To differentiate between Mercurius Solubilis (Merc Sol) and Arsenicum Album (Arsenicum) based on their modalities, consider the following:

1. Mercurius Solubilis (Merc Sol)
-Aggravated By: Symptoms worsen at night, in the warmth of the bed, while sweating, and lying on the right side.
-Ameliorated By: Symptoms improve with cold applications and in the open air.
-Other Modalities: Symptoms are aggravated by dampness, cold, and rainy weather.

2. Arsenicum Album (Arsenicum)
-Aggravated By: Symptoms worsen in cold air, from cold things, cold applications, and between midnight and 2 AM.
-Ameliorated By: Symptoms improve with warmth, warm drinks, and warm applications.
-Other Modalities: Symptoms are aggravated by wet weather and seashore exposure.

3. Key Differences
-Temperature Sensitivity: Merc Sol is aggravated by warmth and dampness, while Arsenicum is aggravated by cold and wet conditions.
-Time of Day: Merc Sol symptoms are worse at night, especially in the warmth of the bed, whereas Arsenicum symptoms are worse between midnight and 2 AM.
-Application: Merc Sol symptoms improve with cold applications, while Arsenicum symptoms improve with warmth and warm applications.