TmE quality of adhesion of bituminous compounds, when hot and cold, to their containers is of the utmost importance to ensure the exclusion of moisture.
A qualitative test of immersing a silver steel rod into the hot material and withdrawing it when cold, leads to the formation of a cone of the compound when the adhesiveness is satisfactory.
A more exact measurement is obtained vHth an apparatus that consists, in essence, of a cylindrical steel mould, filled with the material under test, standing on a very carefully polished steal plate. The mould and plate are subjected to a slow steady pull apart; and after separation the area covered by the sample is examined as to whether the compound has adhered over an area not less than 90% of the whole. In practice there are very few border-line cases.
The temperature of the mould when it is being filled varies according to the class of material tested; and that of the test is 20 5 C.
Plastic Flow, considered as a property of distilled bitumen (regarded as a "fluid") and blown bitumen (regarded as being of the "solid" type, being more subject to fracture by shock), has had very little work done upon it.
Six questions have been formulated concerning this property, the answers to which would give a deep insight into the nature of these substances.
A full report on the selection of bitumens for use in the electrical industry is presented in another paper. For the convenience of the Congress the subjects of adhesiveness and plastic flow are not included therein, but are dealt with below. That report may be referred to for particulars of the interest of the British Electrical and Allied Industries Research Association in this subject and of the classes of compound recognised by the Association.
Adhesivenms :-For use in electrical gear and apparatus, adhesion to the sides of the container is of the utmost importance. The fact that the compound is poured hot implies contraction when introduced into the finished gear. Further, a compound which does not stick to the container leaves open the possibility of moisture entering, particularly in outdoor apparatus. Several methods of applying a test for adhesiveness have been advanced from time to time, none of which is really quite satisfactory. A very simple test is to stick a rod of silver steel into the hot compound, and to withdraw it when cold. In most cases a cone of compound is drawn out when the rod is pulled out, and this is a fairly good qualitative test. It does not, however, lend itself to adequate description. Partly for this reason the following test has been used A steel mould (A) in the form of a cylinder of the dimensions shown in Fig. 1 is placed on a steel plate (B). The mould contains two dowels fitted in one end which register easily in holes (C) and (D) in the plate. A hole is drilled through the wall of the moul