| Conventional beer filters are made of either densely packed fibres or a dusty material called kieselguhr, which consists of fossilised hard-walled algae called diatoms. |
| The correct amount of kieselguhr to be added can only be ascertained by experience, and varies with different samples of yeast. |
| Generally a small percentage of the kieselguhr is replaced by a mixture containing sodium and ammonium carbonates, talc and ochre. |
| A small amount of kieselguhr is generally added to improve the flowing properties. |
| In 1867, Nobel accidentally discovered that when nitroglycerin dripped on kieselguhr, a silicon-containing earth, it formed a paste that was stable and safer to use than liquid nitroglycerin alone. |
| By chance, he discovered that nitroglycerin was absorbed to dryness by kieselguhr, a porous siliceous earth, and the resulting mixture was much safer to use and easier to handle than nitroglycerin alone. |
