Is dissolution of H2S in water exothermic? While doing certain laboratory tests for qualitative identification of cations, I found that on passing $\ce{H2S}$ in the solution, the temperature of the solution increased considerably. When the temperature decreased due to addition of $\ce{NH4Cl}$, the solution again attained room temperature in passing $\ce{H2S}$.

This rouses the question: is the dissolution of $\ce{H2S}$ in water exothermic? Or does it react with other components of solution to make an exothermic reaction?

The Wikipedia article stated only this:


  Hydrogen sulphide is slightly soluble in water and acts as a weak acid (pKa = 6.9 in 0.01–0.1 mol/litre solutions at 18 °C), giving the hydrosulfide ion $\ce{HS^−}$. Hydrogen sulphide and its solutions are colourless.


The full experiment can be found here.
Koschel et al. (2013, p. 14486) report that 


  dissolution of gaseous hydrogen sulfide in aqueous phase is exothermic at conditions where $\ce{H_2S}$ is gaseous, i.e., at a temperature of 323 K and pressure 2 MPa, the saturation pressure $p_\text{sat}(\mathrm{H_2S})$ being 3.5 MPa. The dissolution process is endothermic at the medium and highest temperature where hydrogen sulfide is liquid and supercritical, respectively, the critical parameters of $\ce{H2S}$ being $T_c = 373.4$ and $p_c = 8.94$ MPa.