Results are reported for the formation of ammonium chloride by counter diffusion of ammonia and hydrogen chloride over the temperature range 25 - 40°C. Two modes of precipitation were observed, continuous and periodic precipitation (formation of Liesegang rings). The results establish that the presence of moisture is the important factor controlling the mechanism of precipitation, a minimum moisture content of approximately 100 ppm being required for formation of Liesegang rings. Under these conditions the concentration product was found to be very much greater than the thermodynamic minimum value confirming that nucleation of the solid product regulates the process.
On rapporte les resultats obtenus lors de la formation de chlorure d'ammonium par contre-diffusion de l'ammoniac et de l'acide chlorhydrique a une temperature variant entre 25 et 40°C. On a observe deux modes de precipitation, un continu et l'autre periodique (avec formation d'anneaux de Liesengang). Les resultats demontrent que la presence d'humidite est le facteur important qui regit le mecanisme de precipitation: une teneur minimale d'humidite d'environ 100 parties par million est necessaire pour qu'il y ait formation d'anneaux de Liesengang. On a trouve que, dans les dites conditions, le produit de concentration etait bien plus considerable que la valeur thermodynamique minimale, ce qui confirme le fait que la nucleation du produit solide regit le processus.
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