544 



MICROBIOLOGY OF SPECIAL INDUSTRIES 



object being to have as large a surface as possible for the growth of the 

 bacterial film. Free circulation of air is insured by a s-cm. hole in 

 each head of the cask, one near the surface of the liquid and one near 

 the top of the cask, fhese holes should be covered with varnished 

 metal netting to prevent the entrance of flies. 



The top bung hole is then closed with a cork, through w-hich a funnel 

 passes, furnished at its lower end )vith a glass tube extending to within 

 a few inches of the bottom of the cask. By means of this funnel 

 new hquid can be added without disturbing the surface film. The 

 lower bung-hole is closed with a cork, through which passes an 

 L-shaped glass tube which serves as an indicator of level and which 

 also can be used to draw off the vinegar. 



Fig. 142. — Vinegar barrel. L, surface of liquid; 0, 0, openings for entrance of 

 air; t, tube for introducing new supplies of wine without distrubing surface films; 

 E, glass tube to show le,vel of liquid and for drawing off vinegar. (Original.) 



When this apparatus is working well, from one-fifth to one-quarter 

 of the contents may be taken off every three or four weeks. This 

 depends on the temperature, which should be between 10° and 18°. 

 The vinegar drawn off is immediately replaced with wine or cider which, 

 if added slowly, will, owing to its lower specific gravity, remain at the 

 surface in contact with the bacterial film. / 



Orleans Method. — This is practically the same as the method just 

 described with slight modifications to adapt it to large scale opera- 



