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To Purify Oil of Vitriol

Com-wood, or cork chips, or sawdust are digested mercial sulphuric acid frequently contains in hot sulphuric acid, a mixture of sulphurous nitrous acid, arsenic, and saline matter. and carbonic acids is obtained, which is used These impurities must be removed in order to for bleaching and cleansing purposes. obtain the acid in any high degree of purity. 3866. Pure Gaseous Sulphurous Nitrous acid is removed by adding about Acid. This is evolved during the action of 1½ grains sugar to each fluid ounce of the sulphuric acid on mercury or clippings of copper. It is also obtained pure by heating Nitric acid of less density than 1.42 parts in a glass retort, a mixture of 100 parts black with water and becomes stronger at lower oxide of manganese, and 12 or 14 parts sul- temperatures; but acid of higher specific phur. The gas evolved should be collected in gravity is weakened by exposure to heat. It a receiver over mercury. 3867.

Sulphurous Acid Solution. rapidly oxidizes the metals, and unites with freezes when exposed to extreme cold. It The gas obtained according to the last method is to be passed through water, which is capable of dissolving or absorbing 30 times its bulk of the gas. To avoid waste in preparing the solution, the unabsorbed gas which escapes from the water is usually again passed through water, and the same arrangement repeated through a series of vessels of water so long as any gas escapes undissolved.