What is the gold number?

She explained it as the protective power of a colloid... Didn't really understand it.
She explained it as the protective power of a colloid... Didn't really understand it.
Colloidal gold is a sol or colloidal suspension of nanoparticles of gold in a fluid, usually water. The colloid is usually either an intense red colour (for particles less than 100 nm) or blue/purple (for larger particles). Due to their optical, electronic, and molecular-recognition properties, gold nanoparticles are the subject of substantial research, with many potential or promised applications in a wide variety of areas, including electron microscopy, electronics, nanotechnology, and materials science.
The gold sol changes colour from red to blue/purple when the gold particles coagulate, i.e. gold particles combine to become larger. The coagulation of gold particles happens when 10% sodium chloride (NaCl) is added to the sol.
Gold Number is defined as the minimum amount of protective colloid in milligrams which prevents a color change from red to violet of 10ml gold sol by the addition of 1 ml of 10%NaCl solution.
There are different colloids with different gold numbers:
Gelatin: 0.005-.01
Haemoglobin: 0.03-0.07
Egg Albumin: 0.15-0.25
Potato Starch: 25
Gum arabic: 0.15-0.25
Caseinate: 0.01
Sodium Oleate: 1-5
Dextrin: 6-20
Based on the gold number, smaller quantities of gelatin are required to prevent the gold sol from coagulating and turning purple.