RAIN-PROOF FABRICS. The production of rain-proof textures may be divided into two classes—those that are made into garments of various kinds; and those that are made for the protection of goods. In some instances, the cloth is either covered with a layer of some suitable solution, rubber or the like, or else the interstices between the warp and weft (filling) threads are filled by means of some substance that will prevent, for a length ened period, the penetration of moisture.
Light raincoats and oilskins are often termed "macintoshes" be cause some of the earlier garments were patented and made by one named Macintosh ; these contained substances such as rubber and asbestos, but in the modern water-proofs different materials are used. Production of rain-proof garments in which rubber is used is closely identified with rubber manufacture (q.v.).
Variously coloured light-weight rain-proof oilskin in a consider able quantity is manufactured for several purposes, the founda tion of many of these cloths being either Jap silk or good quality cotton made from Egyptian yarns. The cloths may be dyed be fore the proofing or the dyestuff may be mixed with the proofing solutions, which are composed largely of high-grade oil (boiled linseed oil or the like) and suitable substances such as sulphur, wax, resin and mineral pigments, though in some cases rubber solutions are used. A few of the heavier types of cloth, such as those that are ultimately made into garments for fishermen, farm labourers and others likely to be out in long periods of inclement weather, are still made by hand, but, in general, rain-proof gar ments are both proofed and made up by machinery.
The procedure in the mechanical manipulation is to proof the material and then to heat it to the correct degree of temperature in suitable stoves. The principal methods of proofing are I. The application to the fabric of a coating of, say, india rubber, varnish, boiled linseed oil, paraffin wax and similar sub stances.
2. The impregnation of the fabric, or rather its cells and pores, with substances in solution such as paraffin wax, ceresine and metallic soaps in benzene or naphtha, pitch and tar.
3. The precipitation of insoluble compounds in the fibres or yarns of which the cloth is made, such as metallic compounds (oxides and hydrates) or metallic soaps.
4. The parchmentizing of the fabric by a solution of ammo nium cuprate.
As indicated, linseed oil is usually applied as a mixture of raw oil, boiled oil and driers, together with the desired pigment. The mixture is contained in a tank and the cloth is passed full width through this mixture, the excess solution squeezed out and the fabric hung up for 1 o to 14 days for the oil to oxidize. Two or three coats of the solution may be applied. Some mixtures con tain about 88% boiled oil, 8% terebene drier and 4% vegetable black. Pitch is heated, run hot on to the fabric and spread evenly either by hand or mechanical brushes. The pitch is sometimes applied to both sides of the cloth. Metallic soaps for water proofing are made by precipitating good quality soap with metallic salts, and the solutions prepared from them are used for certain classes of waterproofing, e.g., alum for white soap, copper for green soap, and ferrous sulphate for red soap. These metallic soaps are dissolved in naphtha and the mixture stirred and heated by suitable appliances. Paraffin wax is sometimes added to obtain a heavy deposit on the fabric and filling agents are also largely used. The cloth is passed slowly through the solution so that thorough impregnation may result. The excess liquid is squeezed out and the cloth then hung up so that the naphtha may evapo rate, or it is passed through a long duct through which hot air circulates, and, finally, the cloth is dried.
Another method of waterproofing is to precipitate insoluble compounds in the fibres of the yarns contained in the cloth. Alu minium acetate, diluted to the correct degree, is used for the proofing. In other cases, a solution of copper oxide in ammonia (Schweitzer's reagent) is used in sufficient quantity to dissolve about 21% of its weight of cotton. The cloth is passed through this solution, after which it is dried by hot air, and thus the ammonia is volatilized and the dissolved cellulose and copper oxide are precipitated on to the cloth.
See The Waterproofing of Fabrics by Dr. S. Mierzinski, and The Finishing of Jute and Linen Fabrics by T. Woodhouse. (T. W.) (Pithecolobium saman), a tropical South American tree, so called from the fact that the ejection of juice by cicadas (q.v.) upon it causes it to appear to be always raining under its branches. Andira inermis, which belongs to the same family (Leguminosae), is also called rain-tree for the same reason.