The Laboratory 71 



137). With these points in mind, a satisfactory 

 supply of water can be prepared. 



Salts must be accurately weighed. With the 

 exception of the sugar (see later) which can be 

 weighed on a coarse torsion balance in the media 

 room, all weighings should be carried out in the 

 laboratory room on high grade quantitative bal- 

 ances. 



The actual preparation of media will be dis- 

 cussed in a separate chapter and the glassware 

 required will be listed there. 



Glassware must be kept scrupulously clean 

 (Richards, 1936, 452). Carrel (see Parker, 1938, 

 26) boils his flasks in soap solution, rinses thor- 

 oughly with water and then with 95 per cent alco- 

 hol, and allows them to dry, after which they are 

 dry-sterilized. Vogelaar and Erlichmann (1939, 

 457) recommend washing in a sodium pyrophos- 

 phate solution. In this laboratory, it has been 

 customary to wash all glassware after use in a 

 sulfuric acid-potassium dichromate solution, made 

 up without added water. The cleaning solution 

 is kept in 3-gallon glazed crocks, such a crock 

 being placed in one corner of the vitreous or well- 

 paraffined sink. The flasks to be washed are first 

 emptied and, if they contain any solid matter, this 

 is rinsed out (Step 1 in the cleaning routine). 

 They are then placed in the acid and allowed to 



