Suppose you are going to perform distillation under reduced pressure. You know that your substance boils at 89°C under pressure of 1 Torr. Unfortunately your pump cannot go that low. It can only achieve 5 Torrs of vacuum. What will be the boiling point of your compound under this pressure? The calculator can help. Generally three cases can be distinguished:
1. You know only one value of boiling point for your substance. In this case just fill the two upper fields with the values you know. You can now roughly evaluate its boiling point. Take water for example. Enter 760 (millimeters of mercury, or 1013 hPa -- units do not matter) as the pressure value and 100 as the boiling point. Now you can calculate its boiling point under any pressure. Type 15 in the second left field and 18 will appear in the second right field. This is the answer. Water boils at 18°C under 15 millimeters of mercury. Simple, isn`t it? You can do reverse calculation, too. You want to know what pressure is needed to make water boil at 50°C. Type 50 in the second right field and the result (89) will be displayed.
2. If you know the heat of evaporation of your substance you can enter it in the appropriate field. This should help to obtain more exact results. If you do not know the heat of evaporation, press the CHOOSE button and try to select your (or similar) compound from the list.
3. You know at least two boiling points under two different pressure values. You can sometimes find them in a journal or in tables. You are lucky then. Press the CALIBRATION button and fill in the form. The heat of evaporation of your substance will be calculated when you ACCEPT these data. This means you can obtain very accurate results now. Take crotonic acid for example: It boils at 185°C under 760 mmHg (atmospheric pressure) and at 80°C under 10 mmHg. Enter these data into calibration form and accept them. The heat of evaporation will be calculated and displayed (55.5 kJ/mol). You can evaluate the boiling point of crotonic acid quite accurately now.