In the days when everything went by rail, some companies found it worth while building highly specialised vehicles for perishable traffics, which attracted premium rates, even if it meant those vehicles must have spent half their time running empty. One such traffic was dairy produce, and the MGWR, GSWR and GNR all built special “butter vans.” In the era before electrical refrigeration, these vans employed various cooling mechanisms like double roofs and multiple small vents in the body, presumably to make full use of the draft when in motion. I have not seen detailed plans of the internal layout of these designs, but I am guessing that they may have been “double-layered” with ice between two skins of planking, or may have used some sort of system where the evaporation of water from a porous surface (as in the older type of terra cotta milk or wine cooler), by taking latent heat of vaporisation from its surroundings, could effect considerable cooling. I seem to recall a school physics experiment which demonstrated this phenomenon rather well. It involved bubbling air through ether in a copper beaker, the beaker sitting in a small pool of water on a wooden block. By the time all the ether had evaporated, the whole apparatus was so cold that the beaker was frozen to the block by a lump of ice! Alphagraphix now make a 7mm and possibly a 4mm kit for this vehicle. I am grateful to the IRRS archives and Mr Brendan Pender for access to the GNR drawing and permission to reproduce it.