Thanks to ixion #95 and greedykite #96.
Despite completing the crossword and fully 'getting' the theme/device I was completely stumped as to how the 22s 'worked.' Realised what the definition was but the wordplay beat me.
Won't go into all the weird & wonderful ways I tried to parse this - 'acid' = 'lsd' completely evaded me (haven't led a particularly sheltered life!) and L(itmus) P(aper) for 'new' currency also.
Thanks again.