diff --git a/include/boost/units/physical_dimensions/drag_factor.hpp b/include/boost/units/physical_dimensions/drag_factor.hpp
new file mode 100644
index 00000000..493d6c16
--- /dev/null
+++ b/include/boost/units/physical_dimensions/drag_factor.hpp
@@ -0,0 +1,29 @@
+// Boost.Units - A C++ library for zero-overhead dimensional analysis and 
+// unit/quantity manipulation and conversion
+//
+// Copyright (C) 2003-2008 Matthias Christian Schabel
+// Copyright (C) 2008 Steven Watanabe
+// Copyright (C) 2015 Michael William Powell
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_UNITS_DRAG_FACTOR_DERIVED_DIMENSION_HPP
+#define BOOST_UNITS_DRAG_FACTOR_DERIVED_DIMENSION_HPP
+
+#include <boost/units/derived_dimension.hpp>
+#include <boost/units/physical_dimensions/length.hpp>
+
+namespace boost {
+
+namespace units {
+
+/// derived dimension for drag factor : L^-1
+typedef derived_dimension<length_base_dimension,-1>::type drag_factor_dimension;
+
+} // namespace units
+
+} // namespace boost
+
+#endif // BOOST_UNITS_DRAG_FACTOR_DERIVED_DIMENSION_HPP
diff --git a/include/boost/units/physical_dimensions/molar_mass.hpp b/include/boost/units/physical_dimensions/molar_mass.hpp
new file mode 100644
index 00000000..52d73c25
--- /dev/null
+++ b/include/boost/units/physical_dimensions/molar_mass.hpp
@@ -0,0 +1,31 @@
+// Boost.Units - A C++ library for zero-overhead dimensional analysis and 
+// unit/quantity manipulation and conversion
+//
+// Copyright (C) 2003-2008 Matthias Christian Schabel
+// Copyright (C) 2008 Steven Watanabe
+// Copyright (C) 2015 Michael William Powell
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_UNITS_MOLAR_MASS_DERIVED_DIMENSION_HPP
+#define BOOST_UNITS_MOLAR_MASS_DERIVED_DIMENSION_HPP
+
+#include <boost/units/derived_dimension.hpp>
+#include <boost/units/physical_dimensions/mass.hpp>
+#include <boost/units/physical_dimensions/amount.hpp>
+
+namespace boost {
+
+namespace units {
+
+/// derived dimension for molar mass : M Amount^-1
+typedef derived_dimension<mass_base_dimension,1,
+                          amount_base_dimension,-1>::type molar_mass_dimension;
+
+} // namespace units
+
+} // namespace boost
+
+#endif // BOOST_UNITS_MOLAR_MASS_DERIVED_DIMENSION_HPP
diff --git a/include/boost/units/physical_dimensions/specific_gas_constant.hpp b/include/boost/units/physical_dimensions/specific_gas_constant.hpp
new file mode 100644
index 00000000..b228f84d
--- /dev/null
+++ b/include/boost/units/physical_dimensions/specific_gas_constant.hpp
@@ -0,0 +1,46 @@
+// Boost.Units - A C++ library for zero-overhead dimensional analysis and 
+// unit/quantity manipulation and conversion
+//
+// Copyright (C) 2003-2008 Matthias Christian Schabel
+// Copyright (C) 2008 Steven Watanabe
+// Copyright (C) 2015 Michael William Powell
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_UNITS_SPECIFIC_GAS_CONSTANT_DERIVED_DIMENSION_HPP
+#define BOOST_UNITS_SPECIFIC_GAS_CONSTANT_DERIVED_DIMENSION_HPP
+
+#include <boost/units/derived_dimension.hpp>
+#include <boost/units/physical_dimensions/length.hpp>
+#include <boost/units/physical_dimensions/time.hpp>
+#include <boost/units/physical_dimensions/temperature.hpp>
+
+//#include <boost/units/physical_dimensions/energy.hpp>
+//#include <boost/units/physical_dimensions/mass.hpp>
+
+namespace boost {
+
+namespace units {
+
+///// derived dimension for specific gas constant : J M^-1 Theta^-1
+//typedef derived_dimension<energy_dimension,1,
+//                          mass_base_dimension,-1,
+//                          temperature_base_dimension,-1>::type specific_gas_constant_dimension;
+
+/// derived dimension for specific gas constant : J M^-1 Theta^-1
+/// which effectively reduces to                : L^-2 T^-2 Theta^-1
+typedef derived_dimension<length_base_dimension,2,
+                          temperature_base_dimension,-1,
+                          time_base_dimension,-2>::type specific_gas_constant_dimension;
+
+//typedef derived_dimension<energy_dimension, 1,
+//                          mass_base_dimension, -1,
+//                          temperature_base_dimension, -1>::type specific_gas_constant_dimension2;
+
+} // namespace units
+
+} // namespace boost
+
+#endif // BOOST_UNITS_SPECIFIC_GAS_CONSTANT_DERIVED_DIMENSION_HPP
diff --git a/include/boost/units/systems/si.hpp b/include/boost/units/systems/si.hpp
index 727982b4..18b427cb 100644
--- a/include/boost/units/systems/si.hpp
+++ b/include/boost/units/systems/si.hpp
@@ -36,6 +36,7 @@
 #include <boost/units/systems/si/current.hpp>
 #include <boost/units/systems/si/dimensionless.hpp>
 #include <boost/units/systems/si/dose_equivalent.hpp>
+#include <boost/units/systems/si/drag_factor.hpp>
 #include <boost/units/systems/si/dynamic_viscosity.hpp>
 #include <boost/units/systems/si/electric_charge.hpp>
 #include <boost/units/systems/si/electric_potential.hpp>
@@ -54,6 +55,7 @@
 #include <boost/units/systems/si/magnetic_flux_density.hpp>
 #include <boost/units/systems/si/mass.hpp>
 #include <boost/units/systems/si/mass_density.hpp>
+#include <boost/units/systems/si/molar_mass.hpp>
 #include <boost/units/systems/si/moment_of_inertia.hpp>
 #include <boost/units/systems/si/momentum.hpp>
 #include <boost/units/systems/si/permeability.hpp>
@@ -65,6 +67,7 @@
 #include <boost/units/systems/si/resistance.hpp>
 #include <boost/units/systems/si/resistivity.hpp>
 #include <boost/units/systems/si/solid_angle.hpp>
+#include <boost/units/systems/si/specific_gas_constant.hpp>
 #include <boost/units/systems/si/surface_density.hpp>
 #include <boost/units/systems/si/surface_tension.hpp>
 #include <boost/units/systems/si/temperature.hpp>
diff --git a/include/boost/units/systems/si/drag_factor.hpp b/include/boost/units/systems/si/drag_factor.hpp
new file mode 100644
index 00000000..86607abf
--- /dev/null
+++ b/include/boost/units/systems/si/drag_factor.hpp
@@ -0,0 +1,36 @@
+// Boost.Units - A C++ library for zero-overhead dimensional analysis and 
+// unit/quantity manipulation and conversion
+//
+// Copyright (C) 2003-2008 Matthias Christian Schabel
+// Copyright (C) 2008 Steven Watanabe
+// Copyright (C) 2015 Michael William Powell
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_UNITS_SI_DRAG_FACTOR_HPP
+#define BOOST_UNITS_SI_DRAG_FACTOR_HPP
+
+#include <boost/units/systems/si/base.hpp>
+#include <boost/units/physical_dimensions/drag_factor.hpp>
+
+namespace boost {
+
+namespace units { 
+
+namespace si {
+
+typedef unit<drag_factor_dimension,si::system>  drag_factor;
+
+BOOST_UNITS_STATIC_CONSTANT(dragfactor, drag_factor);
+
+// "K"
+
+} // namespace si
+
+} // namespace units
+
+} // namespace boost
+
+#endif // BOOST_UNITS_SI_DRAG_FACTOR_HPP
diff --git a/include/boost/units/systems/si/molar_mass.hpp b/include/boost/units/systems/si/molar_mass.hpp
new file mode 100644
index 00000000..d7fe459e
--- /dev/null
+++ b/include/boost/units/systems/si/molar_mass.hpp
@@ -0,0 +1,37 @@
+// Boost.Units - A C++ library for zero-overhead dimensional analysis and 
+// unit/quantity manipulation and conversion
+//
+// Copyright (C) 2003-2008 Matthias Christian Schabel
+// Copyright (C) 2008 Steven Watanabe
+// Copyright (C) 2015 Michael William Powell
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_UNITS_SI_MOLAR_MASS_HPP
+#define BOOST_UNITS_SI_MOLAR_MASS_HPP
+
+#include <boost/units/systems/si/base.hpp>
+#include <boost/units/physical_dimensions/molar_mass.hpp>
+
+namespace boost {
+
+namespace units { 
+
+namespace si {
+
+typedef unit<molar_mass_dimension,si::system>  molar_mass;
+
+BOOST_UNITS_STATIC_CONSTANT(kilogram_per_mole, molar_mass);
+BOOST_UNITS_STATIC_CONSTANT(kilograms_per_mole, molar_mass);
+BOOST_UNITS_STATIC_CONSTANT(kilogramme_per_mole, molar_mass);
+BOOST_UNITS_STATIC_CONSTANT(kilogrammes_per_mole, molar_mass);
+
+} // namespace si
+
+} // namespace units
+
+} // namespace boost
+
+#endif // BOOST_UNITS_SI_MASS_DENSITY_HPP
diff --git a/include/boost/units/systems/si/specific_gas_constant.hpp b/include/boost/units/systems/si/specific_gas_constant.hpp
new file mode 100644
index 00000000..583b688e
--- /dev/null
+++ b/include/boost/units/systems/si/specific_gas_constant.hpp
@@ -0,0 +1,37 @@
+// Boost.Units - A C++ library for zero-overhead dimensional analysis and 
+// unit/quantity manipulation and conversion
+//
+// Copyright (C) 2003-2008 Matthias Christian Schabel
+// Copyright (C) 2008 Steven Watanabe
+// Copyright (C) 2015 Michael William Powell
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_UNITS_SI_SPECIFIC_GAS_CONSTANT_HPP
+#define BOOST_UNITS_SI_SPECIFIC_GAS_CONSTANT_HPP
+
+#include <boost/units/systems/si/base.hpp>
+#include <boost/units/physical_dimensions/specific_gas_constant.hpp>
+
+namespace boost {
+
+namespace units { 
+
+namespace si {
+
+typedef unit<specific_gas_constant_dimension,si::system>  specific_gas_constant;
+
+BOOST_UNITS_STATIC_CONSTANT(joule_per_kilogram_kelvins, specific_gas_constant);
+BOOST_UNITS_STATIC_CONSTANT(joules_per_kilogram_kelvins, specific_gas_constant);
+BOOST_UNITS_STATIC_CONSTANT(joule_per_kilogramme_kelvins, specific_gas_constant);
+BOOST_UNITS_STATIC_CONSTANT(joules_per_kilogrammes_kelvins, specific_gas_constant);
+
+} // namespace si
+
+} // namespace units
+
+} // namespace boost
+
+#endif // BOOST_UNITS_SI_SPECIFIC_GAS_CONSTANT_HPP