December 1, 1916.] 



THE INDIA RUBBER WORLD 



129 



have gone a couple of years longer and we can plot the curves, 

 it is possible that some relation can be shown. 



Mr. Wormeley also touched upon the effect of under-vulcaniza- 

 tion upon the results of the accelerated heat test : 



We have had some experience along this line in testing the 12 

 compounds already referred to as having been furnished by Dr. 

 Geer. Each of these compounds was represented by three cures, 

 one supposed to be the correct cure, one under-vulcanized and one 

 over-vulcanized. In plotting the effect of heat on tensile strength 

 and on elongation, three distinct curves were usually obtained for 

 each compound, the under-vulcanization being represented by the 

 top curve, the correct vulcanization by the middle curve, and the 

 over-vulcanization by the bottom curve. In the case of the lower 

 grade compounds, particularly those containing shoddy, there was 

 not much difference in the effect produced by the different degrees 

 of vulcanization. 



J. B. Tuttle followed, emphasizing the desirability of sup- 

 plementary chemical tests : 



All of those who have so far taken part in this discussion have 

 been using mechanical tests, such as tensile strength and elonga- 

 tion, as a measure of the rate of deterioration during aging. For 

 some four or five years, I have been making some tests on the 

 aging of rubber bands, by determining the amount of organic ace- 

 tone-soluble matter. These tests are still unfinished, but as far 

 as I have gone, the results are significant. Samples having an 

 initial acetone e.xtract of, say, 7 per cent or more, show a rapid 

 increase by the end of the first year. Those with 5 per cent show 

 very little change for a year or two, but increase rapidly after 

 that time. Samples with 4 per cent or less show practically no 

 increase in four years, and I cannot say just now what will hap- 

 pen to them during the next year. As far as their usefulness is 

 concerned, the 7 per cent bands are worthless at the end of a 

 year, and the 5 per cent bands in about three years. 



In considering these facts, it occurred to me that if we could 

 duplicate the conditions in a rapid test, then the chemical tests 

 would provide us with an excellent method for checking up the 

 results obtained by means of the mechanical tests. I have made 

 a few attempts along this line, but I have not yet been able to 

 duplicate the causes I have indicated here. It may be that, given 

 the correct temperature and length of time of heating, we would 

 be able to form a fairly accurate estimate of the probable Kfe of 

 the compound. 



I tried exposing samples to direct sunlight, and while the results 

 showed some promise, the time required was six weeks or more, 

 and, of course, is out of the question. 



So far as heating is concerned, the tests have not shown the 

 degree of difference in behavior of the 4, S and 7 per cent com- 

 pounds that I would like to see, but I believe that if this problem 

 could be satisfactorily worked out, it would be of great value in 

 cliecking the results obtained by means of the mechanical tests, 

 and thus be more certain that we are getting a good compound. 



An especially illuminating instance was cited to emphasize the 

 mistake of placing too much reliance on any one test. Said Mr. 

 Tuttle : 



We tested a shipment of rubber gloves intended for the Panama 

 Canal. Every glove was tested and found to be satisfactory, yet 

 within six months of the time after they had been shipped to 

 the Canal, and placed in storage there, they were found to be in a 

 defective condition. Some of these were returned for examina- 

 tion and further test. These gloves stood about 10,000 volts on 

 the break down test, but if you took one of them and simply bent 

 it once, it cracked all the way across. The tests of strength and 

 elongation are the important ones here. The gloves were all right 

 electrically as long as they were not in use. 



I have had similar experience with insulated wire. A few days 

 ago I was testing some wire which had been in service only a few 

 years. The electrical properties were satisfactory enough, but the 

 insulation had hardened so that if the wire was bent, the insulation 

 cracked. 



The point which I wish to bring out here is this : In making 

 these accelerated life tests, it is not sufficient to rely on one method 

 of testing only; if we are testing rubber insulation, we must make 

 the mechanical tests as well as the electrical tests, and I am not 

 at all certain that the time may not come when we shall add a 

 chemical aging test as well. 



Mr. Postmontier's remarks were directed to the possibilities 

 of an accelerated aging test and included valuable suggestions 

 for definite organization of the work: 



I am not in a position to make very many experiments of 

 this kind and I suppose that the rubber manufacturing labor- 



atories have neither the facilities nor the time; but it has struck 

 me that there is a possibility of a great amount of very important 

 and useful work that could be done by this Rubber Section. 

 There is always a difference between the rubber chemist and 

 the consumer as to the proper specification for rubber materials, 

 and it has occurred to more than one rubber chemist that many 

 times the specifications are drawn to a poorer grade of material 

 or a more expensive grade of material than the consumer might 

 use. On fillers and on rubber content which are called for in 

 different materials, we find a defect in many as to the best 

 materials. The consumer is always after the best material pos- 

 sible, but does not always know how to get it. The majority 

 of rubber manufacturers, being honest, are eager to give the 

 consumer the best material they can ; and it seems to me that 

 a coordination of rubber chemists in a section like this can do 

 very good work in determining what are the best materials for 

 the rubber compounds for different purposes. We experiment 

 with a very large amount of compounding material and a large 

 number of different kinds of rubber. It would be almost impos- 

 sible for any rubber laboratory, even the laboratory of a very 

 large manufacturing concern, to do the necessary work in exam- 

 ining the different features involved. There would always be 

 the element of difference as to the method of tests and liability 

 of result. 



There should be a committee appointed by the Rubber Sec- 

 tion, first of all, to standardize an accelerator test. It is a very 

 good test — probably no better test can be found — but at the same 

 time there are errors that may be introduced : A faster or a 

 slower current of air; questions as to the uniform temperature, 

 and so on ; questions on the heating principle might be brought 

 out. Standardized compounds might be suggested and different 

 laboratories that are willing to enter the work designated to 

 determine the effect of two or three more compounds. Gradually 

 the whole field of different compounds and rubbers could be 

 investigated and a great deal of important work accomplished 

 by this kind of coordination. 



E. A. Barrier believes that aging tests are not yet sufficiently 

 conclusive to be of great value to the consumer : 



I am quite sure that every consumer arranges to get all of 

 the cooperation he can from the manufacturer; but it seems to 

 me that this aging test is apparently not yet in a position where 

 it will be of very much value to the consumer. It is very evident 

 that there is no definite conclusion as to the normal life of rubber 

 in tlie aging test. What the consumer wants is a test that he 

 can actually see ; and if the sample shows up well in a few days 

 he wants to know that it will last two or three years. In the 

 accelerated aging test a sample may show good results in ten 

 days and the ten-day sample may last a shorter time in service 

 than the three-day sample. It is of value to the manufacturer, but 

 of no value to the consumer. Thirty per cent is a very wide 

 classification and also one that does not directly answer the 

 argurnent — that these accelerating tests show we have had very 

 little information as to the actual service condition. For instance, 

 this new specification which was discussed this morning con- 

 fines that to a type. Therefore, the consumer of insulated wire 

 under that specification could use this test, due to the fact that 

 a manufacturer is limited in his specific gravity, and for com- 

 mercial reasons, he has to bid as low as the next man, and if 

 he follows the specifications he will have the same compound, 

 or practically so. 



While not a chemist, Mr. Pierce expressed himself as particu- 

 larly interested in the subject of accelerated tests and hopeful of 

 an ultimate result. Said he : 



The consumer is not primarily interested in how strong the 

 wire is or anything else of that sort which you, as chemists, are 

 always working on, but the consumer is interested in knowing 

 whether that wire is going to be electrically insulated after one 

 or ten years. It occurs to me that if the work on this accelerated 

 test is to be continued and elaborated, it might be profitable to 

 learn whether the insulation shows good electrical properties 

 after this accelerated test, because that is the result you are 

 after. This is done now by chemical tests or mechanical tests, 

 and if it were possible to add to such accelerated tests, tests of 

 electrical properties, the insulation arrived at, etc., the results 

 would mean more to the consumer, and he would be able to grasp 

 it more readily. What the consumer is interested in, in the 

 case of wire, is the question of its electrical properties. 



Mr. Kimley then raised a point regarding the aging eflfect of 

 light : 



It occurs to me that perhaps the actual life of rubber is influ- 

 enced by light conditions. If it were standardized under the 



