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181 n. Testing of Caoutchouc Articles. The Laboratory has tested several of this kind of articles, for instance, caoutchouc hoses, caoutchouc packing rings and rub- ber soles. For hoses the caoutchouc has especially been chemically examined, but tests of resistance to internal pressure have also been made. As to caoutchouc packing rings and other packing rings the Laboratory has for one thing , tested them in clasping different sorts between flanges in an apparatus, to which saturated or over- heated steam could be led during a longer period, and then re- searching whether they were tight during the experiment and how their state was when taken out of the apparatus. In Report II of the Laboratory details are given as to a variation of this method. Such a method gives, of course, no definite particulars as to how the packings will hold out when used, but only some in- formation. Fig. 35 at p. 95 shows to the left 4 different new packing rings, and to the right they are seen after going through the same treatment in an apparatus as that recorded in Report II, and it is to be seen how extremely unlike different packing rings stand the same treatment. This picture has not been published before. For the testing of resistance to wear of rubber soles the La- boratory — as recorded in »Baumaterialienkunde« 1905, Nr. 11 —12 — employed a similar method as for the testing of linoleum. As only smaller pieces of rubber soles can be obtained, these can not without further ceremony be fastened on the plate-glass instead of the linoleum, not affording sufficient guiding for the wooden block, covered with sand-paper and wandering to and fro; the latter will therefore begin to swing when moving, and the me- thod has been modified so far that a piece of Carborundum-paper is laid round the plate-glass, while under the block 2 rectangular test-pieces are fastened at the ends, namely 1 taken out of each rubber sole. Not to spoil the wooden block, the test-pieces are not pasted directly under it, but on the underside of the block there is screwed a couple of aluminium plates and to these the test-pieces are pasted by means of a solution of caoutchouc. The aluminium plates project a little beyond the test-pieces so that outside these