4(5 
LAC 
LAC 
LAE 
lour. The basis of lacquers is a solution of 
the resinous substance called seed-lac in spi- 
rit of wine. The spirit ought to be very 
much concentrated, in order to dissolve much 
ot the lac. For this purpose, some authors 
direct dry potass to be thrown into the spirit. 
I his alkali attracts the water, with which it 
forms a liquid that subsides distinctly from the 
spirit at the bottom of the vessel. From this 
liquid the spirit may be separated by decan- 
tation. By this method the spirit is much 
concentrated; but, at the same time, it be- 
comes impregnated with part of the alkali, 
which depraves its colour, and communicates 
a property to the lacquer of imbibing mois- 
ture from the air. These inconveniences may 
be prevented by distilling the spirit ; or, it 
the artist has not an opportunity of perform- 
ing that process, he may cleanse the spirit, in 
a great measure, from the alkali, by adding 
to it some calcined alum; the acid of which 
’Uniting with the alkali remaining in the spirit, 
forms with it -a vitriolated tartar, which, not 
being soluble in spirit of wine, falls to the 
bottom together with the earth of the decom- 
posed alum. To a pint of the purilied spirit, 
.about three ounces of powdered shell-lac are 
to be added ; and the mixture to be digested 
during the same day with a moderate heat. 
The liquor ought then to be poured off, strain- 
ed, and cleared by settling. This clear li- 
quor is now lit to receive the required colour 
from certain resinous colouring substances, 
the principal of which are gamboge and an- 
notto ; the former of which gives a yellow, 
and the latter an orange colour. In order to 
.give a golden colour, two parts of gamboge 
are added to one of annotto; but these co- 
louring substances may be separately dissolv- 
ed in the tincture of lac, and the colour re- 
quired may be adjusted by mixing the two 
solutions in different proportions. When sil- 
ver leaf or tin is to be lacquered, <i larger 
quantity of the colouring materials is requi- 
site than when the lacquer is intended to be 
laid on brass. 
LACTEAL vessels. See Anatomy. 
LACTIC acid. If milk be kept for some 
time it becomes sour. The acid which then 
appears in it was first examined by Scheele, 
and found by him to have peculiar properties. 
It is called lactic acid. In the whey of milk 
this acid is mixed with a little curd, some 
phosphat of lime, sugar of milk, and muci- 
lage. All these must be separated before the 
acid can be examined. Scheele accomplish- 
ed this by the following process : 
Evaporate .a quantity of sour whey to an 
eighth part, and then filtrate it: this sepa- 
rates the cheesy parts. Saturate the liquid 
with lime-water, aud the phosphat of lime 
precipitates. Filtrate again, and dilute the 
liquid with three times its own bulk of water ; 
then let fall into it oxalic acid, drop by drop, 
to precipitate the lime which it has dissolved 
from the lime-water; then add a very small 
quantity of lime-water., to see whether too 
much oxalic acid has been, added. If there 
bas, oxaL.t of lime immediately precipitates. 
Evaporate the solution to the consistence of 
honey, pour in a sufficient quantity of alco- 
ibohol, and filtrate again ; the acid passes 
through dissolved in the alcohol, but the su- 
gar of milk and every other substance remain 
behind. Add to the solution a small quan- 
tity of water, aud distil with a small heat, the 
alcohol passes over, and leaves behind the 
lactic acid dissolved in water. 
This acid is incapable of crystallizing: 
when evaporated to dryness, it deliquesces 
again in the air. When distilled, water comes 
over first, then a weak acid resembling the 
tartaric, then an empyreumatic oil mixed 
with more of the same acid, and, lastly, car- 
bonic acid and carbureted hydrogen gas : 
there remains behind a small quantity of 
charcoal. 
The combinations which this acid forms 
with alkalies, earths, and metallic oxides, are 
called lactats, which see. 
All that is known concerning these salts are 
the following facts, ascertained by Scheele. 
When saturated with fixed alkalies, it gave 
salt.-, which were deliquescent and soluble in 
spirit of wine. It formed deliquescent salts 
with ammonia, with barytes, with lime, and 
alumina ; but with magnesia it formed small 
crystals, which however at length deliquesced. 
This acid had no effect on bismuth, cobalt, 
j antimony, tin, mercury, silver, and gold. It 
dissolved zinc and iron ; and it produced 
! with these metals hydrogen gas. Zinc was 
the only metal with which it crystallized. 
Copper" rendered this acid first slightly blue, 
then green, and lastly _a deep blue; but no 
crystals w ere formed. Digested upon load it 
became sweet, but did not crystallize, 
LACTUCA, the lettuce,' a genus of the 
polygamia aqualis order, in the syngenesia 
class of plants, and in the natural method 
ranking under the 49th order, composite. 
The receptacle is naked; the caljx imbri- 
cated, cylindrical, with a membranaceous 
margin ; the pappus is simple, stipated, or 
stalked. There are 1 1 species, most of which 
are plants of no use, and never cultivated but 
in botanic gardens for variety. That com- 
monly cultivated in the kitchen-garden is the 
sative, which includes the following varieties : 
1. The common or garden lettuce. 2. Cab- 
bage lettuce. 3. Silesia lettuce. 4. Dutch 
brown lettuce. 5. Aleppo, or sperm lettuce. 
0. Imperial lettuce. 7. Green capuchin let- 
tuce. 8. Versailles, or upright white cos let- 
tuce. 9. Black cos. 10. Red cos. 11. Red 
capuchin lettuce. 12. Roman lettuce. 13. 
Prince lettuce. 14. Royal lettuce. 15. Egyp- 
tian cos lettuce. 
The first of these sorts is very common in 
all gardens, and is commonly sown for cutting 
very young, to mix with other salad herbs in 
spring ; and the second, or cabbage lettuce, 
is only this mended by culture. The first 
crop should be sown in February, in an open 
situation ; the others at three weeks distance ; 
but the later ones under covert, but not un- 
der the drippings of trees. The Silesia, im- 
perial, royal, black, white, and upright cos 
lettuces, may be first sown in the latter part 
of February or the beginning of March, on a 
warm light soil, and in an open situation : 
when the plants are come up, they must be 
thinned to 15 inches distance every way; 
they will then require no further care than 
the keeping them Clear of weeds; and the 
black cos, as it grows large, should have its 
leaves tied together to whiten the inner part. 
Succeeding crops of these should be sown in 
April, May, and June ; and towards the latter 
part of August they may be sown for a winter 
crop, to be preserved under glasses, or in a 
bed arched over with hoops and covered with 
mats. The most valuable of all the English 
lettuces are the white cos, or the Versailles*, 
the Silesia; and the Egyptian cos. The 
brown Dutch and the green capuchin are very 
hardy, and may be sown late under walls, 
where they will stand the winter, and be va- 
luable when no others are to be had. The 
red capuchin, Roman, and prince lettuce, are 
very early kinds, and are sown for varietv ; 
as are also the Aleppo ones for the beauty" of 
their spotted leaves. 
The several sorts of garden lettuces are 
very wholesome, emollient, cooling salad 
herbs, easy of digestion, and somewhat loos- 
ening the belly. Most writers suppose that 
they have a narcotic quality ; and indeed in 
many cases they contribute to procure rest : 
this they effect by abating heat, and relaxing 
the fibres. The seeds are in the number of 
the four lesser cold seeds. 
LACUNAR. See Architecture. 
LADDERS, scaling, in the military art, 
are tised in scaling when " a place is to he 
taken by surprise. They are made several 
ways : here we make them of Hat staves, so 
that they may move about their pins, and 
shut like a parallel ruler, for conveniently 
carrying them : the French make them of se- 
veral pieces, so as to be joined together, and 
to he made of any necessary length : some- 
times they are made of single ropes, knotted 
at proper distances, with. iron hooks at each- 
end, one to fasten them upon the wall above, 
and the other in the ground ; and sometimes 
they are made with two ropes, and staves be- 
tween them, to keep the ropes at a proper 
distance, and to tread upon. When they are 
used in the action of scaling walls, they ought 
to be rather too long than too short, and to 
be given in charge only to the stoutest of the 
detachment. The Soldiers should carry these 
ladders with the left-arm passed through the 
second step, taking care to hold them up- 
right close to their sides, and very short be- 
low, to prevent any accident in leaping into 
the ditch. 
The first rank of each division, provided 
with ladders, should set out with the rest at 
the signal, marching resolutely with their fire- 
locks slung, to jump into the ditch : when 
they are arrived they should apply their lad- 
ders against the parapet, observing to place 
them towards the salient angles rather than 
the middle of the curtin, because the enemy 
have less force there. Care must be taken 
to place the ladders within a foot of each 
other, and not to give them too much or too 
little slope, so that they may not be over- 
turned or broken with the weight of the sol- 
diers mounting upon them. 
The ladders being applied, those who have 
carried them, and those who come after, 
should mount up, and rush upon the enemy 
sword in hand: if he who goes tir-t happens 
to be overturned, the next should take care 
not to be thrown down by his comrade ; hut, 
oh the contrary, immediately mount himself, 
so as not to give the enemy time to load his 
piece. 
As the soldiers who mount first mav be 
easily tumbled over, and their fall may cause 
the attack to fail, it would perhaps be right 
to protect their breasts with the tore parts of 
cuirasses; because if they can penetrate the 
rest may easily follow, 
LADY’S smock. See Cardemjne. 
Lady’s slipper. See Cypripedium. 
LAETIA, a genus of the monogynia or- 
11 
