flask are very liable. The lower end of the distilling tube reaches to the eurface of the acid in the flask B. The ammonia contained in the sample is now evolved in the gaseous state and passes over into the standard acid, which must of course be in more than sufficient quantity to neutralize the whole of it. Ebullition is kept up for ten or fifteen minutes, and the apparatus is then left to stand for the same period in order to allow all the ammonia to be absorbed ; the flask is then boiled again for s. minute and allowed to become cool. When cool, the clip is opened and air is blown through to force any remaining gas to pass into the acid ; the tube c is then washed down with distilled water, and the contents of the flask B are titrated with standard alkali (see Alkali metry) to determine the excess of acid. This excess, deducted from the quantity previously introduoed, gives the atnount of acid which has been neutralized by the amtnonia given off. This method, of course, gives only the ammonia contained ready formed in the guano.
(6) Total Nitrogen.—In order to estimate the total amount of nitrogen in the sample hy con verting it into ammonia, 0.5 to 1 grm. is dried in a water-bath and mixed with soda lime in a combustion tube, olosed at one end, about 14 in. long and in. in diameter. A small quantity of a dried mixture of oxalic acid and soda lime is placed in the closed end of the tube, and then the mixture of guano and soda lime is introduced, leaving a space of about 2 in. at the open end to be filled with naore soda lime ; the end ie finally olosed with a stopper having a Varrentrap and Will's nitrogen bulb arrangement fixed in it ; these bulbs contain a sufficient quantity of standard sulphuric acid. The tube is then heated in a combustion furnace; a strong heat is applied to the end containing the oxalic acid, by which means a current of carbonic acid is produced, which drives the ammonia evolved through the tube into the bulbs. When this current slackens, and before the aeid in the bulba has time to run back into the hot tube, the stopper is withdrawn, and the acid solution is washed from the bulbs into a beaker and the excess of acid determined, as in the previous ease, by titrating with standard alkali.
Assay of Gunpowden—An assay of gunpowder comprises the determination of moisture, nitre, sulphur, and charcoal, and ie performed in the following manner :— (1) Moisture.—Weigh out about 75 or 80 grains of the powder, and dry them over concentrated sulphuric acid, or in an air-bath at 40°, until the weight is constant. The loss in weight repre sents the moisture.
(2) Nitre.—Weigh out about the same quantity and moieten it with a little water, tritnrate in name is given to the oxide of the metal barium, BaO, one of the alkaline earths. It has been already described under the above heading in the article on Alkalies,
(p. 232); but some of the salts of this earth, such as the carbonate, nitrate, and sulphate, have become of sufficient commercial importance to demand separate treatment.
Carbonate of Baryta. (Fa., Carbonate de baryte; GER., Kohlensaures Baryt.) Formula, —Carbonate of baryta occurs abundantly in the natural state as the mineral Witherite, in Shropshire, Westmoreland, Cumberland, and Northumberland. It is obtained in an absolutely pure htato by adding an alkaline carbonate to a solution of chloride of barium, or by saturating the hydrate w ith carbonic acid gas ; in either ease, the heavy, white precipitate formed is well washed and dried. It is almost insoluble in water, and is decomposed by acids ; it is also highly poisonous. In the arts, carbonate of baryta is employed as the base of certain delicate colours, and as an ingredient in plate glass Wedgwood ware. In France, it is largely used in the preparation of beetroot sugar. The native carbonate is used in pharmacy for preparing some of the other salts of barium, for which purpose it is sufficiently pure. Only a small quantity is now produced in England.
Nitrate of Baryta. (Fa., Nitrate de baryte ; GER., Barytsalpeter.) Formula, Nitrate of barium is made by neutralizing a hot, dilute solution of nitric acid with carbonate of baryta, and evaporating the solution until crystals are obtained. These are transparent, colourless octahedra, anhydrous, insoluble in alcohol, and requiring about eight parts of cold and three parts of hot water for solution. Its chief use is in pyroteeliny, in the preparation of green fires. It has also been lately employed in the manufacture of explosive agents, as a substitute for nitrate of potassium. (See Explosive Agents.) Sulphate of Baryta. (Fa., Sulphate de baryte ; GER., Schwefelsaures Baryt.)—This salt, the most important of the salts of barium, is found Dative in large quantities, forming the species of mineral termed barites or barytes, and commonly known as heavy-spar, on account of its weight (sp. gr. from 4.3 to 4.7). It is found in Derbyshire and Shropshire, and often occurs in fine tabular crystals. The massive variety found in the mountain limestone of the above counties is sometimes called " cawk " ; it is more frequently found in white or reddish-white masses. In Saxony, it occurs as the mineral stangen-spath, in a columnar form ; and at Bologna, - nodular variety is found, called Bologna stone, which is notable for its phosphorescent powers when heated.