3. Mallet’s Apparatus. This, which is employed in many of the large gas works, is shown in vertical section in the accompanying woodcut. Steam is forced into large receptacles, which are filled with gas water, by which means the carbonate of ammonia is volatilised. When lime, as is sometimes the case, is added, ammonia gas is evolved, and this being conveyed into weak sulphuric acid, sulphate of ammonia is the result. [Illustration] The apparatus consists of two cylindrical boiler-plate vessels, A and B. A is heated directly by the fire, and has a leaden tube, _c_, which dips into the liquid contained in B, this vessel being so placed as to catch the waste heat from the fire. _b_ and _e_ are man-holes; _a_ and _a′_ are stirrers. By means of the tube _d_ the fluid from B can be run off into A. Gas-water is poured into both vessels, and lime added; ammonia is liberated, whilst carbonate of lime and sulphide of calcium are formed, and these latter remain in the vessels after the volatilisation of the ammonia. The vessel D is also filled with ammoniacal water, and when the operation is in action this water, already warmed, is run by the aid of the tube _h_ from D into B. E is a gas-water tank, from which D is filled by means of _g_. The ammonia set free in A is, with the steam, conveyed by the pipe _c_ into B, thence through _c′_ into the wash-vessel C, and thence again through _c″_ into the first condenser, D. The partially condensed vapour now passes into the condensing vessel F, the worm of which is surrounded by cold water. The dilute ammonia is collected in G, and forced by means of the pump (R) into C, from whence it is occasionally removed by means of a syphon into either A or B. The non-condensed ammoniacal gas is carried from G through a series of Wolfe’s bottles, the first bottle (H) containing olive oil, with the object of retaining any hydrocarbons that may be present in the gas; the bottle J contains caustic soda-ley, in order to purify the ammonia and retain impurities; the bottle K is half filled with distilled water. The ammoniacal gas having passed through K, is conveyed to the large wooden tank (lined with lead) L, filled with diluted sulphuric acid, if it is intended to prepare sulphate of ammonia, or with water, if solution of ammonia be required. The vessel L is placed in a tank of water; _i_ is a small pipe for introducing acid, while the tube leading to M serves to carry off any unabsorbed ammonia, M being likewise filled with acid. 4. By means of Rose’s apparatus, the ammoniacal gas-liquor mixed with one third of slaked lime is heated in a boiler to a temperature of from 96° to 100°, the ammoniacal gas evolved being passed into hydrochloric acid, and thence through charcoal into vessels containing from 120 to 150 litres of water, which is converted into liquid ammonia of a sp. gr. 0·920. 5. In Lunge’s apparatus the gas-water is heated in a boiler, and the liberated ammoniacal gas passed into sulphuric acid.