Illustrated Companion to the Latin Dictionary/Lacuna

This article incorporates text from a publication now in the public domain: Rich, Anthony (1849). The illustrated companion to the Latin dictionary, and Greek lexicon. p. vi. OCLC 894670115. https://archive.org/details/illustratedcompa00rich. 

LACU'NA. A pit sunk underneath the fire of a lime-kiln to receive the ashes which dropped from it, when the kiln was constructed with only one entrance (praefurnium) to its furnace. If there were two entrances, the ashes were removed, when necessary, through one of them, and in that case no lacuna was required. But if there was only a single entrance, such a contrivance was indispensable, because the ashes could not be cleared away without extinguishing or diminishing the fire; and it is a requisite in making lime that the heat should be kept up at a regular and continuous temperature, from the time the furnace is kindled until the whole mass is sufficiently baked. Cato. R. R. 38.