Triangulation of the quaternary Ag-Cd-Sn-S system in the Ag2SnS3-SnS-Sn2S3-CdS part below T = 600 K was performed using X-ray diffraction method. The spatial position of the determined four-phase regions regarding the figurative point of silver was used to write forming chemical reactions. The forming reactions were performed by applying electrochemical cells (ECCs): (-) C vertical bar Ag vertical bar Ag2GeS3 glass vertical bar Ag2CdSn3S8, SnS, Sn2S3, CdS vertical bar C (+) and (-) C vertical bar Ag vertical bar Ag2GeS3 glass vertical bar Ag2CdSnS4, SnS, Ag2CdSn3S8, CdS vertical bar C (+), where C is graphite and Ag2GeS3 glass is the fast purely Ag+ ions conducting electrolyte. The linear dependencies of the EMF of the ECCs on temperature in the range T = (462-500) K were used to calculate the standard thermodynamic values of the Ag2CdSn3S8 and Ag2CdSnS4 phases for the first time. (C) 2017 Elsevier Ltd.