Besides the above methods, the alkaline carbonates are analysed, by the loss of carbonic anhydride (carbonic acid) they suffer, by being decomposed by a strong acid. The best method in use is that of MM. Fresenius and Will, and depends on the same principle, and is performed in a similar manner and in a similar apparatus to that described under ACIDIMETRY; the only difference being that here the uses of the small tube (_e_) is dispensed with, and that the alkali is tested under the form of carbonate, instead of bicarbonate. _Oper._ The smaller flask (_B_) is about half filled with concentrated sulphuric acid, and the sample of alkali, in solution (under the form of carbonate), being placed in the larger flask (_A_), water is added until it is about one third full. The tubes are then fitted into the apparatus quite air-tight; the end of the tube (_b_) is fastened with a piece of wax, and the whole is very carefully weighed. The apparatus is now removed from the scales, and a perforated cork, or a small piece of india-rubber tube, being temporarily applied to the end of the tube (_h_), a few bubbles of air are sucked out of the flask (_B_) by means of the lips; the consequence of which is, that on removing the mouth the acid in (_B_) ascends to a certain height in the tube (_c_). If in a short time this little column of liquid maintains its height in the tube, it is a proof that the apparatus is perfectly air-tight, and as it should be. Suction is now again cautiously applied to the tube (_h_) and a little of the acid in (_B_) made to flow over into the flask (_A_), the quantity being proportionate to the vacuum produced by suction, and capable of being regulated at will. No sooner does the acid come into contact with the carbonate in the flask (_A_) than the evolution of carbonic acid commences, and this, from the construction of the apparatus, having to pass through the concentrated sulphuric acid, is rendered quite dry before it can escape by the tube (_d_) into the atmosphere. Whenever the effervescence flags, a little more acid is sucked over, until the whole of the carbonate is decomposed; after which an additional quantity is made to pass into (_A_), so as to raise the temperature considerably, for the purpose of expelling all the gas absorbed by the fluid during the operation. As soon as this is effected, the wax is removed from the aperture (_b_), and suction applied to (_h_), until all the carbonic acid in the apparatus is replaced by atmospheric air. The whole is now allowed to cool, and (together with the piece of wax removed) is again accurately weighed. The loss of weight gives the exact amount of dry carbonic anhydride, or anhydrous carbonic acid, which was contained in the specimen, from which the weight of PURE ALKALI is readily estimated, as every 22 gr. of dry carbonic acid gas evolved represents exactly 31 gr. of pure SODA, 47 gr. of pure POTASSA, &c. &c.; these numbers being the