Acid-Alcohol is a simple mixture compounded from an acid and an alcohol, it's usual method of use is in bleaching or decolourising samples that contain a mixture of cells, some of which are resistant to acid bleaching and others that are not. These samples have usually been previously stained. The acid is generally hydrochloric and the alcohol can be ethanol or a mixture of ethanol, isopropanol and methanol, but other recipes are used in some cases.
The table below gives some typical recipes, but others may be found for special purposes and any other percentages can be calculated from the information the table contains.
|0.5%||O.5 ml||69.8 ml||29.7ml|
|1%||1 ml||69.3 ml||29.7ml|
|3%||3 ml||87 ml||5 ml||5 ml|
|3%||3 ml||92 ml||5 ml|
In order to illustrate the way that it may be used, the Ziehl-Neelsen method of staining acid-fast bacteria is described.
Acid-fast mycobacteria usually appear as slender, rod-shaped bacilli with dimensions in the range 1 to 10 µm long by 0.2 to 0.6 µm wide. They are generally straight, but can appear curved. The high lipid content (about 60%) of the cell wall makes the bacteria resistant to penetration by many dyes and chemicals.
A similar procedure, known as the Kinyoun method uses a wetting agent in the primary dye formulation, removing the need for heating.