The manufacture of waterproofed materials for clothing has attained considerable import ance. The fact, however, must be recognized that the results generally obtained are not alto gether satisfactory, especially from a hygienic point of view. Absolute waterproofing cannot be obtained without wholly closing the pores of the tissue; thus prepared it is an efficacious protection from rain and from contact with water, in certain cases is of real service, but inconveniently prevents ventilation. While the garments are made watertight they are at the same time made airtight. The perspiration and natural moisture of the body arc not allowed to escape, but are held in saturation in the cloth ing, rendering it impure, damp and uncomfort able. The body is kept damp, and upon remov ing the outer garments the wearer is liable to chills and colds, hence, such waterproofing is unsuitable for prolonged personal wear.
The most diverse substances can be used for waterproofing textiles, if they are soluble in a liquid other than water, and can be spread over the surface of the material,— if they possess a certain suppleness, and neither alter the fibre nor the color of the tissue. Wax, balsamic gums, isinglass, spermaceti, metallic soaps dis solved in essential oils, a solution of shellac with borax are employed in waterproofing tis sues. The cloth, whether of silk, cotton, flax or wool, is usually rendered waterproof by the application of some solution of any of these substances to one or both surfaces. In many of the earlier processes, the cloth was im mersed in a liquid, so as to become saturated with the waterproofing agent. An early pat ent was obtained for a method of rendering cloth waterproof without concealing its textile surface; the cloth in the first place is satu rated with a waterproof composition; it is then dried on one side to form a hard film, while the other side is kept moist, and is afterward deprived of its composition by means of spirits of turpentine.
Frequently silk tissues are waterproofed by the use of gelatine rendered insoluble by as alumina soap. The material is impregnated by passing it through cylinders covered with swan skin, afterward being steam dried. Woolen tis sues are passed through a solution of acetate of alumina obtained by treating ordinary alum with acetate of lead. The process most exten sively in use at the present day is the acetate of alumina treatment. The fabric is steeped in the acetate solution for 12 hours, the tem perature being kept at about 95 degrees, special care being taken that it shall not reach 100 de grees. Much difficulty in securing an even dis tribution of the acetate throughout the fabric is avoided by the use of the a machine which takes the cloth on a reel and passes it continuously through a vat containing the chemi cal, winding it upon another reel. When it has
all passed the machine reverses and rewinds the cloth on the first reel; repeating this alter nation again and again. By this process the time of saturation is reduced to five hours. A still more effective method of saturation is by the vacuum process. The reel of cloth is placed in an airtight drum and the air is exhausted. The acetate liquor is then allowed to flow in, filling the cylinder. Air pressure to the ex tent of two and one-half to three atmospheres is applied, and allowed to remain for 45 min utes, when the operation is complete. The cloth then goes to the drying room where the temperature is kept well above 100 degrees, in order that the acetate may be changed by the heat to the insoluble basic acetate of alumina. In this condition the fabric is sufficiently water proof for most purposes of wearing apparel. If it is required that it be absolutely water proof, it may be made so by immersion in a 5 per cent solution of soap. An insoluble aluminum soap is formed on the fibre of the textile and adheres firmly. The fabric will now have a slippery feel, and this is quite ob jectionable. It is readily removed, however, by passing the goods through a solution of common alum of the strength of 1 degree or one and degrees Beaume. With some manufacturers it is a practice to add india rub ber or paraffin to fortify the protection given by the insoluble aluminum soap. This is readily accomplished, as the soap solution easily forms an emulsion with melted paraffine or with a solu tion of rubber in a mixture of linseed and palm oils. A highly recommended formula directs that chopped-up India rubber be dis solved in twice its weight of a hot mixture of petroleum and linseed oil; and that to this be added three times its weight of Japan wax. %Vhen well mixed, a small quantity of liver of sulphur is to he worked in. This mass is then to be stirred into a boiling mixture of Wan. linseed oil and resin. Finally the whole is to be saponified to a neutral soap with caustic potash lye. The completed mixture should show a 10 per cent content of rubber and from 6 to 10 per cent of palm oil. After immer sion, the fabric is calendered by polished steel rolls under heavy pressure. Lmen, hemp and cotton require heavier pressure than wool or silk. In this calendering operation care is seeded to avoid such extreme pressure that the textile fibres are crushed. Casein is sometimes used in waterproofing certain textiles and col lodion also, bat rarely.