LABORATORY. This name is given to the room in which chemical operations are performed. The requisites for the proper ar rangement of and the necessary instruments for a laboratory maybe seen at length in Pro fessor Faraday's ' Chemical Manipulation.' LAC, is a resinous substance, which in the East Indies flows front certain trees in the state of a milky fluid, on account of the punc ture made by a small insect, the Coccus finis, in their branches, in order to deposit its ova. The trees are principally the Ficus indica, Fi cus religiosa, and Rhamans jujuba. There are three kinds of lac known in commerce, distin guished by the names of Stick Lac, Seed Lac, and Shell Lac. Stick Lac is the substance in its natural state ; it is of a reddish colour, and incrusts small twigs ; when broken off and boiled in water, it loses its red colour, and is then termed Seed Lac ; and, when melted and reduced to the state of thin plates, it is called Shell Lac, which has a yellowish brown colour.
Several chemical substances are produced from Lac. Laccin is the substance which re• mains after the lac has been repeatedly di gested in alcohol and water. It is insoluble in water, alcohol or ether. Laccic Acid sepa rates from solution in water, by spontaneous evaporation, in crystalline grains. With the alkalies and with lime it forms salts which are soluble in alcohol and in water, and are deli quescent. Coati/id/in, or the colouring mat ter of stick-lac is similar to that of cochineal, is used for the same purposes, and yields a scarlet colour little inferior to it.
Lac Dye and Lac Lake, two preparations of lac which are manufactured in the East Indies are used to a very considerable extent in scar let dyeing.