y of the present invention is sealed with a silane sealant curve e its initial voltage drop is relatively low of the order of 50 millivolts and it decreases with service use thus it has been found that unlike the prior art tamping composition the shunt connection strength when employing the novel tamping composition y did not degrade after extended exposure to the current cycle test whether or not sealed when sealed with polyaryl sulfone it exhibited a high initial strength as well as final strength however the initial voltage drop was relatively high composition y when sealed with the silane sealant developed approximately the same high strength as when sealed with polyaryl sulfone while exhibiting low electrical resistance throughout specifically it was found that the connection strength for the brushes sealed with the silane curve e of fig2 remained substantially constant over the test period the millivolt drop measurement fig3 indicated a change from an initial value of 50 mv to a final value of 30 mv these are regarded as superior characteristics in that the final strength is high equal indeed to composition y with the polyaryl sulfone solvent and further the final millivolt drop is low being equal to or.