August 1, 1919.] 



THE INDIA RUBBER WORLD 



631 



What the Rubber Chemists Are Doing. 



THE AUTHORS, Geoffrey Martin and James Wood, preface their 

 paper by noting that the tests given are all well known in the 

 trade, but as not much appears to have been published on the 

 subject the methods described may be of interest to chemists 

 who are called upon to examine cloth in regard to its water- 

 proof quality. 



Among the chief waterproofing processes may be mentioned 

 the following: 



1. With aluminum acetate. The fabric is immersed in a 

 solution of aluminum acetate, squeezed and dried, aluminum 

 oxide being deposited in the fiber. Fabrics thus waterproofed 

 are porous and permeable to air. They are not strictly water- 

 proof, and consequently are sometimes described as shower- 

 proof or rainproof. 



2. With gelatine, glue, isinglass, casein, etc., followed by treat- 

 ment with a solution of alum, tannin, etc. Here again the goods 

 are usually not absolutely impermeable to water. 



3. With parafine and other waxes. Articles treated in this 

 way are usually impermeable to water. 



4. With india rubber. 



5. With oil. A mixture of raw and boiled linseed oil mixed 

 with coloring matter, resin and other materials is spread in thin 

 layers on the fabric, which is dried between successive applica- 

 tions. Oiled silks, oil-skins, etc., impervious to water and air, 

 are thus prepared. 



6. With ammoniacal cupric oxide. The "Wellesden" fabrics 

 are waterproofed by this process. 



DETERMINATION OF WATERPROOF VAITTE. 



The Drop Test. This is the War Office test 

 and is especially valuable in that it furnishes 

 fairly> accurate numerical value of the de- 

 gree of waterproofing. It reproduces more or 

 less exactly the actual conditions to which a 

 cloth is subjected in practice, imitating the 

 natural fall of rain. 



The method of carrying out the test is 

 shown in the illustration. The sheet of cloth 

 to be tested is laid upon a sheet of white blot- 

 ting paper which in turn rests upon a sheet 

 of plate glass, supported by a frame at an 

 angle of 45 degrees. The cloth and blotting 

 paper are fixed in position by strips of lead 

 about an inch wide, bent at the end and laid 

 over the cloth. Beneath the plate glass is a 

 horizontal mirror. 



Water is dropped from the burette onto the 



cloth about five feet below. By means of the 



cock the flow of the water is kept at 20 drops 



per minute. This is continued until the water 



passes through the waterproofed cloth and 



stains the blotting paper below. By viewing 



Drop Test for the mirror from behind, the exact moment at 



Waterproof which the stain appears can be determined 



Fabrics. and the number of drops required to produce 



this result is noted. 



There is a considerable variation between the minimum and 



maximum number of drops required for penetration, but the 



average for a set of tests (20 trials per one half square foot) 



seems characteristic for any given piece of cloth. To pass the 



War Office test, an average of 60 drops is required. This is 



J "Journal of the Society of Chemical Industry," April 15, 1918, page 84T. 



considerably in excess of that usually needed in civilian garments. 

 The drop test is repeated on samples of the same cloth after 

 each of the following treatm.ents : 



1. The cloth should be rinsed three or four times in cold 

 water, dried, and tested again. A more severe test is to soak 

 the cloth in cold water for 24 hours, dry, and then again test. 

 A properly waterproofed cloth should not show much variation 

 when treated in this manner. 



2. The cloth should be covered with a damp cloth, ironed, and 

 again be subjected to the drop test. It is still better to blow 

 steam through it. The object of this test is to be sure that the 

 waterproofing is of such nature as to resist the treatment to 

 which the cloth will be subjecteed in the tailor's hands. 



FABRICS PROOFED WITH RtTBBER. 



In the case of fabrics proofed with india rubber, the War 

 Office specifies the composition of the proofing material. Thus, 

 the material for proofing coats with vulcanized india rubber mix- 

 ings must contain : mineral matter, not more than 41 per cent ; 

 sulphur not more than three per cent; india rubber not less than 

 56 per cent on the average, and no single coat may contain less 

 than 54 per cent. 



In the case of cyclists' waterproof capes, a different composi- 

 tion may be used for the proofing. The mineral matter must 

 not exceed 52 per cent, sulphur three per cent (the free sulphur 

 in this to be not more than one per cent). The rubber must not 

 be less than 45 per cent on the average, and no single garment 

 may contain less than 43 per cent. Civilian garments may con- 

 sist of different qualities from these, which represent a very high 

 class of waterproofing. 



ANALYSIS OF RUBBER PROOFING. 



Mineral Matter. A part of the sample is ignited and the weight 

 of ash determined. Due corrections are made for oxidation to 

 sulphates. When antimony sulphide and copper are present these 

 should be estimated in the usual way. The mineral matter used 

 for coloring the proofing of cylists' capes usually consists of rinc 

 oxide and litharge. Small additions of other ingredients such 

 as are generally recognized as having a beneficial influence are 

 officially recognized. The presence of calcium carbonate and 

 magnesium carbonate is often prohibited in War Office contracts. 



Sulphur is estimated in the usual way as barium sulphate, 

 oxidation being generally effected by nitric acid and potassium 

 chlorate. From a determination of the amount of antimony and 

 other metals present as sulphide in the preliminary operation, a 

 correction for the amount of sulphur combined with antimony 

 and other metals can be made. 



Free sulphur is regarded as the sulphur extracted by boiling 

 acetone. The substance is extracted by boiling acetone for about 

 one hour, the acetone evaporated, the residue oxidized, and the 

 amount of free sulphur determined as barium sulphate. 



Organic matter extracted by acetone is the difference between 

 total acetone extract and free sulphur. 



Alcoholic Potash Extract. The amount of organic matter 

 dissolved by boiling the acetone-extracted sample with alcoholic 

 potash is estimated as follows: 



The acetone-extracted rubber is dried and boiled for eight 

 hours with a solution of alcoholic potash (56 grains caustic pot- 

 ash in 500 cc. of alcohol). The solution is poured into a dish, 

 the rubber washed twice with alcohol and boiled two or three 

 times with water, the washings added, and the alcohol distilled 

 off and recovered. The residue is evaporated, washed into a 

 separating funnel, acidified with hydrochloric acid, and the fatty 

 acids extracted with successive portions of ether. The ether is 



