No very great improvements in the method of burning mountain limestone have been made for several years, but there are kilns, such as the Hofmann kiln, and calciners which are great improvements on the old forms of kiln. The Hofmann kilns are very large and circular or oval surrounding a chimney stack; they can be divided into twelve or more compartments, each one of which has a door for charging purposes, an opening connecting it with the chimney and covered with a damper, ami holes in the roof for stoking purposes. In starting the kiln all the compartments but one are filled with limestone loosely piled and the doors made up. Fires are made in the empty compartment, and the dampers are all closed with the exception of that in the farthest chamber, so that the flames and hot air have to travel all round the kiln before they escape to the chimney. As the coal burns away slack is fed through the holes in the roof, and when the limestone is fully burnt in the first compartment the damper in the empty compartment is thrown open and the other closed, so that the empty compartment becomes the last in the series, and the first compartment begins to cool down. The coal is now fed through the roof of the second compartment, and this procedure goes on right round the kiln.

The empty compartment is charged as soon as it is cool enough to enter: the first compartment is next emptied and refilled, and so on, emptying and refilling going on all the time. The calciner is made in the usual form of circular kiln, but it has a cone-shaped structure at the bottom, and there are openings all round the circumference of the furnace above the floor level. The limestone and slack are fed in at the top, and as the coal burns away and the limestone contracts during its con» version into lime;it gradually descends, but is prevented settling at the bottom of the furnace by the cone-shaped structure, which directs the material towards the walls of the furnace, and it falls out through the openings above mentioned.