In this notebook we'll calculate the characteristic Henry's constant at zero loading. Unlike fitting the entire isotherm with a Henry model, these methods will attempt to fit a straight line only on the initial part of the isotherm. First, make sure the data is imported.

```
In [1]:
```%run import.ipynb

```
```

```
In [2]:
```# Slope method
isotherm = next(i for i in isotherms_n2_77k if i.material=='MCM-41')
h1 = pygaps.initial_henry_slope(isotherm, max_adjrms=0.01, logx=True, verbose=True)
isotherm = next(i for i in isotherms_n2_77k if i.material=='UiO-66(Zr)')
h2 = pygaps.initial_henry_slope(isotherm, max_adjrms=0.01, logx=True, verbose=True)
print(h1,h2)

```
```

```
In [3]:
```# Virial method
isotherm = next(i for i in isotherms_n2_77k if i.material=='MCM-41')
h1 = pygaps.initial_henry_virial(isotherm, verbose=True)
isotherm = next(i for i in isotherms_n2_77k if i.material=='UiO-66(Zr)')
h2 = pygaps.initial_henry_virial(isotherm, verbose=True)
print(h1,h2)

```
```

More information about the functions and their use can be found in the manual.