All known methods for chemically purifying woolen stuffs from vegetable fibers depend on the action of acids or substances of acid reaction. The excessive temperature, hitherto unavoidable in the operation, acts injuriously on the woolen fibers, especially during the formation of hydrochloric acid, with which process especially the development of an injuriously high temperature has been hitherto unavoidable. The best method of absorbing the heat developed is in the evaporation of the moisture naturally present in the wool. The patentees find agitation of the fabric and the use of an exhauster during the process of material assistance. The operation maybe successfully performed in two ways--either by acting on the fabric at the ordinary pressure with constant agitation, or by saturation without agitation in a vacuum. For the first method the patentees employ a wooden cylinder with an aperture at one end for inserting and removing the cloth, and having apertures all round to allow free access of air. This cylinder rests on a hollow axle, closed at one end and perforated with holes, through which the acid gas is passed. By the rotation of the cylinder the gas is drawn through the material and the latter exposed to the atmosphere, whereby it gives up a quantity of aqueous vapor.

An average temperature of 30° Cent. is best suited to the operation, and it can be regulated according to the supply of gas by opening or shutting a three-way cock between the gas generator and the revolving cylinder. This process is assisted by the use of an exhauster of the usual construction. When fully saturated, the fabric is allowed to remain until the vegetable fibers are sufficiently friable. The treatment in vacuo is as follows:

The hydrochloric acid gas passes into a vessel of suitable material provided with a perforated false bottom. From under this false bottom a pipe connects with a second similar vessel connected itself with a vacuum pump having a let-off pipe. As soon as the maximum vacuum is attained, the gas is turned on through a three-way cock at a pressure of 40 mm. mercury. The gas fills the first vessel and saturates the cloth. The warmth set free (about 500 calories per kilo, gas) is taken up by the combined water in the wool, as, owing to the low pressure, a quantity of vapor is formed sufficient to take up the heat. This vapor streams through the second vessel at a temperature of 35° Cent., penetrates the material, and passes out through the pump. After saturating the contents of the first vessel the gas passes into the second. AS soon as this is one-quarter or one-third saturated the first vessel is taken out and replaced by a third, which receives the overplus from No. 2 in like manner, and so on. This plan of working prevents gas passing through and damaging the pump. Instead of working under reduced pressure, the desired low temperature can be maintained by passing alternately with the gas currents of air which absorb heat in evaporating the moisture of the material.

The cloth, after saturation by these processes, is left from six to twelve hours in the vessels, after which it is freely exposed to the air until the vegetable particles are friable. As soon as this occurs, the fabrics are washed. It is advantageous to add to the wash water powdered carbonate of baryta, strontia, magnesia, or preferably lime, and subsequently to rinse in pure water. Phosphate of lime containing carbonate may also be employed for neutralizing the acid, and the residue recovered and separated from the organic residues mixed with it.--"H. J.," Journal of the Society of Chemical Industry.