_Barium sulphydrate_ has been put on the market experimentally as an unhairing agent, in the form of a strong solution containing yellow polysulphides, and which deposits crystals of sulphydrate in cold weather. It is more stable than calcium sulphydrate, but, on the whole, does not seem to present any advantages over sodium sulphide. _Realgar or red sulphide of arsenic_, As₂S₂, is made by fusing arsenious acid and sulphur. (Orpiment is As₂S₃, but its action is different from that of realgar.) Mixed with lime it produces calcium sulphydrate and possibly hyposulpharsenite. To produce a rapid and complete reaction it must be mixed with hot lime, and the hotter the mixture is made the more powerful is its unhairing action. Milder forms may be made by mixing cold, or with the aid of hot water only. It is used with great advantage in conjunction with lime in varying proportions for unhairing lamb- and kid-skins for glove-kid and other fine leathers, to which it gives the necessary stretch and softness and cleanness of grain, without the loosening of texture and loss of hide-substance which would be caused by an equivalent amount of ordinary liming. For glove-kid about 0·1-0·3 per cent. of realgar and 5 per cent. of lime is used, reckoned on the green weight of the skin. For painting the flesh side of calf- and lamb-skins 1 part of realgar is mixed with 10 parts of hot lime, made into a paste with water. Calf will unhair in 8 or 10 hours. “Inoffensive” unhairing solution contains a large quantity of arsenic sulphide apparently dissolved in caustic soda, although Moret’s original patent claimed the use of wool-sweat potash only! W. R. Earp[84] has suggested the use of compounds of sulphur and arsenic (thio-arsenates, thio-arsenites, etc.), in 5 per cent. alkaline solution. He prefers to add the compounds to the ordinary lime-liquors, or to manufacture them _in situ_ by adding the proper quantities of arsenious or arsenic acid mixed with one-third of its weight of sulphur to a solution of an alkaline sulphide in lime-liquor. The pelt is not bated or drenched in the ordinary way, but, after unhairing, is passed directly into the tanning liquor to which sulphurous acid has been previously added. [84] Eng Pat., No. 2052, Feb. 12, 1886. There is more danger of injury to the hide from the very prolonged action of weak solutions of sulphides, which tend ultimately to destroy the structure and reduce the fibre to a gelatinous condition, than there is from too concentrated solutions. No danger need, however, be apprehended in the course of any ordinary liming. Arsenical limes are not suited for tainted skins, and they should not be made so strong as to destroy the hair or wool. For methods of analysis of both old and new lime-liquors, see L.I.L.B., pp. 27 to 34.