GLASSWARE 53 



ones, so that they are readily distinguishable by the eye. 

 The coloured wools may be purchased, or the ordinary 

 white wool may be dyed with the " Dolly " dyes. 



Glass vessels. The vessels (usually test-tubes, flasks, 

 and dishes) are thoroughly washed and rinsed in water, 

 then rinsed with 25 per cent, hydrochloric acid, and 

 afterwards washed well with tap-water and drained. A 

 final rinse with distilled water or alcohol is an advantage, 

 as no deposit then occurs on drying. The cleansed vessels 

 should be dried before sterilising, either in the air or by 

 placing in the hot-air steriliser for half an hour. When 

 dry, the vessels are plugged with a firm plug of the sterilised 

 cotton-wool, and are placed in the hot-air steriliser, the 

 temperature of which is then raised to about 150 C. 

 They should remain at this temperature for not less than 

 half an hour, after which the steriliser and its contents 

 are allowed to cool slowly. 



Petri dishes for plate cultures, graduated pipettes, etc., 

 are cleaned as described for tubes and flasks. They may 

 be sterilised and kept in sheet-iron or copper boxes of 

 appropriate size and shape. 



If tubes, flasks, pipettes, etc., are required in a hurry 

 they may be rapidly sterilised as follows : After washing 

 in water they are rmsed with 5 per cent, carbolic, then 

 with absolute alcohol, and finally with ether, and are then 

 well flamed over a Bunsen flame, holding in a suitable 

 forceps or holder. The ether evaporates and burns at 

 the mouth, and when dry, a pledget of cotton-wool is held 

 in the forceps and singed in the flame, and, while burning, 

 the tube or flask is plugged with it. 



When thick glass vessels, such as measures, etc./ have 

 to be sterilised, it is not safe to do this in the hot-air 

 steriliser unless the heating and cooling are carried out 

 very slowly, as they are very liable to crack. It is prefer- 

 able, after cleaning and plugging with sterile wool, to 



