Without considering the methods by which cloth is waterproofed with rubber, there are several processes in practical use by which cloth is rendered non-absorbent of water - and for all practical purposes waterproof - without materially affecting its colour or appearance, greatly increasing its weight, or rendering it entirely air-proof. These depend mainly upon the reaction between 2 or more substances, in consequence of which a substance insoluble in water is deposited in the fibres of the cloth.
(1) Lowry's process. 2 oz. soap, 4 oz. glue, 1 gal. water. Soften the glue in cold water, and dissolve it together with the soap in the water by aid of heat and agitation. The cloth is filled with this solution by boiling it in the liquid for several hours, the time required depending upon' the kind of fibre and thickness of the cloth. When properly saturated, the excess of liquid is wrung out, the cloth is exposed to the air until nearly dry, then digested for 5-12 hours in the following solution: 13 oz. alum, 15 oz. salt, 1 gal. water. It is finally wrung out, rinsed in clean water, and dried at a temperature of about 80° F. (27° C).
(2) Pant's process requires a small quantity of oil, but in other respects resembles the last. It is given as follows : 1 lb. sodium carbonate, 1/2 lb. caustic lime, 2 1/2 pints water. Boil together, let it stand to settle, then draw off the clear lye, and add to it 1 lb. tallow, 1/2 lb. rosin, previously melted together. Boil and stir occasionally for 1/2 hour, then introduce 3 oz. glue (previously softened), 3 oz. linseed oil, and continue the boiling and stirring for another 1/2 hour. In waterproofing, 1/2 oz. of this soap is mixed with 1 gal. hot water, and in this the goods are soaked for about 24 hours, according to thickness and character. The pieces are allowed to drain until partly dried, then soaked for 6 hours or more in a solution prepared as follows: 1 lb. aluminium sulphate, 1/2 lb. lead acetate, 8 gal. water. Shake together, allow to settle, and draw off the clear liquid. Wring out alter rinsing, and dry at a temperature of 80°F. (27° C).
(4) In Reimann's process, the cloth is passed slowly by machinery through a tank divided into 3 compartments, the first containing a warm solution of alum, the second a warm solution of lead acetate, and the third pure water, which is constantly renewed. The cloth on passing from the latter is brushed and beaten to remove the salt adhering to the surface, and finally hot-pressed and brushed. In this case, lead sulphate is deposited in the fibres.
(5) In Townsend's process, 2 solutions are used as follows: 20 lb. dextrine, 10 lb. white soap, 16 gal. water. The solution is boiled for some minutes, and if colour is required, 1 pint logwood liquor is added. The second solution consists of a saturated solution of alum in water, or 6 lb. zinc sulphate, 9 gal. water.
(6) Bullard's process is somewhat similar to Reimann's. In this, strong aqueous solutions of aluminium sulphate and lead acetate are used alternately.
(8) A bath heated to 194° F. (90° C.) is made of 13 1/4 lb. liquid Bordeaux turpentine, 3 1/4 lb. tallow, 1 lb. wax, and lb. storax; the articles are immersed for a few minutes, then passed between heated rollers to remove excess.
(9) For some time past the Belgian War Department has conducted a series of experiments at Valvorde, on the waterproofing of soldiers' uniforms by means of liquid alumina. With respect to the hygienic side of the question, the medical authorities have satisfied themselves that the articles of dress thus treated permit the perspiration to pass off freely, and chemical analysis has proved that the preparation used in no way injures the materials, or destroys their colour. More than 10,000 yd. of materials, re-dressed 2 or 3 times over, notwithstanding the rinsing and washing to which they have been subjected after having been soiled, and after constant wear, remained perfectly waterproof. The only drawback to the process appears to be that it is not very economical, and, to ensure the desired result, must be conducted on a large scale, which requires a considerable amount of plant. The following is the process employed : - Alumina acetate is obtained by making solutions of equal parts of alum and lead acetate in separate vessels, and then mixing them together. Lead sulphate will be thrown down, leaving alumina acetate in solution, which must be decanted.
The materials to be waterproofed are soaked in this solution, and then withdrawn without being wrung, and dried in the air.
(10) Bellefroid produces an impermeable coating, which consists firstly of a solution of stearine pitch, one of the by-products of candle-making, which pitch, in order to be used in the fabrication of the compound, is previously completely oxidised by exposure to the air. In order to complete this oxidisation, the pitch is spread out in very thin layers, and exposed to the outer atmosphere for a period of at least 2 years. This exposure is absolutely necessary, judging from experiments repeatedly made. The solution is afterwards effected in the following manner. A mixture consisting of 75 lb. stearine pitch, 150 lb. water, and 5 lb. caustic soda at about 35° to 36°, is put into a boiler or vessel of any suitable shape, having a second or double bottom so as to allow of the removal of impurities which will settle at the bottom of the vessel. The mixture is boiled for 12 hours over a strong fire, after which 52 pints water are added, and the boiling is continued for another 12 hours. The solution thus obtained is then poured out in an open vessel, and left exposed to the open air for 8 days, for the purpose of being clarified, and enabling the impurities to settle at the bottom.