The characteristics of a large-area liquid scintillation counter are investigated and the uniformity of response of the counter over its area is measured and compared with theory. Using a paraffin phosphor the uniformity is ±8% when the scintillation light is collected by total internal reflection and ±4% when the bottom face of the counter is covered with a diffusing surface. The response of the paraffin phosphor is found to be increased by a factor of 4 by the addition of 10% shellsol A, which makes the response comparable with that of plastic NE 102. The large area scintillation counter is used in an energy loss experiment with a horizontal cosmic ray spectrograph as a "source" of relativistic muons. The results are consistent with conventionally accepted theory to the highest momenta investigated. No evidence is found for a decrease in ionisation loss of high energy muons (momenta >10 GeV/c) as recently predicted by Tsytovich
