19.4. References http://www.ck12.org
20.4 References
- Photogravure by H. Liffart, Berlin; scanned, image processed, and uploaded by Armin Kübelbeck. http://c
ommons.wikimedia.org/wiki/File:Claude_Louis_Berthollet_01.jpg. Public Domain - Alisha Vargas. http://www.flickr.com/photos/alishav/3953941345/. CC BY 2.0
- Christopher Auyeung. CK-12 Foundation. CC BY-NC 3.0
- Al Pavangkanan. http://www.flickr.com/photos/drtran/2186120627/. CC BY 2.0
- Christopher Auyeung. CK-12 Foundation. CC BY-NC 3.0
- Zachary Wilson. CK-12 Foundation. CC BY-NC 3.0