From 6891c324cf1b73742b05c60f8112edecf9d22830 Mon Sep 17 00:00:00 2001
From: Ryan <rkingsbury@users.noreply.github.com>
Date: Tue, 15 Aug 2023 15:46:27 -0400
Subject: [PATCH] Solution: adjust vol for T and P changes + add tests

---
 CHANGELOG.md           |  1 +
 src/pyEQL/solution.py  | 14 ++++++++++++++
 tests/test_solution.py | 12 +++++++++++-
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5ac7d2c2..c19aca90 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- `Solution`: add tests to confirm that solution density changes with temperature and pressure
 - `Solution`: add tests for `charge_balance`, `alkalinity`, `hardness`
 - `Solution`: add support for passing solutes as a `dict`
 - Implement extensible system for connecting `Solution` to various activity and speciation
diff --git a/src/pyEQL/solution.py b/src/pyEQL/solution.py
index 4d06488a..bc8f598f 100644
--- a/src/pyEQL/solution.py
+++ b/src/pyEQL/solution.py
@@ -298,6 +298,13 @@ def temperature(self, temperature: str):
             temperature: pint-compatible string, e.g. '25 degC'
         """
         self._temperature = unit.Quantity(temperature)
+
+        # update the water substance
+        self.water_substance = IAPWS95(
+            T=self.temperature.magnitude,
+            P=self.pressure.to("MPa").magnitude,
+        )
+
         # recalculate the volume
         self.volume_update_required = True
 
@@ -315,6 +322,13 @@ def pressure(self, pressure: str):
             pressure: pint-compatible string, e.g. '1.2 atmC'
         """
         self._pressure = unit.Quantity(pressure)
+
+        # update the water substance
+        self.water_substance = IAPWS95(
+            T=self.temperature.magnitude,
+            P=self.pressure.to("MPa").magnitude,
+        )
+
         # recalculate the volume
         self.volume_update_required = True
 
diff --git a/tests/test_solution.py b/tests/test_solution.py
index f0bd1434..93421cfe 100644
--- a/tests/test_solution.py
+++ b/tests/test_solution.py
@@ -8,7 +8,7 @@
 
 import numpy as np
 import pytest
-from pyEQL import Solution
+from pyEQL import Solution, unit
 
 
 @pytest.fixture()
@@ -116,6 +116,16 @@ def test_alkalinity_hardness_chargebalance(s3, s5, s6):
     assert np.isclose(s6.hardness.magnitude, 600, rtol=0.005)
     assert np.isclose(s6.charge_balance, -0.12)
 
+def test_pressure_temperature(s5):
+    orig_V = s5.volume
+    s5.temperature = '50 degC'
+    assert s5.temperature == unit.Quantity('50 degC')
+    assert s5.volume > orig_V
+    intermediate_V = s5.volume
+    s5.pressure = '2 atm'
+    assert s5.pressure == unit.Quantity('2 atm')
+    assert s5.volume < intermediate_V
+
 def test_serialization(s1, s2):
     assert isinstance(s1.as_dict(), dict)
     s1_new = Solution.from_dict(s1.as_dict())