, and that the contrivance appeared to 
them to anfwer the end propofed in the moft complete 
manner. 
“I afterwards made the following experiment. To 
render the current of air which rifes around thegrinding- 
ftone perceptible, I put into the wooden cafe, under the 
ftone, a chafing-difn with a fmall fire in it, on which I 
threw fome powdered fugar. A thick fmoke arofe round 
the ftone; and was perceived to pafs rapidly into the 
pyramid, being drawn that way by the current of air 
which pa fled through the furnace. This current of air 
and fmoke was fo rapid, that I could by no means alter 
its courfe, or direCt it to the outfide of the pyramid. 
“I fee but one reafonable objection to wdiat I have here 
propofed. It may be faid, that in fummer the furnace 
may occafion a degree of heat in the room which may be 
very difagreeable; or (admitting that not to happen) 
the furnace may not occafion fo ftrong a current of air 
at that feafon of the year as at others. The firft part of 
this objection I confider asabfolutely void of foundation ; 
a very fmall quantity of fuel ferves to keep up the fire, 
the beat from which is mild and temperate, and much 
lels than that in which many workmen are obliged to 
perform their relpeCtive operations. But, were it greater, 
an increafe of heat would furely be lefs dangerous than 
the vapours arifing from many colours. With refpeCl to 
the current of air in fummer, I have realon to think it 
would always be fufficient to produce the deiired effect. 
If it fhould nor, I propofe to employ, inftead of the fur¬ 
nace, two pair of Angle bellows, ot a middling fize, which 
a child might work by means of a beam or lever. Thele 
bellows fhould be placed oppofite each other, and near 
