l a a 
LAC 
L A 
0 
41 
©eiain, are useful for stirring acid and cor- 
rosive liquids' and a stock of cylindrical 
tubes of various sizes, is required for occa- 
sional purposes. It is necessary also to be 
provided with a series of glass measures, 
graduated into drachms, ounces", and pints. 
Accurate beams and scales, of various 
sizes, with corresponding weights, some of 
which are capable of weighing several pounds, 
while the smaller size ascertain a minute 
Fraction of a grain, are essential instruments 
in t.Ve chemical laboratory. So also are 
I mortars of different materials, such as of glass, 
| porcelain, agate, and metal. W ooden stands 
I of various kinds for supporting receivers, 
should be provided. For purposes of this 
sort, and for occasionally raising to a proper 
height any article of apparatus, a series of 
blocks, made of well-seasoned wood, eight 
inches (or any other number) square, and 
respectively eight, four, two, one, and half 
an inch in thickness, will be found extremely 
useful ; since by combining them in differ- 
ent ways, no less than thirty-one different 
heights may be attained. 
The blowpipe is an instrument of much 
utility in chemical researches. A small one, 
invented by Mr. Pepys, with a flat cylindri- 
cal bjx for condensing the vapour of the 
| breath, and for containing caps, to be oc- 
casionally applied with apertures of various 
sizes, is perhaps, the most commodious 
form. A blowpipe, which is supplied with 
air from a pair of double bellows, worked 
by the foot, may be applied to purposes 
that require both hands to be left at liberty, 
and will be found useful in blowing glass, 
and in bending tubes. The latter purpose, 
however, may be accomplished by holding 
them over an Argand’s lamp with double 
wicks-. 
Laboratory, signifies also in military 
affairs, that place where all sorts of fire-works 
are prepared both for actual service, and for 
pleasure, viz. quick matches, fusees, portfires, 
grape-shot, case-shot, carcases, hand-gre- 
nades, cartridges, shells filled and fusees 
fixed, wads, &c. 
LAB R US, a genus of fishes of the order 
thoracici : the generic character is, teeth strong 
and subacute: the grinders sometimes, as in 
the spari, convex and crowded : lips thick 
and doubled: rays of the dorsal fin, in some 
species, elongated into soft processes. Gill- 
covers unarmed and scaly. 
Labrus hepafcus, - snout rather pointed : 
teeth small: palate furnished with a rough 
bone. Native of the Mediterranean, some- 
times wandering into rivers. There are 41 
species belonging to this genus, all of which 
are but imperfectly understood. 
LABOURER. See Master and Ser- 
vant. 
LABYRINTH, in gardening, a winding 
mazy walk between hedges, through a wood 
or wilderness. The chief aim is to make 
the walks so perplexed and intricate, that a 
person may lose himself in them, and meet 
with as great a number of disappointments 
as possible. They are rarely to be met 
with, except in great gardens ; as Versailles, 
Hampton-court, &c. 
LAC, an appellation given to several che- 
mical preparations. 
Lac. This resin exudes from the tree 
VOL. II. 
called dm croton Iacciferum, when punctured 
by an insect. For the history of its fonua- 
licp, and the uses to which it is applied by 
the insects, the reader is referred to the 
article Gum, &c. It is a substance of a 
deep-red colour verging on brown, and 
semitransparent, and distinguished by various 
names according to its purity. It possesses 
the properties of a resin, and is the basis of 
many varnishes, and of the finest kinds of 
sealing-wax. 
Lac sulphuris, is obtained by precipitating 
sulphur, when in combination : it is com- 
posed of sulphur united to a little water. 
LACIiERNALIA, a genus of the class 
and order hexandria monogynia. The cor. 
is six-parted, three outer petals difform ; 
caps, three-winged; cells many-seeded; 
seeds globular, affixed to the recept. There 
are twelve species, chiefly bulbs of the 
Cape. 
LACTATS, in chemistry, a genus of salts 
but little known. 1. Lactat of potass, a de- 
liquescent salt soluble in alcohol. 2. Lactat 
ot soda. This salt does not crystallize. It 
is soluble in alcohol. 3. Lactat of ammonia. 
Crystals which deliquesce. Heat separates 
a great part of the ammonia before destroy- 
ing the acid. 4. Lactat of barytes ; lime ; 
alumina ; all deliquesce. 
LACCIC acid. About the year 17S6, 
Dr. Anderson of Madras mentioned, in a 
letter to the governor and council of that 
place, that nests of insects, resembling small 
cowry shells, had been brought to him from 
the woods by the natives, who ate them with 
avidity. These supposed nests lie soon af- 
terwards discovered to be the coverings of 
the females of an undescribecl species of coc- 
cus, which he shortly found means to propa- 
gate with great facility on several of the trees 
and shrubs growing in his neighbourhood. 
On examining this substance, which he 
called white lac, he observed in it a very 
considerable resemblance to bees’ wax ; he 
noticed also, that the animal which secretes 
it' provides itself by some means or other 
with a small quantity of honey, resembling 
that produced by our bees; and in one of 
his letters he complains, that the children 
whom he employed to gather it were tempt- 
ed by its sweetness to eat so much of it, as 
'materially to reduce the produce of his crop. 
Small quantities of this matter were sent 
into Europe in 17S9, both in its natural 
state and melted into cakes; and in 1793 
Dr. Pearson, at the request of sir Joseph 
Banks, undertook a chemical examination of 
its qualities, and his experiments were pub- 
lished in the Philosophical Transactions for 
1794. 
A piece of white lac, from 3 to 15 grain 
in weight, is probably produced by each in 
sect. These pieces are of a grey colour 
opaque, rough, and roundish. When whit 
lac was purified by being strained througl 
muslin, it was of a brown colour, brittle 
hard, and had a bitterish taste. It melted ii 
alcohol, and in water of the temperature c 
145°. In many of its properties it resemble 
bees’ wax, though it differs in others; an< 
Dr. Pearson supposes that both substance 
are composed of the same ingredients, bu 
in different proportions. 
1. Two thousand grains of white lac weri 
exposed in such a degree of heat as was jus 
sufficient to melt them. As thev grew sol 
F 
and fluid, there oozed out 550 grains of a 
reddish watery liquid, which smelted like 
newly baken 'bread. To this liquid Dr. 
Pearson has given the name of laccic acid, 
2. It possesses the following properties: 
It turns paper stained with turnsole to a 
red colour. 
After being filtred, it has a slightly saltish 
taste with bitterness, but it is not at ail sour. 
V hen heated, it smells "precisely like 
newly baken hot bread. 
On standing, it grows somewhat turbid, 
and deposits a small quantity of sediment. 
Its specific gravity at the temperature of 
60° is 1.025. ‘ 
A little of it having been evaporated till 
it grew very turbid, afforded on standing 
small needle-shaped crystals in mucilaginous 
matter. 
I wo hundred and fifty grains of it were 
poured into a very small retort and distilled. 
As the liquor grew warm, mucilage-like 
clouds appeared ; but as the heat increased 
they disappeared again. At the temperature 
of 200° the liquor distilled over very fast : 
a small quantity of extractive matter remain- 
ed behind. The distilled liquor while hot 
smelled like newly baken bread, and was 
perfectly transparent and yellowish. A shred 
of paper stained with turnsole, tvhich had 
been put into the receiver', was not redden- 
ed ; nor did another which had been im- 
mersed In a solution of sulphat of iron, and 
also placed in the receiver, turn to a blue 
colour upon being moistened with the solu- 
tion of potass. 
About 100 grains of this distilled liquid- 
being evaporated till it grew turbid, after 
being set by for a night, afforded aciculajf 
crystals, which under a lens appeared in a 
group not unlike the umbel of parsley. The 
whole of them did not amount to the quartet 
of a grain. They tasted only bitterish. 
Another 100 grains being evaporated to 
dryness in a very low temperature, a black- 
ish matter was left behind, which did not en* 
tirely disappear on heating the spoon con- 
taining it very hot in the naked fire ; but on 
heating oxalic acid to a much less degree, 
it evaporated and left not a trace behind. 
Carbonat of lime dissolved in this distilled 
liquid with effervescence. The solution 
tasted bitterish, did not turn paper stained 
with turnsole red, and on adding to it car- 
bonat of potass a copious precipitation en* 
sued. A little of this solution of lime and of 
alkali being evaporated to dryness, and the 
residuum made red-hot, nothing remained 
but carbonat of lime, and carbonat of potass; 
This liquid did not render nitrat of lime 
turbid, but it produced turbidness in nitrat 
and muriat of barytes. 
To 500 grains of the reddish-coloured li- 
quor obtained by melting white lac, carbonat 
of soda was added till the effervescence 
ceased, and the mixture was neutralized ; 
for which purpose three grains of the car- 
bonat were necessary. During this combi- 
nation a quantity of mucilaginous matter, 
with a little carbonat of lime, was precipi- 
tated. The saturated solution being filtrated 
and evaporated to the due degree, afforded 
on standing deliquescent crystals, which q*» 
exposure to fire, left only a residuum of car-' 
bonat of soda. 
Lime-water, being added to this reddish- 
coloured liquor- produced a light purple 
