FILTRATION OF BACTERIA 73 



B. 



Sulphanilic acid 0'5 gramme. 



Acetic acid (25 per cent, solution) . 1 50'0 c.c. 

 Mix solutions A and B together; the resulting mixture should be 

 colourless. The solution is best when freshly prepared, but if kept in 

 a close stoppered bottle retains its power for some time. 



Add 1 volume of the above solution to 5 volumes of the culture, 

 when if nitrites are present a deep red colour will appear in a few 

 seconds ; if no nitrites are present no changes take place. 



CXXXV. REICHEL'S BACTERIA FILTER. 



This apparatus consists of a glass flask and a porcelain filter which 



FIG. 22. 



Fin. 23. 



Reichel's Bacteria Filter. 



fits in the flask, and is used for separating bacterial products out of 

 culture media (see Fig. 22). 



CXXXVL METHOD OF USING THE FILTER. 



1. Place some cotton wadding in the glass tube at C, and also 

 at D. 



2. The porcelain cylinder B is placed in the glass flask, and both 

 sterilized in the hot-air sterilizer, a circular piece of asbestos being 

 placed between the under ring of the porcelain and the upper surface 

 of the neck of the glass flask. 



3. When the apparatus is removed from the hot-air oven, a special 

 perforated rubber cap is placed over the top of the filtering cylinder 



