1 kg of water saturated with hydrogen chloride at 15°c forms 1.75 kg of 43% solution, density 1.231.
By saturating a strongly cooled solution with the gas (HCl) three solid hydrates are formed : HCl,H2O (mp -15.35°c), HCl,2H2O (mp -17.7°c) and HCl,3H2O (mp -24.4°c).
(Rupert, J.A.C.S.,1909,31,851)
Umm, how interesting !!