Summing up the effects of carbonates and other kinds of lime in the kiln, it may be at once said that when present in any other form than as extremely minute particles, they are distinctly to be avoided. The small pellets and large pebbles especially are to be avoided, for the following reasons. Carbonate of lime is made up of lime and carbonic acid; if a lump of this be subjected to great heat and thus calcined, the carbonic acid is driven off, escaping by means of flues, the open chimney, or kiln. The product is lime pure and simple--ordinary builders’ lime. Everyone knows that on the addition of water builders’ lime becomes “slacked,” and eventually, after a fashion, “sets.” Precisely the same thing occurs in the brick-kiln. The raw brick is often composed of pieces of chalk or other limestone, in limestone districts and in areas where boulder clays are largely employed for brickmaking. On being subjected to the heat of the kiln these pieces are promptly reduced to the condition of lime. During the process of conversion considerable expansion takes place, and subsequently contraction, leading to the formation of cracks radiating from the fragments of limestone, the homogeneity of the bricks being at once destroyed. Apart from this, when placed in the open air the lime becomes slacked, and the quality of the brick is seriously impaired. Lime is a highly refractory substance, strongly basic in character, and forms fusible compounds with silica and other acid bodies. It is, therefore, useful as a flux in many earths used in brickmaking, being added to them expressly for that purpose, to the general improvement of the brick. The celebrated Dinas bricks, for instance, are composed of a highly refractory earth containing about 97 per cent. silica, the remainder being lime, oxide of iron, alumina, alkali and water. To render this material fusible and so as to make refractory bricks, from 1 to 3 per cent. of lime is added.