Successful experimental results can only be achieved by using clean apparatus.
Before the first use of glass-filters, they should be cleaned with diluted, hot hydrochloric acid, followed by several rinses with distilled water.
The following advice may be used for the massive and porous borosilicate glass 3.3:
Wash glassware as quickly as possible after use. During washing with water all parts of the article should be scrubbed with a soft brush. Avoid any abrasion of the glassware! After cleaning thoroughly rinse with distilled water. Drying of the soaked filters can be undertaken either in air or in a dry box at temperatures not exceeding 100° C. If after mechanical cleaning for example filter-pores should still remain clogged, the thorough chemical cleaning is required. A following are a few useful suggestions:
|Barium sulphate||Hot concentrated Sulphuric acid, Silver-chloride, Ammonia or Sodium hyposulfite|
|Copper/Iron Oxides||Hot Hydrochlorid acid plus potassium chlorate|
|Mercury residue||Hot Nitric acid|
|Mercury sulphide||Hot aqua regia|
|Albumen||Hot hydrochloric acid or hot ammonia|
|Grease, Oil, fatty materials||Carbon tetrachloride|
|Organic matters||Hot concentrated cleaning solution, or hot concentrated sulfuric acid plus a few drops of sodium or potassium nitrite|
|Glucose||Carefully heat to approx. 200° C with mixed acid (5% H2SO4 and 1% HNO3)|
Extensive rinsing with water must subsequently follow.
Hot, concentrated phosphoric acid and hot alkaline solutions attack the glass surface, they are unsuitable as cleaning agents. If they have to be filtered, an increase in poresize and reduced life of the sintered disc is unavoidable.