▁until ▁his ▁ret irement ▁in ▁ 1 8 7 9 ▁at ▁age ▁ 6 6 . ▁ ▁He ▁died ▁in ▁ 1 8 8 5 , ▁and ▁was ▁buried ▁in ▁the ▁Bor ough ▁C emetery ▁in ▁B elf ast . ▁ ▁In ▁ 1 8 4 2 , ▁Andrew s ▁married ▁Jane ▁Hard ie ▁Walker ▁( 1 8 1 8 – 1 8 9 9 ). ▁They ▁had ▁six ▁children , ▁including ▁the ▁ge ologist ▁Mary ▁Andrew s . ▁ ▁Work ▁ ▁Andrew s ▁first ▁became ▁known ▁as ▁a ▁scientific ▁investig ator ▁with ▁his ▁work ▁on ▁the ▁heat ▁developed ▁in ▁chemical ▁actions , ▁for ▁which ▁the ▁Royal ▁Society ▁awarded ▁him ▁a ▁Royal ▁Medal ▁in ▁ 1 8 4 4 . ▁Another ▁important ▁investigation , ▁undert aken ▁in ▁collaboration ▁with ▁Peter ▁Gut hr ie ▁T ait , ▁was ▁devoted ▁to ▁o zone . ▁ ▁His ▁reputation ▁mainly ▁rest s ▁on ▁his ▁work ▁with ▁li que f action ▁of ▁g ases . ▁In ▁the ▁ 1 8 6 0 s ▁he ▁carried ▁out ▁a ▁very ▁complete ▁inqu iry ▁into ▁the ▁gas ▁laws — express ing ▁the ▁relations ▁of ▁pressure , ▁temperature , ▁and ▁volume ▁in ▁carbon ▁dio x ide . ▁In ▁particular , ▁he ▁established ▁the ▁concepts ▁of ▁critical ▁temperature ▁and ▁critical ▁pressure , ▁showing ▁that ▁a ▁subst ance ▁passes ▁from ▁v apor ▁to ▁liquid ▁state ▁without ▁any ▁bre ach ▁of ▁continu ity . ▁ ▁In ▁Andrew s ' ▁experiments ▁on ▁phase ▁trans itions , ▁he ▁showed ▁that ▁carbon ▁dio x ide ▁may ▁be ▁carried